Starting with Windows 11 version 24H2, the JScript9Legacy engine will be enabled by default for all scripting processes that previously used the classic JScript engine.
This was announced by Naveen Shankar, Program Manager at Microsoft, in a blog post. The change ensures a more secure user experience and marks the definitive end of JScript as the standard within the Windows platform.
In an explanation, Shankar explains that JScript9Legacy is based on JScript9 and designed with modern web standards and stricter security principles in mind. The new engine offers better protection against common threats. Think of cross-site scripting (XSS) and other forms of web-based attacks. In addition, the performance improvement over the original engine is an important added value. By replacing the outdated jscript.dll with jscript9legacy.dll, the operating system can defend itself more effectively against a wide range of security risks.
Shankar points out that no action is required from users. Existing script tasks will continue to function normally, and no changes to workflows are necessary. In the unlikely event of a compatibility issue, organizations can obtain support from Microsoft’s Services Hub to temporarily revert to the old engine.
The switch represents an important moment in the retirement of JScript. It had been part of Windows since 1996. The engine, Microsoft’s own implementation of ECMAScript, was widely used in Internet Explorer at the time. It also served as the basis for automating tasks in Windows. In the current context, however, JScript is considered obsolete. The engine does not meet today’s JavaScript security standards and was increasingly being exploited for vulnerabilities, including memory corruption and arbitrary code execution via malicious documents or emails.
No reason for further support
According to Microsoft, JScript has been retained until now primarily for backward compatibility. However, with Internet Explorer now officially phased out and the Edge browser widely accepted, the company sees no reason to continue supporting the old engine. JScript9Legacy is not only more secure, but also more flexible in terms of deployment, both within and outside the browser context.
The change applies exclusively to Windows 11 version 24H2 and later versions. Older Windows versions will continue to use the original JScript engine as before.
With this step, Microsoft is emphasizing its focus on security without immediately phasing out legacy scripts. Shankar emphasizes in his blog that JScript9Legacy offers the best of both worlds: greater protection against modern threats while maintaining support for existing applications.