Microsoft Internet Explorer Scripting Engine Memory Corruption Vulnerability
CVE-2019-1367 is a security vulnerability in Microsoft Internet Explorer, added to CISA KEV on November 3, 2021. Patch order: first of four. Known ransomware use: yes.
What is CVE-2019-1367?
Microsoft Internet Explorer contains a memory corruption vulnerability in how the scripting engine handles objects in memory. Successful exploitation allows for remote code execution in the context of the current user.
Known to be used in ransomware campaigns. Active threat actors have chained this vulnerability into ransomware operations — treat patching as a same-week priority, not a "next maintenance window" task. The fix is the same one below; the urgency is higher.
VulnCheck tracked exploitation 772 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 is affected by CVE-2019-1367?
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 should I do about CVE-2019-1367?
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. Request a free review.
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-787
Microsoft fix
- KB4520007 (Monthly Rollup)
- KB4519974 (IE Cumulative)
- KB4520002 (Monthly Rollup)
- KB4520010 (Security Update)
- KB4520008 (Security Update)
- KB4519338 (Security Update)
- KB4520004 (Security Update)
- KB4517389 (Security Update)
- KB4520011 (Security Update)
- KB4519998 (Security Update)
- KB4519976 (Monthly Rollup)
- KB4520005 (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
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
Impact of Workaround
Implementing these steps might result in reduced functionality for components or features that rely on jscript.dll. To be fully protected, Microsoft recommends the update be installed as soon as possible. Please revert the mitigation steps before installing the update to return to a full state.
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.
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
CISA's listed due date: May 3, 2022.
Federal civilian agencies work under CISA's Binding Operational Directive 26-04, which replaced BOD 22-01 on June 10, 2026. It sets the deadline for each affected system by:
- How exposed that system is to the internet
- Whether the attack can be automated
- How much control it gives an attacker
Its table gives catalogued vulnerabilities 3 or 14 days.
None of this binds a private business, but treat the date as a strong recommendation, especially if you handle regulated data (HIPAA, GLBA, ABA model rules).
EPSS
EPSS score: 52.4% — higher than 99% 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.