Windows Brokering File System: Privilege escalation via incorrect permissions
Summary
The Windows Brokering File System (bfs.sys), a component of Windows 11 and Windows Server 2025, contains an incorrect permission assignment for a critical resource. An authorized local attacker with low privileges can elevate privileges to a higher level, potentially up to SYSTEM. The attack requires local access and an existing user account, so the flaw is not remotely exploitable.
Affected
- Windows 11 Version 24H2: 10.0.26100.0 to before 10.0.26100.9974
- Windows 11 Version 25H2: 10.0.26200.0 to before 10.0.26200.9974
- Windows 11 Version 26H1: 10.0.28000.0 to before 10.0.28000.3501
- Windows 11 Version 26H2: 10.0.26300.0 to before 10.0.26300.9974 (build number from third-party source, to be verified on MSRC)
- Windows Server 2025 (including Server Core): 10.0.26100.0 to before 10.0.26100.33822 (to be verified on MSRC)
Fixed in
- Windows 11 24H2: 10.0.26100.9974 or later
- Windows 11 25H2: 10.0.26200.9974 or later
- Windows 11 26H1: 10.0.28000.3501 or later
- Windows 11 26H2: 10.0.26300.9974 or later (to be verified on MSRC)
- Windows Server 2025: 10.0.26100.33822 or later (to be verified on MSRC)
- Update KB numbers: Unknown.
Workaround
Unknown. No Microsoft or third-party workaround has been identified. Patching is the remedy.
Exploitation
- The CVSS exploit maturity is E:U (unproven), meaning no exploit code was known at publication.
- CISA SSVC: exploitation none, not automatable.
- No evidence of exploitation in the wild was found. The CISA KEV catalogue was not checked directly.
Our recommendation
- Install the November 2026 cumulative update on all affected Windows 11 and Windows Server 2025 systems.
- Verify the installed build numbers against the MSRC advisory.
- Prioritise workstations and shared systems where users can run untrusted software and servers with interactive logons.
- Review local accounts and monitor for unexpected privilege changes or SYSTEM processes spawned by low-privilege users.
Information from Microsoft (Patch Tuesday November 2026)
Public exploits
PoC-in-GitHub, Metasploit and Exploit-DB list nothing for this CVE.
Research sources
- Microsoft Security Update Guide: CVE-2026-85929 msrc.microsoft.com
- CVE.org record CVE-2026-85929 www.cve.org
- Strix AI: CVE-2026-85929 (version data, third-party) www.strix.ai
- Cybersecurity News: Windows Brokering File System vulnerability cybersecuritynews.com
Researched and written up in English and German by an AI (Claude by Anthropic) based on NVD, CISA, EPSS and the sources listed. The vendor information is authoritative. Researched on 11 Nov 2026, 03:21.
Original description (NVD)
Incorrect permission assignment for critical resource in Windows Brokering File System allows an authorized attacker to elevate privileges locally.
NVD references (1)
Sources
The tracker combines official, freely usable data sources – updated continuously:
- NVD (NIST) – CVEs, rating (CVSS), affected products
- CISA KEV – vulnerabilities confirmed by CISA as actively exploited
- CISA Vulnrichment – CISA assessment (SSVC) in the official CVE record
- FIRST EPSS – probability of exploitation
- Microsoft MSRC – Patch Tuesday: vulnerabilities, severity, updates
- PoC-in-GitHub – public proof-of-concept repositories
- Metasploit (Rapid7) – modules of the Metasploit Framework
- Exploit-DB (OffSec) – archive of public exploits (links only)
- Patch days: official vendor pages (linked per vendor) (Vendor patch days)
This product uses data from the NVD API but is not endorsed or certified by the NVD. EPSS data © FIRST.org.
Affected? We can help.
We check whether your systems are affected, install updates and close the gap – continuously with the System Health Checker if you wish.