Microsoft announced that it has replaced the default JScript scripting engine with the newer and more secure JScript9Legacy in Windows 11, version 24H2 and later.
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This decision was made due to security concerns, as JScript9Legacy is expected to offer better protection against online threats, such as cross-site scripting (XSS) attacks, as well as improved performance. JScript (jscript.dll), introduced in 1996, is Microsoft's implementation of ECMAScript, similar to JavaScript, and was used primarily in Internet Explorer as well as as a scripting language for automating Windows tasks, validating forms, or creating administrative scripts.
This particular engine is currently considered outdated, incompatible with modern JavaScript security standards, and is a frequent target for attacks that include memory corruption, arbitrary code execution, and XSS vulnerabilities, which can be triggered through malicious documents, emails, and web pages.
Despite its outdated nature, JScript has remained the default engine on Windows to this day, in order to ensure compatibility with older systems and avoid problems in critical workflows.
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However, with the retirement of Internet Explorer and the widespread adoption of the Edge browser, Microsoft is now pushing the envelope and permanently replacing JScript with JScript9Legacy (jscript9legacy.dll), starting with Windows 11 version 24H2.
The new engine is a modernized version of JScript9, can be used outside of the browser , and is designed to support legacy scripts with greater security and better compatibility.
The transition is automatic without any action required from the user, and existing scripts are expected to continue to function normally.
In case compatibility issues arise, Microsoft says that it is possible to revert to the old machine by contacting the support team.
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The move from legacy JScript to JScript9Legacy is part of Microsoft's overall strategy to modernize its operating system and move away from technologies based on Internet Explorer. Internet Explorer, although officially retired, was still indirectly supported through components such as JScript, mainly for compatibility reasons with legacy corporate or government systems.
Source: bleepingcomputer
