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Microsoft fixes two zero day Defender bugs under active attack
Microsoft has released patches for two critical vulnerabilities in its Defender software, labeled CVE-2026-41091 and CVE-2026-45498, which have been exploited in the wild as zero-days. CVE-2026-41091, rated at 7.8 on the CVSS scale, allows local privilege escalation due to improper link resolution, while CVE-2026-45498 is a denial-of-service flaw rated at 4.0. These vulnerabilities have been added to CISA's Known Exploited Vulnerabilities list, with a recommendation for federal agencies to apply patches by June 3.
Additionally, CISA confirmed in-the-wild exploitation of older vulnerabilities dating back several years, emphasizing the importance of reviewing and addressing these security issues quickly.
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Story timeline CVE-2026-41091
Full timelineShow as table
| Published (UTC) | Outlet | Headline |
|---|---|---|
| Wed 20 May · 18:02 UTC | CISA | CISA adds seven KEV flaws, including 2026 Microsoft Defender bugs |
| Wed 20 May · 19:45 UTC | CISA | CISA warns of active exploit in Microsoft Defender CVE-2026-41091 |
| Wed 20 May · 20:13 UTC | CISA | CISA warns of active exploit in Microsoft Defender CVE-2026-41091 |
| Thu 21 May · 10:21 UTC | SecurityWeek | Microsoft fixes two zero day Defender bugs under active attack (this article) |
| Thu 21 May · 18:41 UTC | Malwarebytes | Microsoft Defender vulnerabilities are being exploited in the wild |
| Thu 21 May · 21:32 UTC | Security Affairs | CISA Adds Critical Flaws in Windows, Office, Defender to KEV List |
| Tue 9 Jun · 23:49 UTC | Security Affairs | Microsoft patches CVE-2026-41091 amid record 208 CVE update |