KB5121000: CVEs fixed (Windows update (KB))

KB5121000 fixes 3 tracked CVEs. Affected systems and fixed versions.

• CVE-2026-62772 HIGH 7.8 UPGRADE Heap-based buffer overflow in Windows Container Isolation FS Filter Driver (unionfs.sys) allows an authorized
• CVE-2026-62799 HIGH 7.8 UPGRADE Heap-based buffer overflow in Windows SMB Client allows an authorized attacker to elevate privileges locally.
• CVE-2026-72971 MEDIUM 5.5 UPGRADE Improper link resolution before file access ('link following') in Windows Container Isolation FS Filter Driver

Applies to

• Windows 11 Version 26H1 for ARM64-based Systems · fixed in 10.0.28000.2704
• Windows 11 version 26H1 for x64-based Systems · fixed in 10.0.28000.2704

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