Microsoft Malware Protection Engine Improper Restriction of Operations Vulnerability
CVE-2017-8540 is a security vulnerability in Microsoft Malware Protection Engine, added to CISA KEV on March 3, 2022. Patch priority: Plan to patch.
What it is
The Microsoft Malware Protection Engine running on Microsoft Forefront and Microsoft Defender on Microsoft Windows Server 2008 SP2 and R2 SP1, Windows 7 SP1, Windows 8.1, Windows Server 2012 Gold and R2, Windows RT 8.1, Windows 10 Gold, 1511, 1607, and 1703, and Windows Server 2016, Microsoft Exchange Server 2013 and 2016, does not properly scan a specially crafted file leading to memory corruption. aka "Microsoft Malware Protection Engine Remote Code Execution Vulnerability".
Who's affected
Affects anyone running Microsoft Malware Protection Engine. 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: 7.8 — HIGH
Weakness classification: CWE-787
Microsoft fix
No fixing KB is published yet in the Microsoft Security Update Guide for this CVE. Check Microsoft's advisory page directly if you need to verify whether an update has shipped.
Microsoft Exploitability Index (assessed at update release): Exploitation Less Likely
This CVE is on CISA's Known Exploited Vulnerabilities catalog. Microsoft's index reflects their release-time forecast, not current observed activity, and is not automatically revised upward when exploitation appears later.
Vendor workaround
Vendor-published mitigation
The following mitigating factors may be helpful in your situation: Systems running supported versions of Windows Server 2008 R2 are not affected if the Desktop Experience feature is not installed.
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: March 24, 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: 72.0% — 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.
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.