CVE-2026-72971: Microsoft Windows 11 version 26H1

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

CVSS 5.5 MediumEPSS 0.0036 · 30th percentile

Published by the CVE Program (CNA: microsoft) at 11 Aug 2026, 17:05 UTC. agentprime has not analysed this yet, so whether it affects any app is not known. This CVE names a vendor and product rather than a package, so the lockfile check doesn’t match it.

Affected products, as the CNA wrote them
Vendor	Product	Versions
Microsoft	Windows 11 version 26H1	affected 10.0.28000.0 to before 10.0.28000.2704 custom

Identifiers

CVE-2026-72971

CNA

microsoft

Weakness (CWE)

CWE-59

Machine-written summary

Summary written by Claude Haiku from the source advisory. Not reviewed by a person.

Microsoft Windows 11 version 26H1, from 10.0.28000.0 before 10.0.28000.2704, contains a link-following flaw in the Windows Container Isolation FS Filter Driver (unionfs.sys). An attacker with local, authorized access can exploit it to tamper with files. The source gives few details beyond this. Upgrade to 10.0.28000.2704 or later. No workaround is listed.

Written 12 Nov 2026.

Not analysed yet

We haven’t published our own analysis of this CVE. If a person reviews it, this page will say what’s affected and what has to be true for it to matter.

Severity and exploitation

Score	Rating	CVSS	Vector	Source
5.5	Medium	3.1	CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N/E:U/RL:O/RC:C	CNA (microsoft)

CISA KEV Not listed.
EPSS 0.0036, the 30th percentile, on 12 Nov 2026: FIRST’s estimate of the chance of exploitation in the next 30 days.

Timeline

11 Aug 2026, 17:05 UTC Confirmed by the CVE List

Sources

References from the CNA

msrc.microsoft.com/update-guide/vulnerability/CVE-2026-72971 vendor-advisorypatch

Facts on this page come from the CVE List as the CNA published them, with CVSS from the sources named above, CISA KEV and FIRST EPSS. Vendors, products and versions are shown as the CNA wrote them. We don’t reproduce the CVE’s description.