Microsoft Windows 11 26H1 Container Isolation FS Filter Driver unionfs.sys buffer overflow

Summaryinfo

A vulnerability was found in Microsoft Windows 11 26H1. It has been declared as very critical. This affects an unknown part of the file unionfs.sys of the component Container Isolation FS Filter Driver. Such manipulation leads to buffer overflow. This vulnerability is listed as CVE-2026-62772. The attack must be carried out locally. There is no available exploit.

Detailsinfo

A vulnerability, which was classified as very critical, has been found in Microsoft Windows 11 26H1. Affected by this issue is some unknown processing of the file unionfs.sys of the component Container Isolation FS Filter Driver. The manipulation with an unknown input leads to a buffer overflow vulnerability. Using CWE to declare the problem leads to CWE-120. The product copies an input buffer to an output buffer without verifying that the size of the input buffer is less than the size of the output buffer, leading to a buffer overflow. Impacted is confidentiality, integrity, and availability. CVE summarizes:

Heap-based buffer overflow in Windows Container Isolation FS Filter Driver (unionfs.sys) allows an authorized attacker to elevate privileges locally.

The advisory is available at msrc.microsoft.com. This vulnerability is handled as CVE-2026-62772 since 07/14/2026. The exploitation is known to be easy. Local access is required to approach this attack. Technical details are known, but there is no available exploit. The structure of the vulnerability defines a possible price range of USD $5k-$25k at the moment (estimation calculated on 08/11/2026).

Upgrading to version 10.0.28000.2704 eliminates this vulnerability.

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Productinfo

Type

• Operating System

Vendor

• Microsoft

Name

• Windows

Version

• 11 26H1

License

• commercial

Website

• Vendor: https://www.microsoft.com/
• Product: https://www.microsoft.com/en-us/windows

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