Custom Detection Rules as Code in Sentinel Repositories: What Your Pipeline Owns Now
While going through the June Sentinel updates I almost scrolled past this one, and I think that would have been a mistake: custom detection rules can now be managed as code in Sentinel Repositories, the same way analytics rules, playbooks, parsers and workbooks already are. You connect a GitHub or Azure DevOps repo, enable the Custom Detection Rules content type, and rules are synced on every commit. There is also a standalone path via the Bicep CLI for teams running their own pipelines. The feature is in preview per the Learn documentation, and in my view it matters more than the low-key rollout suggests. Microsoft has been positioning custom detections as the unified experience for building rules over both Defender XDR and Sentinel data since late 2025. If custom detections are becoming the primary detection type, then this preview is the moment your primary detection type becomes pipeline-managed. I spent some time in the documentation to understand what that actually means, and there is one implication I have not seen anyone talk about yet. How it works Custom detection rules use a different mechanism than every other content type in Repositories. Analytics rules deploy as Microsoft.OperationalInsights/workspaces/providers/alertRules resources, with the Microsoft.SecurityInsights provider sitting in the resource name. Custom detection rules instead use a dedicated Bicep extension. You declare it in a `bicepconfig.json` at the repo root: { "extensions": { "MicrosoftSecurity": "br:mcr.microsoft.com/bicep/extensions/microsoftsecurity:v1.0.1" } } The rule itself is a `Microsoft.Security/detectionRules` resource. This is the structure from the Microsoft documentation: extension MicrosoftSecurity resource detectionRule 'Microsoft.Security/detectionRules@2026-06-01-preview' = { id: 'custom-rule-id' displayName: 'Custom Rule Display Name' status: 'enabled' queryCondition: { queryText: 'DeviceProcessEvents | take 10 | project DeviceId, Timestamp, FileName' } schedule: { frequency: 'PT1H' } detectionAction: { alertTemplate: { title: '<ruleTitle>' description: 'Custom detection rule' severity: 'medium' tactics: [ { tactic: 'Execution' techniques: [ { technique: 'T1059' } ] } ] entityMappings: { hosts: [ { id: 'h' deviceIdColumn: 'DeviceId' } ] } } } } Rules are uniquely identified by the `id` property, which you provide in the template. Deployment is either the automatic Repositories sync or a plain `az deployment group create` against a resource group. That last part is what I like most about the design: any CI/CD system that can run Azure CLI can ship these rules. Prerequisites beyond the standard Repositories setup: a Microsoft 365 E5 license or equivalent that includes Defender XDR, and a Sentinel workspace onboarded to the Defender portal. Two preview limitations are documented: custom frequency for Sentinel-only data is not supported yet, and neither are custom details. The part that made me stop reading and think Repositories are designed as the single source of truth. The documentation is explicit that content in your repo overwrites changes made through the portal. That is the whole point of the feature, and for analytics rules it has been mostly harmless. For custom detections I see a wrinkle. When Microsoft renames tables or columns in the advanced hunting schema, those naming changes are applied automatically to queries saved in Microsoft Defender, including the queries inside custom detection rules. The docs are equally explicit that this automatic migration does not cover queries run via API or saved anywhere outside Defender. A Git repo is outside Defender. Play that forward with a current example. The `AIAgentsInfo` table stopped being accessible on July 1, 2026, replaced by the unified `AgentsInfo` table with a changed column set. A portal-managed custom detection referencing the old table got migrated automatically. The same rule managed as code did not, because the authoritative copy of the query now lives in your repo, and nothing in the sync path rewrites your Bicep files. Your repo is now the thing standing between Microsoft's server-side fix and your production detection. Either the sync starts failing, or the stale query gets reasserted over the migrated rule. The documentation does not say which of the two happens, and honestly, neither is good. No alert fires for either. And if smart deployments, which skip files that have not changed since the last deployment, apply to this content type the same way they do to the rest of Repositories, it gets slightly worse in a way I find almost funny: a stale rule would sit untouched until someone happens to edit it. What I would put in front of the merge To be clear, none of this is an argument against the feature. I want detections in Git, and I suspect most people reading this do too. It is an argument that moving custom detections into a repo moves the schema lifecycle responsibility into your review process, because the portal safety net explicitly does not reach into source control. Concretely, a PR touching detection content should be checked for references to deprecated or transitioning advanced hunting tables, for the result columns the custom detection docs recommend (`Timestamp` or `TimeGenerated`, plus `DeviceId` or `DeviceName` for Defender for Endpoint tables, plus `Timestamp` and `ReportId` from the same event for the other Defender tables), and for complete entity mappings, since entities drive how alerts group into incidents. One more detail from the custom detection docs that I suspect will trip up people coming from analytics rules, because it goes against years of muscle memory: avoid filtering on `Timestamp` or `TimeGenerated` in the query itself. The service prefilters data based on the detection lookback using ingestion time. The scheduled-analytics-rule reflex of always pinning a time window works against you here. Whether you enforce these checks with a homegrown script or a linting step in the pipeline matters less than doing it before merge rather than discovering it in the alert queue. The deployment mechanics are now solved. The content governance is yours. Full transparency: I have worked through the documentation and the sample content, but I have not yet run a retired-table scenario through the sync myself. So if you are testing the preview, I would genuinely like to hear how it behaves in your environment when a repo-managed rule references a table like `AIAgentsInfo`. That failure mode is the one I want to understand before this reaches GA. Beyond that specific case, I am curious where you all stand: are you moving custom detections into Git now, or waiting for GA? And if you already run detections as code for analytics rules, what checks have earned a permanent place in your PR pipeline? My used references: Manage content as code with Microsoft Sentinel repositories: https://learn.microsoft.com/en-us/azure/sentinel/ci-cd-custom-content Advanced hunting schema naming changes: https://learn.microsoft.com/en-us/defender-xdr/advanced-hunting-schema-changes Create custom detection rules in Microsoft Defender XDR: https://learn.microsoft.com/en-us/defender-xdr/custom-detection-rules Custom detections as the unified detection experience: https://techcommunity.microsoft.com/t5/microsoft-defender-threat-protection/custom-detections-are-now-the-unified-experience-for-creating/ba-p/4463875Registration Open: Community-Led Purview Lightning Talks
Get ready for an electrifying event! The Microsoft Security Community proudly presents Purview Lightning Talks; an action-packed series featuring your fellow Microsoft users, partners and passionate Microsoft Security community members of all sorts. Each 3-12 minute talk cuts straight to the chase, delivering expert insights, real-world use cases, and even a few game-changing tips and tricks. Don’t miss this opportunity to learn, connect, and be inspired! Secure your spot now for the big day: April 30th at 8am Redmond Time. See agenda details below and follow this blog post (sign in and click the "follow" heart in the upper right) to receive notifications. ❗UPDATE❗This event is expected to last around 2 hours and 15 minutes, due to the incredible number of community sessions that were submitted! 💖 Please see the timing table below broken out into sections of four talks each, and plan to arrive 10 minutes before the section that interests you, OR stay for the whole time! Speakers will be available in the chat to answer your questions; please ask your questions during their session. Spillover Q&A forum links will also be shared. The full session recording will be indexed and posted to Microsoft Security Community YouTube within 24 hours after the event. Bookmark this page or follow this blog post for updates! Agenda Legend ↩️ Data Lifecycle Management 🔐 Information Protection 🚫 Data Loss Prevention (DLP) 🦾 Data Security Posture Management (DSPM) for AI 🤖 Purview for AI 👁️ Insider Risk Management (IRM) 🔍 eDiscovery 📊 Governance 🗒️ Compliance Manager 🛡️ Data Security All times are listed in US Pacific/Redmond Time. Session lengths are rounded to the nearest minute. AGENDA Section 1 - approximately 8:00 am - 8:43 am ↩️ The Day Offboarding Exposed Infinite Retention — Nikki Chapple Length: 10 minutes | Topic: Data Lifecycle Management A routine Purview request led to an unexpected discovery: more than 9,000 orphaned OneDrives and thousands of inactive mailboxes still storing content long after employees had left. This talk explains how a retain-only policy created hidden retention debt and how Adaptive Scopes can help organisations separate active users from leavers to avoid similar pitfalls. 🔐 The Purview Label Engine: Automated Classification, Translation, and co-Documentation for Enterprise Tenants — Michael Kirst-Neshva Length: 12 minutes | Topic: Information Protection Global enterprises face the challenge of implementing uniform data protection standards across borders and languages. In this talk, I’ll present a framework that makes Microsoft Purview labels truly scalable. Discover how to roll out parent and child label logics automatically, manage priorities with a single click, and generate instant compliance documentation for every business unit. 🗒️ What's In My Compliance Manager Toolbox: A Cloud Security Architect's Perspective — Jerrad Dahlager Length: 8 minutes | Topic: Compliance Manager A practical walkthrough of how I use Compliance Manager across real client engagements to map controls, track improvement actions, and simplify multi-framework compliance. No theory, just what works in the field. 🛡️ Stop, Think, Protect: Data Security in Real Life with Purview — Oliver Sahlmann Length: 8 minutes | Topic: Data Security With simple labels and matching DLP policies, Purview offers a practical and accessible way to approach data security. This lightning talk uses a real-life traffic light concept to show how a low barrier to adoption can still drive meaningful protection and awareness. Section 2 - approximately 8:44 am - 9:15 am 🔐 Using Purview to prevent oversharing with AI services — Viktor Hedberg Length: 10 minutes | Topic: Information Protection In this day and age, AI is the big thing. However, Copilot has access to everything you can access, including potentially sensitive data. In this session we will look at how to prevent Copilot to access highly sensitive data, using Information Protection. 🦾 How I Helped My Customers Understand their AI Usage (and protect their sensitive data) — Bram de Jager Length: 5 minutes | Topic: Data Security Posture Management (DSPM) for AI As AI tools explode across the web, many organizations still have no idea what’s actually happening in the browser—where employees type prompts, paste sensitive data, or visit public AI sites outside corporate governance. In this lightning talk, I’ll share how I helped customers shine a light on this issue. We’ll explore how Purview Data Security Posture Management (DSPM) can reveal which AI tools employees use, what types of data they input, and where sensitive information may leak through prompts. I’ll walk through real customer scenario where we detected risky AI usage patterns—such as employees pasting confidential documents into public chatbots. 🔐 Four Labels Max for Daily Use: Which Ones & Why? — Romain Dalle Length: 8 minutes | Topic: Information Protection Sensitivity labels are one of the most critical parts of a Purview Risk and compliance deployment, if not the most critical, because it directly impacts how end-users and business units should allow or restrict themselves to share their business data, internally and externally, on a daily basis. Labels have not other options than being precise, meaningful, and balanced in terms of embedded data security. Setting the right taxonomy is core to success, and is everything but a one-time project. 🚫 Data-driven Endpoint DLP Solution with Advanced Hunting — Tatu Seppälä Length: 8 minutes | Topic: Data Loss Prevention (DLP) This lightning talk shows you how to use KQL queries in advanced hunting to easily build initial sensitive service domain groups for authorized and unauthorized domains based on your organization's usage patterns. The same approach can be used for numerous other similar solution refinement and design purposes. Section 3 - approximately 9:16 am - 9:46 am 🔐 The Purview Hack No One Talks About: Container Sensitivity Labels That Fix Oversharing Fast — Nikki Chapple Length: 10 minutes | Topic: Information Protection Most organizations tackle oversharing with manual fixes, but the fastest solution is often overlooked. In this lightning talk, I show how container sensitivity labels automatically apply the right sharing and collaboration controls, ensuring every new Group, Team or SharePoint site starts secure by default. 🔍 Does M365 Support eDiscovery? — Julian Kusenberg Length: 11 minutes | Topic: eDiscovery A myth-busting session that separates perception from reality when it comes to Microsoft 365 eDiscovery capabilities. 📊 Improving Discovery, Trust, and Reuse of Analytics with Purview Data Products — Craig Wyndowe Length: 5 minutes | Topic: Governance This talk shows how bringing Power BI and Fabric assets into Microsoft Purview Governance Domains and Data Products creates a single, trusted view of enterprise analytics. By connecting reports, semantic models, and underlying data with shared metadata, ownership, and business context, organizations can make existing assets easy to discover and safe to reuse. 🔐 Why You Should Create Your Own Sensitive Information Types (SITs) — Niels Jakobsen Length: 5 minutes | Topic: Information Protection An in depth analysis of why Microsoft SITs are not one-size-fits-all, and how to create your own using what Microsoft has already built for you. Section 4 - approximately 9:47 am-10:30 am 👁️ From Zero to First Signal: Insider Risk Management Prerequisites That Actually Matter — Sathish Veerapandian Length: 8 minutes | Topic: Insider Risk Management (IRM) A focused live demo showing the real world prerequisites required for Microsoft Purview Insider Risk Management to work effectively. This session highlights the critical Entra ID, Intune, Microsoft Defender for Endpoint, and Purview DLP configurations that must be in place before creating IRM policies. 🤖 Securing data in the age of AI — Júlio César Gonçalves Vasconcelos Length: 11 minutes | Topic: Purview for AI AI will transform business as we know it; but without proper governance, it can introduce serious risks. We’ll show you how Microsoft Purview enables organizations to accelerate AI adoption while maintaining security, compliance, and transparency. 🔍 Beyond eDiscovery - Purview DSI for Security Investigation — Susantha Silva Length: 11 minutes | Topic: eDiscovery Most people hear “Microsoft Purview” and immediately think compliance, eDiscovery, or legal holds. But this session highlights Data Security Investigations, showing how DSI lets you take a DLP alert or insider risk signal and turn it into a structured investigation. 🚫 Elevating Purview DLP with a real world use case — Victor Wingsing Length: 14 minutes | Topic: Data Loss Prevention (DLP) Learn how I hardened Microsoft Purview DLP beyond out of the box defaults—closing real world data loss gaps, tuning policies to actual user behavior, and turning noisy alerts into protection that really blocks exfiltration. - Quick Closing/ Resource SharingStop identity attacks in real time with Microsoft Entra ID Protection
Modern identity security means stopping attacks before they escalate and extending protection beyond human users to apps and agentic identities across your identity fabric. Learn how Microsoft Entra ID Protection delivers premium, real-time identity protection with adaptive risk remediation, comprehensive detections, and expanded coverage for human and non-human identities. Powered by trillions of Microsoft Security signals and natively integrated with Microsoft Defender and Security Copilot workflows, Entra ID Protection enables faster and more accurate Conditional Access decisions that stop threats like lateral movement and privilege escalation before they spread. We'll show you how identity and security operations teams scale risk remediation with Entra ID, and how these capabilities extend across your broader identity security portfolio to strengthen protection in both cloud and hybrid environments. To learn more, read the Microsoft Entra ID Protection report. How do I participate? Registration is not required. Add this event to your calendar, then sign in to the Tech Community and select Attend to receive reminders. Post your questions in advance, or any time during the live broadcast.Sentinel to Defender Portal Migration - my 5 Gotchas to help you
The migration to the unified Defender portal is one of those transitions where the documentation covers "what's new" but glosses over what breaks on cutover day. Here are the gotchas that consistently catch teams off-guard, along with practical fixes. Gotcha 1: Automatic Connector Enablement When a Sentinel workspace connects to the Defender portal, Microsoft auto-enables certain connectors - often without clear notification. The most common surprises: Connector Auto-Enables? Impact Defender for Endpoint Yes EDR telemetry starts flowing, new alerts created Defender for Cloud Yes Additional incidents, potential ingestion cost increase Defender for Cloud Apps Conditional Depends on existing tenant config Azure AD Identity Protection No Stays in Sentinel workspace only Immediate action: Within 2 hours of connecting, navigate to Security.microsoft.com > Connectors & integrations > Data connectors and audit what auto-enabled. Compare against your pre-migration connector list and disable anything unplanned. Why this matters: Auto-enabled connectors can duplicate data sources - ingesting the same telemetry through both Sentinel and Defender connectors inflates Log Analytics costs by 20-40%. Gotcha 2: Incident Duplication The most disruptive surprise. The same incident appears twice: once from a Sentinel analytics rule, once from the Defender portal's auto-created incident creation rule. SOC teams get paged twice, deduplication breaks, and MTTR metrics go sideways. Diagnosis: SecurityIncident | where TimeGenerated > ago(7d) | summarize IncidentCount = count() by Title | where IncidentCount > 1 | order by IncidentCount desc If you see unexpected duplicates, the cause is almost certainly the auto-enabled Microsoft incident creation rule conflicting with your existing analytics rules. Fix: Disable the auto-created incident creation rule in Sentinel Automation rules, and rely on your existing analytics rule > incident mapping instead. This ensures incidents are created only through Sentinel's pipeline. Gotcha 3: Analytics Rule Title Dependencies The Defender portal matches incidents to analytics rules by title, not by rule ID. This creates subtle problems: Renaming a rule breaks the incident linkage Copying a rule with a similar title causes cross-linkage Two workspaces with identically named rules generate separate incidents for the same alert Prevention checklist: Audit all analytics rule titles for uniqueness before migration Document the title-to-GUID mapping as a reference Avoid renaming rules en masse during migration Use a naming convention like <Severity>_<Tactic>_<Technique> to prevent collisions Gotcha 4: RBAC Gaps Sentinel workspace RBAC roles don't directly translate to Defender portal permissions: Sentinel Role Defender Portal Equivalent Gap Microsoft Sentinel Responder Security Operator Minor - name change Microsoft Sentinel Contributor Security Operator + Security settings (manage) Significant - split across roles Sentinel Automation Contributor Automation Contributor (new) New role required Migration approach: Create new unified RBAC roles in the Defender portal that mirror your existing Sentinel permissions. Test with a pilot group before org-wide rollout. Keep workspace RBAC roles for 30 days as a fallback. Gotcha 5: Automation Rules Don't Auto-Migrate Sentinel automation rules and playbooks don't carry over to the Defender portal automatically. The syntax has changed, and not all Sentinel automation actions are available in Defender. Recommended approach: Export existing Sentinel automation rules (screenshot condition logic and actions) Recreate them in the Defender portal Run both in parallel for one week to validate behavior Retire Sentinel automation rules only after confirming Defender equivalents work correctly Practical Migration Timeline Phase 1 - Pre-migration (1-2 weeks before): Audit connectors, analytics rules, RBAC roles, and automation rules Document everything - titles, GUIDs, permissions, automation logic Test in a pilot environment first Phase 2 - Cutover day: Connect workspace to Defender portal Within 2 hours: audit auto-enabled connectors Within 4 hours: check for duplicate incidents Within 24 hours: validate RBAC and automation rules Phase 3 - Post-migration (1-2 weeks after): Monitor incident volume for duplication spikes Validate automation rules fire correctly Collect SOC team feedback on workflow impact After 1 week of stability: retire legacy automation rules Phase 4 - Cleanup (2-4 weeks after): Remove duplicate automation rules Archive workspace-specific RBAC roles once unified RBAC is stable Update SOC runbooks and documentation The bottom line: treat this as a parallel-run migration, not a lift-and-shift. Budget 2 weeks for parallel operations. Teams that rushed this transition consistently reported longer MTTR during the first month post-migration.Security baseline for Windows Server 2025, version 2602
Microsoft is pleased to announce the February 2026 Revision (v2602) of the security baseline package for Windows Server 2025! You can download the baseline package from the Microsoft Security Compliance Toolkit, test the recommended configurations in your environment, and customize / implement them as appropriate. Summary of Changes in This Release This release includes several changes made since the Security baseline for Windows Server 2025, version 2506 to further assist in the security of enterprise customers along with better aligning with the latest capabilities and standards. The changes include what is now depicted in the table below. Security Policy Change Summary Configure the behavior of the sudo command Configured as Enabled: Disabled on both MS and DC Configure Validation of ROCA-vulnerable WHfB keys during authentication Configured as Enabled: Block on DC to block Windows Hello for Business (WHfB) keys that are vulnerable to the Return of Coppersmith's attack (ROCA) Disable Internet Explorer 11 Launch Via COM Automation Configured as Enabled to prevent legacy scripts and applications from programmatically launching Internet Explorer 11 using COM automation interfaces Do not apply the Mark of the Web tag to files copied from insecure sources Configured as Disabled on both MS and DC Network security: Restrict NTLM: Audit Incoming NTLM Traffic Configured as Enable auditing for all accounts on both MS and DC Network security: Restrict NTLM: Audit NTLM authentication in this domain Configured as Enable all on DC Network security: Restrict NTLM: Outgoing NTLM traffic to remote servers Configured as Audit all on both MS and DC NTLM Auditing Enhancements Already enabled by default to improve visibility into NTLM usage within your environment Prevent downloading of enclosures Remove from the baseline as it is not applicable for Windows Server 2025. It depends on IE – RSS feed Printer: Configure RPC connection settings Enforce the default, RPC over TCP with Authentication Enabled, on both MS and DC Printer: Configure RPC listener settings Configure as RPC over TCP | Kerberos on MS Printer: Impersonate a client after authentication Add RESTRICTED SERVICES\PrintSpoolerService to allow the Print Spooler’s restricted service identity to impersonate clients securely Configure the behavior of the sudo command Sudo for Windows can be used as a potential escalation of privilege vector when enabled in certain configurations. It may allow attackers or malicious insiders to run commands with elevated privileges, bypassing traditional UAC prompts. This is especially concerning in environments with Active Directory or domain controllers. We recommend to configuring the policy Configure the behavior of the sudo command (System) as Enabled with the maximum allowed sudo mode as Disabled to prevent the sudo command from being used. Configure Validation of ROCA-vulnerable WHfB keys during authentication To mitigate Windows Hello for Business (WHfB) keys that are vulnerable to the Return of Coppersmith's attack (ROCA), we recommend enabling the setting Configure Validation of ROCA-vulnerable WHfB keys during authentication (System\Security Account Manager) in a Block mode in domain controllers. To ensure there are no incompatible devices/orphaned/vulnerable keys in use that will break when blocked, please see Using WHfBTools PowerShell module for cleaning up orphaned Windows Hello for Business Keys - Microsoft Support. Note: A reboot is not required for changes to this setting to take effect. Disable Internet Explorer 11 Launch Via COM Automation Similar to the Windows 11 version 25H2 security baseline, we recommend disabling Internet Explorer 11 Launch Via COM Automation (Windows Components\Internet Explorer) to prevent legacy scripts and applications from programmatically launching Internet Explorer 11 using COM automation interfaces such as CreateObject("InternetExplorer.Application"). Allowing such behavior poses a significant risk by exposing systems to the legacy MSHTML and ActiveX components, which are vulnerable to exploitation. Do not apply the Mark of the Web tag to files copied from insecure sources We have included the setting Do not apply the Mark of the Web tag to files copied from insecure sources (Windows Components\File Explorer) configured as Disabled, which is consistent with Windows 11 security baseline. When this configuration is set to Disabled, Windows applies the Mark of the Web (MotW) tag to files copied from locations classified as Internet or other untrusted zones. This tag helps enforce additional protections such as SmartScreen checks and Office macro blocking, reducing the risk of malicious content execution. NTLM Auditing As part of our ongoing effort to help customers transition away from NTLM and adopt Kerberos for a more secure environment, we introduce new recommendations to strengthen monitoring and prepare for future NTLM restrictions on Windows Server 2025. Configure Network security: Restrict NTLM: Audit Incoming NTLM Traffic (Security Options) to Enable auditing for all accounts on both member servers and domain controllers. When enabled, the server logs events for all NTLM authentication requests that would be blocked once incoming NTLM traffic restrictions are enforced. Configure Network security: Restrict NTLM: Audit NTLM authentication in this domain (Security Options) to Enable all on domain controllers. This setting logs NTLM pass-through authentication requests from servers and accounts that would be denied when NTLM authentication restrictions are applied at the domain level. Configure Outgoing NTLM traffic to remote servers (Security Options) to Audit all on both member servers and domain controllers to log an event for each NTLM authentication request sent to a remote server, helping identify servers that still receive NTLM traffic. In addition, there are two new NTLM auditing capabilities enabled by default that were recently introduced in Windows Server 2025 and Windows 11 version 25H2. These enhancements provide detailed audit logs to help security teams monitor and investigate authentication activity, identify insecure practices, and prepare for future NTLM restrictions. Since these auditing improvements are enabled by default, no additional configuration is required, and thus the baseline does not explicitly enforce them. For more details, see Overview of NTLM auditing enhancements in Windows 11 and Windows Server 2025. Prevent Downloading of Enclosures The policy Prevent downloading of enclosures (Windows Components\RSS Feeds) has been removed from the Windows Server 2025 security baseline. This setting is not applicable to Windows Server 2025 because it depends on Internet Explorer functionality for RSS feeds. Printer security enhancements There are two new policies in Windows Server 2025 designed to significantly improve security posture of printers: Require IPPS for IPP printers (Printers) Set TLS/SSL security policy for IPP printers (Printers) Enabling these policies may cause operational challenges in environments that still rely on IPP or use self-signed or locally issued certificates. For this reason, these policies are not ter enforced in the Windows Server 2025 security baseline. However, we do recommend customers transition out of IPP or self-signed certificates and restricting them for a more secure environment. In addition, there are some changes to printer security Added RESTRICTED SERVICES\PrintSpoolerServiceto the Impersonate a client after authentication (User Rights Assignments) policy for both member servers and domain controllers, consistent with security baseline for Windows 11 version 25H2. Enforced the default setting for Configure RPC connection settings (Printers) to always use RPC over TCP with Authentication Enabled on both member servers and domain controllers. This prevents misconfiguration that could introduce security risks. Raised the security bar of the policy Configure RPC listener settings (Printers) from Negotiate (default) to Kerberos on member servers. This change encourages customers to move away from NTLM and adopt Kerberos for a more secure environment. Secure Boot certificate update To help organizations deploy, manage, and monitor the Secure Boot certificate update, Windows includes several policy settings under Administrative Templates\Windows Components\Secure Boot. These settings are deployment controls and aids. Enable Secure Boot Certificate Deployment allows an organization to explicitly initiate certificate deployment on a device. When enabled, Windows begins the Secure Boot certificate update process the next time the Secure Boot task runs. This setting does not override firmware compatibility checks or force updates onto unsupported devices. Automatic Certificate Deployment via Updates controls whether Secure Boot certificate updates are applied automatically through monthly Windows security and non‑security updates. By default, devices that Microsoft has identified as capable of safely applying the updates will receive and apply them automatically as part of cumulative servicing. If this setting is disabled, automatic deployment is blocked and certificate updates must be initiated through other supported deployment methods. Certificate Deployment via Controlled Feature Rollout allows organizations to opt devices into a Microsoft‑managed Controlled Feature Rollout for Secure Boot certificate updates. When enabled, Microsoft assists with coordinating deployment across enrolled devices to reduce risk during rollout. Devices participating in a Controlled Feature Rollout must have diagnostic data enabled. Devices that are not enrolled will not participate. Secure Boot certificate updates depend on device firmware support. Some devices have known firmware limitations that can prevent updates from being applied safely. Organizations should test representative hardware, monitor Secure Boot event logs, and consult the deployment guidance at https://aka.ms/GetSecureBoot for detailed recommendations and troubleshooting information. SMB Server hardening feature SMB Server has been susceptible to relay attacks (e.g., CVE-2025-55234), and Microsoft has released multiple features to protect against the relay attacks including SMB Server signing, which can be enabled with the setting of Microsoft network server: Digitally sign communications (always) (Security Option) SMB Server extended protection for authentication (EPA), which can be enabled with the setting of Microsoft network server: Server SPN target name validation level (Security Option) To further support customers to adopt these SMB Server hardening features, in the September 2025 Security Updates, Microsoft has released support for Audit events, across all supported in-market platforms, to audit SMB client compatibility for SMB Server signing as well as SMB Server EPA. These audit capabilities can be controlled via the two policies located at Network\Lanman Server Audit client does not support signing Audit SMB client SPN support This allows you to identify any potential device or software incompatibility issues before deploying the hardening measures that are already supported by SMB Server. Our recommendation is For domain controllers, the SMB signing is already enabled by default so there is no action needed for hardening purposes. For member servers, first enabling the two new audit features to assess the environment and then decide whether SMB Server Signing or EPA should be used to mitigate the attack vector. Please let us know your thoughts by commenting on this post or through the Security Baseline Community.Windows 11, version 25H2 security baseline
Microsoft is pleased to announce the security baseline package for Windows 11, version 25H2! You can download the baseline package from the Microsoft Security Compliance Toolkit, test the recommended configurations in your environment, and customize / implement them as appropriate. Summary of changes This release includes several changes made since the Windows 11, version 24H2 security baseline to further assist in the security of enterprise customers, to include better alignment with the latest capabilities and standards. The changes include what is depicted in the table below. Security Policy Change Summary Printer: Impersonate a client after authentication Add “RESTRICTED SERVICES\PrintSpoolerService” to allow the Print Spooler’s restricted service identity to impersonate clients securely NTLM Auditing Enhancements Enable by default to improve visibility into NTLM usage within your environment MDAV: Attack Surface Reduction (ASR) Add "Block process creations originating from PSExec and WMI commands" (d1e49aac-8f56-4280-b9ba-993a6d77406c) with a recommended value of 2 (Audit) to improve visibility into suspicious activity MDAV: Control whether exclusions are visible to local users Move to Not Configured as it is overridden by the parent setting MDAV: Scan packed executables Remove from the baseline because the setting is no longer functional - Windows always scans packed executables by default Network: Configure NetBIOS settings Disable NetBIOS name resolution on all network adapters to reduce legacy protocol exposure Disable Internet Explorer 11 Launch Via COM Automation Disable to prevent legacy scripts and applications from programmatically launching Internet Explorer 11 using COM automation interfaces Include command line in process creation events Enable to improve visibility into how processes are executed across the system WDigest Authentication Remove from the baseline because the setting is obsolete - WDigest is disabled by default and no longer needed in modern Windows environments Printer Improving Print Security with IPPS and Certificate Validation To enhance the security of network printing, Windows introduces two new policies focused on controlling the use of IPP (Internet Printing Protocol) printers and enforcing encrypted communications. The setting, "Require IPPS for IPP printers", (Administrative Templates\Printers) determines whether printers that do not support TLS are allowed to be installed. When this policy is disabled (default), both IPP and IPPS transport printers can be installed - although IPPS is preferred when both are available. When enabled, only IPPS printers will be installed; attempts to install non-compliant printers will fail and generate an event in the Application log, indicating that installation was blocked by policy. The second policy, "Set TLS/SSL security policy for IPP printers" (same policy path) requires that printers present valid and trusted TLS/SSL certificates before connections can be established. Enabling this policy defends against spoofed or unauthorized printers, reducing the risk of credential theft or redirection of sensitive print jobs. While these policies significantly improve security posture, enabling them may introduce operational challenges in environments where IPP and self-signed or locally issued certificates are still commonly used. For this reason, neither policy is enforced in the security baseline, at this time. We recommend that you assess your printers, and if they meet the requirements, consider enabling those policies with a remediation plan to address any non-compliant printers in a controlled and predictable manner. User Rights Assignment Update: Impersonate a client after authentication We have added RESTRICTED SERVICES\PrintSpoolerService in the “Impersonate a client after authentication” User Rights Assignment policy. The baseline already includes Administrators, SERVICE, LOCAL SERVICE, and NETWORK SERVICE for this user right. Adding the restricted Print Spooler supports Microsoft’s ongoing effort to apply least privilege to system services. It enables Print Spooler to securely impersonate user tokens in modern print scenarios using a scoped, restricted service identity. Although this identity is associated with functionality introduced as part of Windows Protected Print (WPP), it is required to support proper print operations even if WPP is not currently enabled. The system manifests the identity by default, and its presence ensures forward compatibility with WPP-based printing. Note: This account may appear as a raw SID (e.g., S-1-5-99-...) in Group Policy or local policy tools before the service is fully initialized. This is expected and does not indicate a misconfiguration. Warning: Removing this entry will result in print failures in environments where WPP is enabled. We recommend retaining this entry in any custom security configuration that defines this user right. NTLM Auditing Enhancements Windows 11, version 25H2 includes enhanced NTLM auditing capabilities, enabled by default, which significantly improves visibility into NTLM usage within your environment. These enhancements provide detailed audit logs to help security teams monitor and investigate authentication activity, identify insecure practices, and prepare for future NTLM restrictions. Since these auditing improvements are enabled by default, no additional configuration is required, and thus the baseline does not explicitly enforce them. For more details, see Overview of NTLM auditing enhancements in Windows 11 and Windows Server 2025. Microsoft Defender Antivirus Attack Surface Reduction (ASR) In this release, we've updated the Attack Surface Reduction (ASR) rules to add the policy Block process creations originating from PSExec and WMI commands (d1e49aac-8f56-4280-b9ba-993a6d77406c) with a recommended value of 2 (Audit). By auditing this rule, you can gain essential visibility into potential privilege escalation attempts via tools such as PSExec or persistence mechanisms using WMI. This enhancement helps organizations proactively identify suspicious activities without impacting legitimate administrative workflows. Control whether exclusions are visible to local users We have removed the configuration for the policy "Control whether exclusions are visible to local users" (Windows Components\Microsoft Defender Antivirus) from the baseline in this release. This change was made because the parent policy "Control whether or not exclusions are visible to Local Admins" is already set to Enabled, which takes precedence and effectively overrides the behavior of the former setting. As a result, explicitly configuring the child policy is unnecessary. You can continue to manage exclusion visibility through the parent policy, which provides the intended control over whether local administrators can view exclusion lists. Scan packed executables The “Scan packed executables” setting (Windows Components\Microsoft Defender Antivirus\Scan) has been removed from the security baseline because it is no longer functional in modern Windows releases. Microsoft Defender Antivirus always scans packed executables by default, therefore configuring this policy has no effect on the system. Disable NetBIOS Name Resolution on All Networks In this release, we start disabling NetBIOS name resolution on all network adapters in the security baseline, including those connected to private and domain networks. The change is reflected in the policy setting “Configure NetBIOS settings” (Network\DNS Client). We are trying to eliminate the legacy name resolution protocol that is vulnerable to spoofing and credential theft. NetBIOS is no longer needed in modern environments where DNS is fully deployed and supported. To mitigate potential compatibility issues, you should ensure that all internal systems and applications use DNS for name resolution. We recommend the following; test critical workflows in a staging environment prior to deployment, monitor for any resolution failures or fallback behavior, and inform support staff of the change to assist with troubleshooting as needed. This update aligns with our broader efforts to phase out legacy protocols and improve security. Disable Internet Explorer 11 Launch Via COM Automation To enhance the security posture of enterprise environments, we recommend disabling Internet Explorer 11 Launch Via COM Automation (Windows Components\Internet Explorer) to prevent legacy scripts and applications from programmatically launching Internet Explorer 11 using COM automation interfaces such as CreateObject("InternetExplorer.Application"). Allowing such behavior poses a significant risk by exposing systems to the legacy MSHTML and ActiveX components, which are vulnerable to exploitation. Include command line in process creation events We have enabled the setting "Include command line in process creation events" (System\Audit Process Creation) in the baseline to improve visibility into how processes are executed across the system. Capturing command-line arguments allows defenders to detect and investigate malicious activity that may otherwise appear legitimate, such as abuse of scripting engines, credential theft tools, or obfuscated payloads using native binaries. This setting supports modern threat detection techniques with minimal performance overhead and is highly recommended. WDigest Authentication We removed the policy "WDigest Authentication (disabling may require KB2871997)" from the security baseline because it is no longer necessary for Windows. This policy was originally enforced to prevent WDigest from storing user’s plaintext passwords in memory, which posed a serious credential theft risk. However, starting with 24H2 update, the engineering teams deprecated this policy. As a result, there is no longer a need to explicitly enforce this setting, and the policy has been removed from the baseline to reflect the current default behavior. Since the setting does not write to the normal policies location in the registry it will not be cleaned up automatically for any existing deployments. Please let us know your thoughts by commenting on this post or through the Security Baseline Community.Protect and govern every tenant with Microsoft Entra Tenant Governance
This event will no longer take place on July 1. Please follow this page to be notified of the new date and time once scheduled. As organizations scale, tenant sprawl becomes inevitable. Legacy test tenants, employee‑created environments, and forgotten tenants create blind spots for security and identity teams. Get to know Microsoft Entra Tenant Governance, a new Entra capability that provides centralized visibility and control across multi‑tenant environments. We'll cover how Tenant Governance enables tenant discovery, secure governance relationships, configuration monitoring, and governed tenant creation from day one. You'll see how organizations can apply consistent security baselines, detect configuration drift, and reduce operational overhead all while maintaining autonomy across teams. Walk away with a clear framework for bringing order, visibility, and governance to your multi‑tenant identity landscape. How do I participate? Registration is not required. Add this event to your calendar, then sign in to the Tech Community and select Attend to receive reminders. Post your questions in advance, or any time during the live broadcast.Windows 11 24H2 Sec Baseline → Broken SSO to on‑prem (Root cause: PKINIT SHA‑1 baseline)
Hi all, I ran into an issue with Entra-joined devices using Windows Hello for Business (Cloud Kerberos Trust) that might help others working with Windows 11 24H2 security baselines. Scenario Windows 11 25H2 devices Entra-joined (not hybrid) Intune-managed Windows Hello for Business (WHfB) enabled Cloud Kerberos Trust configured On-prem AD (Windows Server 2019/2022 DCs) Access to SMB shares / on-prem applications Symptoms SSO to on-prem resources fails Users get credential/PIN prompt instead of SSO Error message: “The system cannot contact a domain controller to service the authentication request” Client-side observations: klist → no tickets (initially) After enabling Cloud Kerberos Trust: klist get krbtgt → works klist get cifs/server.domain → fails Error: 0xc000a100 / 0x3bc4 Hash generation for the specified version and hash type is not enabled on server Root Cause The issue was caused by a Windows 11 24H2 security baseline setting related to Kerberos/PKINIT. The 24H2 baseline introduces a policy for configuring hash algorithms for certificate-based Kerberos authentication (PKINIT). This setting allows environments to disable SHA-1 and require SHA-2 algorithms. [applepie.se] Important detail: This configuration only works if the domain controllers fully support PKINIT with SHA-2, which effectively requires Windows Server 2025 domain controllers across the environment. If SHA-1 is disabled while running: Windows Server 2019 or 2022 DCs Mixed environments then PKINIT authentication fails, which directly impacts: Windows Hello for Business Cloud Kerberos Trust Any passwordless Kerberos-based authentication Why this is difficult to troubleshoot Cloud Kerberos Trust appears correctly configured AzureADKerberos object exists PRT is valid Network connectivity is fine However: Kerberos tickets are not issued correctly Service tickets (CIFS, HTTP, etc.) fail Errors are misleading and point to KDC/hash issues No explicit warning is provided in baseline guidance that mixed environments will break Resolution Revert the baseline change and allow SHA-1 for PKINIT again. Policy location: Computer Configuration → System → Kerberos / KDC → Configure hash algorithms for certificate logon Ensure: SHA-1 is set to Allowed/Default After reverting: Kerberos ticket issuance works SSO to on-prem resources is restored Recommendation Do not disable SHA-1 for PKINIT unless: All domain controllers are Windows Server 2025, and PKINIT SHA-2 support has been fully validated Treat this setting as future hardening, not production-safe for mixed environments today. Takeaway If you experience: WHfB + Cloud Kerberos Trust SSO failures klist get errors with hash generation issues Missing or failing Kerberos service tickets check the PKINIT hash configuration from the 24H2 security baseline first.Kerberos and the End of RC4: Protocol Hardening and Preparing for CVE‑2026‑20833
CVE-2026-20833 addresses the continued use of the RC4‑HMAC algorithm within the Kerberos protocol in Active Directory environments. Although RC4 has been retained for many years for compatibility with legacy systems, it is now considered cryptographically weak and unsuitable for modern authentication scenarios. As part of the security evolution of Kerberos, Microsoft has initiated a process of progressive protocol hardening, whose objective is to eliminate RC4 as an implicit fallback, establishing AES128 and AES256 as the default and recommended algorithms. This change should not be treated as optional or merely preventive. It represents a structural change in Kerberos behavior that will be progressively enforced through Windows security updates, culminating in a model where RC4 will no longer be implicitly accepted by the KDC. If Active Directory environments maintain service accounts, applications, or systems dependent on RC4, authentication failures may occur after the application of the updates planned for 2026, especially during the enforcement phases introduced starting in April and finalized in July 2026. For this reason, it is essential that organizations proactively identify and eliminate RC4 dependencies, ensuring that accounts, services, and applications are properly configured to use AES128 or AES256 before the definitive changes to Kerberos protocol behavior take effect. Official Microsoft References CVE-2026-25177 - Security Update Guide - Microsoft - Active Directory Domain Services Elevation of Privilege Vulnerability Microsoft Support – How to manage Kerberos KDC usage of RC4 for service account ticket issuance changes related to CVE-2026-20833 (KB 5073381) Microsoft Learn – Detect and Remediate RC4 Usage in Kerberos AskDS – What is going on with RC4 in Kerberos? Beyond RC4 for Windows authentication | Microsoft Windows Server Blog So, you think you’re ready for enforcing AES for Kerberos? | Microsoft Community Hub Risk Associated with the Vulnerability When RC4 is used in Kerberos tickets, an authenticated attacker can request Service Tickets (TGS) for valid SPNs, capture these tickets, and perform offline brute-force attacks, particularly Kerberoasting scenarios, with the goal of recovering service account passwords. Compared to AES, RC4 allows significantly faster cracking, especially for older accounts or accounts with weak passwords. Technical Overview of the Exploitation In simplified terms, the exploitation flow occurs as follows: The attacker requests a TGS for a valid SPN. The KDC issues the ticket using RC4, when that algorithm is still accepted. The ticket is captured and analyzed offline. The service account password is recovered. The compromised account is used for lateral movement or privilege escalation. Official Timeline Defined by Microsoft Important clarification on enforcement behavior Explicit account encryption type configurations continue to be honored even during enforcement mode. The Kerberos hardening associated with CVE‑2026‑20833 focuses on changing the default behavior of the KDC, enforcing AES-only encryption for TGS ticket issuance when no explicit configuration exists. This approach follows the same enforcement model previously applied to Kerberos session keys in earlier security updates (for example, KB5021131 related to CVE‑2022‑37966), representing another step in the progressive removal of RC4 as an implicit fallback. January 2026 – Audit Phase Starting in January 2026, Microsoft initiated the Audit Phase related to changes in RC4 usage within Kerberos, as described in the official guidance associated with CVE-2026-20833. The primary objective of this phase is to allow organizations to identify existing RC4 dependencies before enforcement changes are applied in later phases. During this phase, no functional breakage is expected, as RC4 is still permitted by the KDC. However, additional auditing mechanisms were introduced, providing greater visibility into how Kerberos tickets are issued in the environment. Analysis is primarily based on the following events recorded in the Security Log of Domain Controllers: Event ID 4768 – Kerberos Authentication Service (AS request / Ticket Granting Ticket) Event ID 4769 – Kerberos Service Ticket Operations (Ticket Granting Service – TGS) Additional events related to the KDCSVC service These events allow identification of: the account that requested authentication the requested service or SPN the source host of the request the encryption algorithm used for the ticket and session key This information is critical for detecting scenarios where RC4 is still being implicitly used, enabling operations teams to plan remediation ahead of the enforcement phase. If these events are not being logged on Domain Controllers, it is necessary to verify whether Kerberos auditing is properly enabled. For Kerberos authentication events to be recorded in the Security Log, the corresponding audit policies must be configured. The minimum recommended configuration is to enable Success auditing for the following subcategories: Kerberos Authentication Service Kerberos Service Ticket Operations Verification can be performed directly on a Domain Controller using the following commands: auditpol /get /subcategory:"Kerberos Service Ticket Operations" auditpol /get /subcategory:"Kerberos Authentication Service" In enterprise environments, the recommended approach is to apply this configuration via Group Policy, ensuring consistency across all Domain Controllers. The corresponding policy can be found at: Computer Configuration - Policies - Windows Settings - Security Settings - Advanced Audit Policy Configuration - Audit Policies - Account Logon Once enabled, these audits record events 4768 and 4769 in the Domain Controllers’ Security Log, allowing analysis tools—such as inventory scripts or SIEM/Log Analytics queries—to accurately identify where RC4 is still present in the Kerberos authentication flow. April 2026 – Enforcement with Manual Rollback With the April 2026 update, the KDC begins operating in AES-only mode (0x18) when the msDS-SupportedEncryptionTypes attribute is not defined. This means RC4 is no longer accepted as an implicit fallback. During this phase, applications, accounts, or computers that still implicitly depend on RC4 may start failing. Manual rollback remains possible via explicit configuration of the attribute in Active Directory. July 2026 – Final Enforcement Starting in July 2026, audit mode and rollback options are removed. RC4 will only function if explicitly configured—a practice that is strongly discouraged. This represents the point of no return in the hardening process. Official Monitoring Approach Microsoft provides official scripts in the repository: https://github.com/microsoft/Kerberos-Crypto/tree/main/scripts The two primary scripts used in this analysis are: Get-KerbEncryptionUsage.ps1 The Get-KerbEncryptionUsage.ps1 script, provided by Microsoft in the Kerberos‑Crypto repository, is designed to identify how Kerberos tickets are issued in the environment by analyzing authentication events recorded on Domain Controllers. Data collection is primarily based on: Event ID 4768 – Kerberos Authentication Service (AS‑REQ / TGT issuance) Event ID 4769 – Kerberos Service Ticket Operations (TGS issuance) From these events, the script extracts and consolidates several relevant fields for authentication flow analysis: Time – when the authentication occurred Requestor – IP address or host that initiated the request Source – account that requested the ticket Target – requested service or SPN Type – operation type (AS or TGS) Ticket – algorithm used to encrypt the ticket SessionKey – algorithm used to protect the session key Based on these fields, it becomes possible to objectively identify which algorithms are being used in the environment, both for ticket issuance and session establishment. This visibility is essential for detecting RC4 dependencies in the Kerberos authentication flow, enabling precise identification of which clients, services, or accounts still rely on this legacy algorithm. Example usage: .\Get-KerbEncryptionUsage.ps1 -Encryption RC4 -Searchscope AllKdcs | Export-Csv -Path .\KerbUsage_RC4_All_ThisDC.csv -NoTypeInformation -Encoding UTF8 Data Consolidation and Analysis In enterprise environments, where event volumes may be high, it is recommended to consolidate script results into analytical tools such as Power BI to facilitate visualization and investigation. The presented image illustrates an example dashboard built from collected results, enabling visibility into: Total events analyzed Number of Domain Controllers involved Number of requesting clients (Requestors) Most frequently involved services or SPNs (Targets) Temporal distribution of events RC4 usage scenarios (Ticket, SessionKey, or both) This type of visualization enables rapid identification of RC4 usage patterns, remediation prioritization, and progress tracking as dependencies are eliminated. Additionally, dashboards help answer key operational questions, such as: Which services still depend on RC4 Which clients are negotiating RC4 for sessions Which Domain Controllers are issuing these tickets Whether RC4 usage is decreasing over time This combined automated collection + analytical visualization approach is the recommended strategy to prepare environments for the Microsoft changes related to CVE‑2026‑20833 and the progressive removal of RC4 in Kerberos. Visualizing Results with Power BI To facilitate analysis and monitoring of RC4 usage in Kerberos, it is recommended to consolidate script results into a Power BI analytical dashboard. 1. Install Power BI Desktop Download and install Power BI Desktop from the official Microsoft website 2. Execute data collection After running the Get-KerbEncryptionUsage.ps1 script, save the generated CSV file to the following directory: C:\Temp\Kerberos_KDC_usage_of_RC4_Logs\KerbEncryptionUsage_RC4.csv 3. Open the dashboard in Power BI Open the file RC4-KerbEncryptionUsage-Dashboards.pbix using Power BI Desktop. If you are interested, please leave a comment on this post with your email address, and I will be happy to share with you. 4. Update the data source If the CSV file is located in a different directory, it will be necessary to adjust the data source path in Power BI. As illustrated, the dashboard uses a parameter named CsvFilePath, which defines the path to the collected CSV file. To adjust it: Open Transform Data in Power BI. Locate the CsvFilePath parameter in the list of Queries. Update the value to the directory where the CSV file was saved. Click Refresh Preview or Refresh to update the data. Click Home → Close & Apply. This approach allows rapid identification of RC4 dependencies, prioritization of remediation actions, and tracking of progress throughout the elimination process. List-AccountKeys.ps1 This script is used to identify which long-term keys are present on user, computer, and service accounts, enabling verification of whether RC4 is still required or whether AES128/AES256 keys are already available. Interpreting Observed Scenarios Microsoft recommends analyzing RC4 usage by jointly considering two key fields present in Kerberos events: Ticket Encryption Type Session Encryption Type Each combination represents a distinct Kerberos behavior, indicating the source of the issue, risk level, and remediation point in the environment. In addition to events 4768 and 4769, updates released starting January 13, 2026, introduce new Kdcsvc events in the System Event Log that assist in identifying RC4 dependencies ahead of enforcement. These events include: Event ID 201 – RC4 usage detected because the client advertises only RC4 and the service does not have msDS-SupportedEncryptionTypes defined. Event ID 202 – RC4 usage detected because the service account does not have AES keys and the msDS-SupportedEncryptionTypes attribute is not defined. Event ID 203 – RC4 usage blocked (enforcement phase) because the client advertises only RC4 and the service does not have msDS-SupportedEncryptionTypes defined. Event ID 204 – RC4 usage blocked (enforcement phase) because the service account does not have AES keys and msDS-SupportedEncryptionTypes is not defined. Event ID 205 – Detection of explicit enablement of insecure algorithms (such as RC4) in the domain policy DefaultDomainSupportedEncTypes. Event ID 206 – RC4 usage detected because the service accepts only AES, but the client does not advertise AES support. Event ID 207 – RC4 usage detected because the service is configured for AES, but the service account does not have AES keys. Event ID 208 – RC4 usage blocked (enforcement phase) because the service accepts only AES and the client does not advertise AES support. Event ID 209 – RC4 usage blocked (enforcement phase) because the service accepts only AES, but the service account does not have AES keys. https://support.microsoft.com/en-gb/topic/how-to-manage-kerberos-kdc-usage-of-rc4-for-service-account-ticket-issuance-changes-related-to-cve-2026-20833-1ebcda33-720a-4da8-93c1-b0496e1910dc They indicate situations where RC4 usage will be blocked in future phases, allowing early detection of configuration issues in clients, services, or accounts. These events are logged under: Log: System Source: Kdcsvc Below are the primary scenarios observed during the analysis of Kerberos authentication behavior, highlighting how RC4 usage manifests across different ticket and session encryption combinations. Each scenario represents a distinct risk profile and indicates specific remediation actions required to ensure compliance with the upcoming enforcement phases. Scenario A – RC4 / RC4 In this scenario, both the Kerberos ticket and the session key are issued using RC4. This is the worst possible scenario from a security and compatibility perspective, as it indicates full and explicit dependence on RC4 in the authentication flow. This condition significantly increases exposure to Kerberoasting attacks, since RC4‑encrypted tickets can be subjected to offline brute-force attacks to recover service account passwords. In addition, environments remaining in this state have a high probability of authentication failure after the April 2026 updates, when RC4 will no longer be accepted as an implicit fallback by the KDC. Events Associated with This Scenario During the Audit Phase, this scenario is typically associated with: Event ID 201 – Kdcsvc Indicates that: the client advertises only RC4 the service does not have msDS-SupportedEncryptionTypes defined the Domain Controller does not have DefaultDomainSupportedEncTypes defined This means RC4 is being used implicitly. This event indicates that the authentication will fail during the enforcement phase. Event ID 202 – Kdcsvc Indicates that: the service account does not have AES keys the service does not have msDS-SupportedEncryptionTypes defined This typically occurs when: legacy accounts have never had their passwords reset only RC4 keys exist in Active Directory Possible Causes Common causes include: the originating client (Requestor) advertises only RC4 the target service (Target) is not explicitly configured to support AES the account has only legacy RC4 keys the msDS-SupportedEncryptionTypes attribute is not defined Recommended Actions To remediate this scenario: Correctly identify the object involved in the authentication flow, typically: a service account (SPN) a computer account or a Domain Controller computer object Verify whether the object has AES keys available using analysis tools or scripts such as List-AccountKeys.ps1. If AES keys are not present, reset the account password, forcing generation of modern cryptographic keys (AES128 and AES256). Explicitly define the msDS-SupportedEncryptionTypes attribute to enable AES support. Recommended value for modern environments: 0x18 (AES128 + AES256) = 24 As illustrated below, this configuration can be applied directly to the msDS-SupportedEncryptionTypes attribute in Active Directory. AES can also be enabled via Active Directory Users and Computers by explicitly selecting: This account supports Kerberos AES 128 bit encryption This account supports Kerberos AES 256 bit encryption These options ensure that new Kerberos tickets are issued using AES algorithms instead of RC4. Temporary RC4 Usage (Controlled Rollback) In transitional scenarios—during migration or troubleshooting—it may be acceptable to temporarily use: 0x1C (RC4 + AES) = 28 This configuration allows the object to accept both RC4 and AES simultaneously, functioning as a controlled rollback while legacy dependencies are identified and corrected. However, the final objective must be to fully eliminate RC4 before the final enforcement phase in July 2026, ensuring the environment operates exclusively with AES128 and AES256. Scenario B – AES / RC4 In this case, the ticket is protected with AES, but the session is still negotiated using RC4. This typically indicates a client limitation, legacy configuration, or restricted advertisement of supported algorithms. Events Associated with This Scenario During the Audit Phase, this scenario may generate: Event ID 206 Indicates that: the service accepts only AES the client does not advertise AES in the Advertised Etypes In this case, the client is the issue. Recommended Action Investigate the Requestor Validate operating system, client type, and advertised algorithms Review legacy GPOs, hardening configurations, or settings that still force RC4 For Linux clients or third‑party applications, review krb5.conf, keytabs, and Kerberos libraries Scenario C – RC4 / AES Here, the session already uses AES, but the ticket is still issued using RC4. This indicates an implicit RC4 dependency on the Target or KDC side, and the environment may fail once enforcement begins. Events Associated with This Scenario This scenario may generate: Event ID 205 Indicates that the domain has explicit insecure algorithm configuration in: DefaultDomainSupportedEncTypes This means RC4 is explicitly allowed at the domain level. Recommended Action Correct the Target object Explicitly define msDS-SupportedEncryptionTypes with 0x18 = 24 Revalidate new ticket issuance to confirm full migration to AES / AES Conclusion CVE‑2026‑20833 represents a structural change in Kerberos behavior within Active Directory environments. Proper monitoring is essential before April 2026, and the msDS-SupportedEncryptionTypes attribute becomes the primary control point for service accounts, computer accounts, and Domain Controllers. July 2026 represents the final enforcement point, after which there will be no implicit rollback to RC4.
