NetworkSignatureInspected

NetworkSignatureInspected is not an execution or connection event. It’s a network inspection telemetry event generated when Microsoft Defender for Endpoint inspects network traffic against known threat signatures (including Zeek-based signatures and Microsoft threat intelligence patterns).

In simple terms, it means traffic was inspected and matched against a signature — not that the device executed or downloaded that content.

The AdditionalFields content you’re seeing is raw or partially decoded network payload that matched a detection signature. In your example, references like CVE-2021-44228, suspicious script fragments, Qakbot indicators, curl.exe strings, and obfuscated JavaScript strongly suggest this was traffic inspected for exploit or malware patterns (likely Log4Shell-related scanning or web-based delivery attempts).

A few important clarifications:

1. NetworkSignatureInspected does not mean successful exploitation. It means traffic matched a signature pattern.
2. If Defender reports no alerts and DeviceNetworkEvents or CommonSecurityLog show no corresponding outbound connections to those domains, this often indicates one of the following:
   • The traffic was blocked upstream.
   • It was passive inspection of inbound scanning traffic.
   • It was signature matching within encrypted or partially reconstructed traffic.
   • The content was embedded in payload inspection but never executed.
3. The presence of CVE-2021-44228 references is very common in internet-wide scanning activity. Many internet-facing services still receive automated exploit probes. If multiple devices show similar entries, it is very likely opportunistic scanning rather than targeted compromise.

The encoded and binary-like segments in AdditionalFields are typical of payload fragments captured during deep packet inspection. They are not meant to be human-readable logs; they are signature-matching artifacts.

If there are:

• No correlated DeviceProcessEvents (e.g., no suspicious child processes)
• No successful outbound connections to the referenced domains
• No Defender alerts tied to the event
• No abnormal authentication or lateral movement activity

Then this is most likely inspection of malicious or suspicious network content that did not result in execution or compromise.

In environments with internet exposure, especially web services, this type of telemetry is normal background noise from automated scanning and botnet activity.

If you want additional confidence, you can pivot on:

• RemoteIP from DeviceNetworkEvents
• Any matching AlertIds
• Correlated DeviceProcessEvents around the same timestamp
• DeviceFileEvents involving curl.exe or regsvr32

But based on what you’ve described, this aligns with expected inspection behavior rather than confirmed compromise.