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

JScript is a legacy Microsoft implementation of the ECMAScript language specification in the form of an Active Scripting engine.

To manually edit the registry and disable JScript execution in Internet Explorer for Internet Zone and Restricted Sites Zone, follow these steps:

  1. Click Start, click Run, type regedt32 or regedit, and then click Ok.
  2. To disable JScript execution in Internet Zone, locate the following registry subkey in Registry Editor:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3\140D

    To disable JScript execution in Restricted Sites Zone, locate the following registry subkey in Registry Editor:

    HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\4\140D
     
  3. Right-click the appropriate registry subkey, and then click Modify.
  4. In the Edit DWORD (32-bit) Value dialog box, type 3.
  5. Click OK, and then restart Internet Explorer.

To restrict JScript from executing scripts for emulated applications such as a 32-bit application running on a 64-bit device, follow these steps:

  1. Click Start, click Run, type regedt32 or regedit, and then click Ok.
  2. To disable the emulated application, locate the following registry subkey in Registry Editor:

    HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\Windows\CurrentVersion\Internet Settings\Zones\3\140D
  3. In the appropriate subfolder, create a registry value of type DWORD and name it EnableJScriptMitigation.
  4. In the Edit DWORD (32-bit) Value dialog box, type 1.
  5. Click Ok.

Scripts from MSXML

If you run Windows 8 or Windows 8.1, you must have either the Monthly Rollup (MR) or both the Security-Only (SO) update and the Internet Explorer Cumulative Update (IECU) to use this feature. In addition to enabling the feature by using a feature control key, you must also change the registry keys accordingly to restrict JScript from being loaded through MSXML.

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To restrict JScript from executing scripts from MSXML3 and MSXML6, follow these steps:

  1. Click Start, click Run, type regedt32 or regedit, and then click Ok.
  2. To disable Script execution through MSXML3 and MSXML6, locate the following registry subkey in Registry Editor:

    For x86-based devices
    • For MSXML3: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSXML30
    • For MSXML6: HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\MSXML60
    For x64-based devices
    • For MSXML3: HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\MSXML30
    • For MSXML6: HKEY_LOCAL_MACHINE\SOFTWARE\WOW6432Node\Microsoft\MSXML60
  3. In each appropriate subfolder, create a registry value of type DWORD and name it EnableJScriptMitigation.
  4. In the Edit DWORD (32-bit) Value dialog box, type 1.
  5. Click Ok.