How to check if you are exposed to CVE-2026-41091
- Find every Microsoft Defender system you or your clients run, including ones exposed to the internet. Those come first: CISA only lists flaws attackers are already using.
- Compare each version with the fixed versions in the vendor advisory below. Where no fix exists yet, apply the vendor’s mitigation or take the system off the internet.
- Run a credentialed vulnerability scan to catch the systems you missed, then check that the next scan no longer reports CVE-2026-41091.
US federal agencies had to fix this by 2026-06-03. Everyone else should treat that deadline as a guide: if it has passed, this is overdue.
Affected versions
Versions the National Vulnerability Database lists as vulnerable to CVE-2026-41091. Check the vendor advisory for the exact fixed builds before you sign anything off.
| Product | Vulnerable versions |
|---|---|
| Microsoft Malware Protection Engine | from 1.1.26030.3008 before 1.1.26040.8 |
Timeline
- · Published in the National Vulnerability Database
- · Added to CISA's Known Exploited Vulnerabilities catalog, the same day it was published
- · Fix-by date for US federal agencies, passed 151 days ago
Vendor advisories and fixes
Weakness type
More exploited Microsoft vulnerabilities
CISA lists 390 exploited Microsoft vulnerabilities. The closest matches:
- CVE-2026-45498Microsoft Defender Denial of Service VulnerabilityAdded 2026-05-20
- CVE-2026-33825Microsoft Defender Insufficient Granularity of Access Control VulnerabilityAdded 2026-04-22
- CVE-2022-44698Microsoft Defender SmartScreen Security Feature Bypass VulnerabilityAdded 2022-12-13
- CVE-2021-1647Microsoft Defender Remote Code Execution VulnerabilityAdded 2021-11-03
- CVE-2026-96951Microsoft Windows Command Injection VulnerabilityAdded 2026-10-13
- CVE-2026-65660Microsoft SharePoint Code Injection VulnerabilityAdded 2026-09-25
- CVE-2026-85880Microsoft Windows Heap-Based Buffer Overflow VulnerabilityAdded 2026-09-08
- CVE-2026-81963Microsoft Windows Link Following VulnerabilityAdded 2026-09-08
Keep going
Sources: CISA Known Exploited Vulnerabilities catalog (version 2026.10.30); EPSS data from FIRST.org; CVSS and descriptions from the NIST National Vulnerability Database. Checked 2026-11-01. This product uses the NVD API but is not endorsed or certified by the NVD.