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JScript9Legacy scripting engine now enabled by default

Naveen_Shankar's avatar
Naveen_Shankar
Icon for Microsoft rankMicrosoft
Jul 09, 2025

To provide a more secure experience, beginning with Windows 11, version 24H2, JScript9Legacy is enabled by default to handle all scripting processes and operations that previously used JScript. Read on to learn more about frequently asked questions for switching from Jscript to JScriptLegacy and its default in Windows 11, version 24H2.

How is JScript9Legacy better than JScript?

Based on JScript9, the new JScriptLegacy scripting engine offers improved performance and security features. JScript9Legacy is designed to be more compatible with modern web standards, which helps mitigate the risk of cross-site scripting (XSS) and other web-based attacks. The new engine incorporates advanced security features such as improved handling of JavaScript objects and stricter execution policies, which make it harder for malicious scripts to exploit the system. By replacing JScript.dll with JScript9Legacy.dll, the operating system can better defend against a wider range of security threats, ultimately providing a more secure environment for users.

What's the impact of this change on other in-market versions of Windows?

There is no impact on Windows versions earlier than 24H2. This change is limited to Windows 11, version 24H2 and above. All scripting processes that rely on JScript in Windows versions earlier than Windows 11, version 24H2 will continue to run as they have.

Are there any additional steps needed to take advantage of JScript9Legacy?

No additional action is required from you to benefit from JScript9Legacy, nor will it impact existing workflows.

If there are incompatibility issues with JScript9Legacy, how does one roll back to JScript?

Please connect with our support team through Services Hub for guidance on rolling back to JScript.

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Updated Jul 09, 2025
Version 1.0
security
windows 11

1 Comment

  • omix's avatar
    omix
    Copper Contributor
    Sep 01, 2025

    Microsoft has finally put a clear name on what it has been doing quietly for years: killing Classic ASP.

    With the latest update, the “JScript9Legacy scripting engine” has been enabled by default, and the result is obvious: applications that have run flawlessly for decades are now broken overnight.

    Before this update, there was no proper warning, no official guidance, no migration plan. All you see is this error:

    Active Server Pages error 'ASP 0240' Script Engine Exception
A ScriptEngine threw exception 'C0000005' in 
'IActiveScript::SetScriptState()' from 
'CActiveScriptEngine::ReuseEngine()'.

    This looks very much like a deliberate “push ASP users into the Linux + PHP ecosystem” operation. For companies still running critical business processes on Classic ASP—often with thousands of pages and millions of lines of code—what else does this mean other than “migrate or die”?

    For those looking for a temporary workaround, there’s a discussion here: https://stackoverflow.com/questions/79650440/windows-11-update-classic-asp-incompatibility-vbscript-jscript-mix-causes-iact .

    But who knows how long such patches will survive. The reality is, Microsoft seems to have made a strategic decision to pull the plug on ASP.

    Trusting the Microsoft ecosystem again to keep your product alive might be the bigger mistake.