Microsoft Internet Explorer Scripting Engine Memory Corruption Vulnerability
CVE-2020-0674 is a security vulnerability in Microsoft Internet Explorer, added to CISA KEV on November 3, 2021. Patch priority: Plan to patch.
What it is
Microsoft Internet Explorer contains a memory corruption vulnerability due to the way the Scripting Engine handles objects in memory. Successful exploitation could allow remote code execution in the context of the current user.
VulnCheck tracked exploitation 631 days before CISA's KEV listing. VulnCheck's broader catalog of in-the-wild exploitation evidence picked this up before it landed on CISA's formal list. Per-CVE fact about this entry; not a population claim about lead time in general.
Who's affected
Affects anyone running Microsoft Internet Explorer. Microsoft products in a small practice typically sit close to credentials, email, or document workflows — treat the patch as in-scope.
What to do
Apply updates per vendor instructions.
If you don't have someone in-house to verify the patch deployed across every endpoint — or you're not sure whether you're affected — that's exactly the kind of triage we do. Book a free 20-minute triage call.
Insurance readiness
Your insurer will ask if this is patched.
Unpatched entries on CISA's Known Exploited Vulnerabilities list are exactly what cyber-insurance carrier questionnaires probe for, and knowing which controls they check is how you keep a renewal from stalling.
Get the free carrier questionnaire →Severity
CVSS base score: 7.5 — HIGH
Weakness classification: CWE-416
Microsoft fix
- KB4537814 (Monthly Rollup)
- KB4537767 (IE Cumulative)
- KB4537762 (Security Update)
- KB4532691 (Security Update)
- KB4532693 (Security Update)
- KB4537789 (Security Update)
- KB4537776 (Security Update)
- KB4537764 (Security Update)
- KB4537820 (Monthly Rollup)
- KB4537821 (Monthly Rollup)
- KB4537810 (Monthly Rollup)
Microsoft Exploitability Index (assessed at update release): Exploitation Detected
Microsoft has confirmed in-the-wild exploitation in the latest software release. This aligns with CISA's listing of this CVE.
Vendor workaround
Vendor-published workaround
Impact of Workaround
Please note: Implementing these steps might result in reduced functionality for components or features that rely on jscript.dll. For example, depending on the environment, this could include client configurations that leverage proxy automatic configuration scripts (PAC scripts). These features and others may be impacted.
Microsoft recommends these mitigation steps only if there is indication that you are under elevated risk. If you implement the workaround, you will need to revert the mitigation steps before installing any future updates to continue to be protected.
By default, IE11, IE10, and IE9 uses Jscript9.dll which is not impacted by this vulnerability. This vulnerability only affects certain websites that utilize jscript as the scripting engine.
Restrict access to JScript.dll
For 32-bit systems, enter the following command at an administrative command prompt:
takeown /f %windir%\system32\jscript.dll
cacls %windir%\system32\jscript.dll /E /P everyone:N
For 64-bit systems, enter the following command at an administrative command prompt:
takeown /f %windir%\syswow64\jscript.dll
cacls %windir%\syswow64\jscript.dll /E /P everyone:N
takeown /f %windir%\system32\jscript.dll
cacls %windir%\system32\jscript.dll /E /P everyone:N
How to undo the workaround
For 32-bit systems, enter the following command at an administrative command prompt:
cacls %windir%\system32\jscript.dll /E /R everyone
For 64-bit systems, enter the following command at an administrative command prompt:
cacls %windir%\system32\jscript.dll /E /R everyone
cacls %windir%\syswow64\jscript.dll /E /R everyone
Vendor-published mitigation
By default, Internet Explorer on Windows Server 2008, Windows Server 2008 R2, Windows Server 2012, Windows Server 2012 R2, Windows Server 2016 and Windows Server 2019 runs in a restricted mode that is known as Enhanced Security Configuration. Enhanced Security Configuration is a group of preconfigured settings in Internet Explorer that can reduce the likelihood of a user or administrator downloading and running specially crafted web content on a server. This is a mitigating factor for websites that you have not added to the Internet Explorer Trusted sites zone.
A workaround reduces exposure while you patch — it is not a substitute for the update. Install the fix above as soon as you can.
CISA due date
Federal deadline: May 3, 2022. Federal agencies must complete the required action by this date. For private SMBs the deadline is advisory — but treat it as a strong recommendation, especially if you handle regulated data (HIPAA, GLBA, ABA model rules).
EPSS
EPSS score: 86.9% — higher than 100% of all scored CVEs.
EPSS estimates the probability of exploitation activity in the next 30 days. Every entry on this site is already confirmed exploited, so read it as relative urgency among the things you still have open, not as permission to wait.
Other exploited Microsoft Internet Explorer entries
More CISA KEV entries for Microsoft Internet Explorer. Same product line, same actively-exploited status.
Source
This entry comes from CISA's Known Exploited Vulnerabilities catalog, public US-Government data we pull daily. The plain-language framing and the what-to-do guidance above are ours. View the original entry on cisa.gov.