CVE-2026-72971

Windows Container Isolation FS Filter Driver (unionfs.sys) Tampering Vulnerability

CVE-2026-72971 is fixed in 2 products on 1 platform, first by KB5121000, released August 11, 2026. It is not reported as exploited. Patch Radar priority: Routine.

RoutinePublicly disclosed

CVSS

5.5

Important

Exploitation

None reported

Exploitation Unlikely

CISA KEV

Not listed

Not in the Known Exploited Vulnerabilities catalog

EPSS

0.0036

30th percentile

<p>Improper link resolution before file access ('link following') in Windows Container Isolation FS Filter Driver (unionfs.sys) allows an authorized attacker to perform tampering locally.</p>

Where it's fixed

Product	Fixed in	Fix	Released
Microsoft
Windows 11 Version 26H1 for ARM64-based Systems	28000.2704	KB5121000	Aug 11, 2026
Windows 11 version 26H1 for x64-based Systems	28000.2704	KB5121000	Aug 11, 2026

Details

Published
August 11, 2026
Weakness
Improper Link Resolution Before File Access ('Link Following')
Vendor advisory
https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-72971

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