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Windows Container Isolation CVE-2026-72971

| EUVDEUVD-2026-56603 MEDIUM
Improper Link Resolution Before File Access (CWE-59)
2026-08-11 secure@microsoft.com GHSA-mq4h-r45f-27gp
5.5
CVSS 3.1 · Vendor: microsoft
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Severity by source

Vendor (microsoft) PRIMARY
5.5 MEDIUM
AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
vuln.today AI
5.5 MEDIUM

Local-only attack requiring a low-privilege session to plant symlinks; no confidentiality loss, no scope change, pure integrity impact on the vulnerable system.

3.1 AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
4.0 AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:H/VA:N/SC:N/SI:N/SA:N

Primary rating from Vendor (microsoft).

CVSS VectorVendor: microsoft

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N
Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
High
Availability
None

Lifecycle Timeline

3
Analysis Generated
Aug 11, 2026 - 22:02 vuln.today
Patch available
Aug 11, 2026 - 18:19 EUVD
CVE Published
Aug 11, 2026 - 17:19 cve.org
MEDIUM 5.5

DescriptionCVE.org

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.

AnalysisAI

Symlink-following in the Windows Container Isolation FS Filter Driver (unionfs.sys) enables a locally authenticated attacker with low privileges to tamper with files outside the expected isolation boundary. Affected systems run Windows 11 version 26H1 builds prior to 10.0.28000.2704. …

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Attack ChainAIDerived

Hypothetical attack flow derived from CVE metadata

Access
Gain low-privilege local session
Delivery
Identify file target outside container boundary
Exploit
Plant crafted symbolic link in driver-accessible path
Execution
Trigger file operation through unionfs.sys
Persist
Driver follows link without validation
Impact
Overwrite or corrupt target file

Vulnerability AssessmentAI

Exploitation Exploitation requires a locally authenticated session with at least low-privilege (standard user) rights on the target Windows 11 26H1 system. … Additional conditions and limiting factors are described in the full assessment.
Risk Assessment The CVSS 3.1 base score of 5.5 (AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:H/A:N) accurately reflects a moderate local tampering risk: attack complexity is low, but exploitation is confined to the local machine and requires at least a low-privilege authenticated session. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in.
Exploit Scenario A locally authenticated low-privilege user on a Windows 11 26H1 system plants a symbolic link in a location that the Container Isolation FS Filter Driver (unionfs.sys) will traverse during a file operation. When the driver processes the link without resolving it to its true target, the attacker's crafted path redirects the write or modify operation to an arbitrary file on the host filesystem, allowing them to corrupt or overwrite files they would not ordinarily have write access to. …
Remediation Apply the vendor-released patch that brings Windows 11 26H1 to build 10.0.28000.2704 or later via Windows Update or WSUS; this is the only confirmed fix per EUVD-2026-56603 and the Microsoft Security Response Center advisory at https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-72971. … Detailed patch versions, workarounds, and compensating controls in full report.

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CVE-2026-72971 vulnerability details – vuln.today

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