The JScript scripting engine is an old component that was initially included with Internet Explorer 3.0 in 1996 and was Microsoft's own dialect of the ECMAScript standard (the JavaScript language).

The document exploited an Internet Explorer zero-day vulnerability found within “jscript9.dll,” the JavaScript engine of Internet Explorer, which could be used to deliver malware or malicious ...

Microsoft says that customers can now disable JScript (JScript.dll) execution in Internet Explorer 11 after installing the Windows October 2020 monthly security updates.