CVE-2026-72971: Windows Container Isolation FS Filter Driver (unionfs.sys) Tampering Vulnerability

Severity: medium (CVSS 5.5 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.4% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-08-11 · updated 2026-10-30
Weakness: CWE-59

Description

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.

Affected products

Microsoft Windows 11 version 26H1: before 10.0.28000.2704 — fixed in 10.0.28000.2704
Microsoft Windows 11 version 26H1: from 10.0.28000.0 before 10.0.28000.2704 — fixed in 10.0.28000.2704

How to fix

Upgrade to a fixed version: Microsoft Windows 11 version 26H1 10.0.28000.2704; Microsoft Windows 11 version 26H1 10.0.28000.2704. Check the vendor advisory for mitigations.

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-72971

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