CVE-2025-49693 — Microsoft Brokering File System Elevation of Privilege Vulnerability

Executive Summary

Double free in Microsoft Brokering File System allows an authorized attacker to elevate privileges locally.

Overview

7.8

CVSS HIGH

Important

MS Severity

Not Exploited

MS Exploit Status

Less Likely

MS Exploit Likelihood

Category Elevation of Privilege

Weakness CWE-415: Double Free

Released Jul 8 2025

Last Updated Jul 8 2025

Publicly Disclosed No

CISA KEV Not Listed

Known Exploits None Known

EPSS Score 0.00374 — 0.30408 percentile

NVD CVSS 7.8 HIGH — matches MSRC

CVSS Vector

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C

ATTACK VECTOR

Local

ATTACK COMPLEXITY

Low

PRIVILEGES REQUIRED

Low

USER INTERACTION

None

SCOPE

Unchanged

CONFIDENTIALITY

High

INTEGRITY

High

AVAILABILITY

High

EXPLOIT CODE MATURITY

Unproven

REMEDIATION LEVEL

Official Fix

REPORT CONFIDENCE

Confirmed

Temporal Score: 6.8

EPSS Score

0.00374

probability of exploitation in the next 30 days

0.30408 percentile - updated 2026-08-14

View on FIRST.org

Affected Products

9 affected products

Product	KB Article	Severity	Impact	Restart Required
Windows 11 Version 22H2 for ARM64-based Systems	`5062552 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 22H2 for x64-based Systems	`5062552 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 23H2 for ARM64-based Systems	`5062552 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 23H2 for x64-based Systems	`5062552 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 24H2 for ARM64-based Systems	`5062553 (Security Update)`	Important	Elevation of Privilege	Yes
Windows 11 Version 24H2 for x64-based Systems	`5062553 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2022, 23H2 Edition (Server Core installation)	`5062570 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2025	`5062553 (Security Update)`	Important	Elevation of Privilege	Yes
Windows Server 2025 (Server Core installation)	`5062553 (Security Update)`	Important	Elevation of Privilege	Yes

Patches

3 patches

Article	Type	Restart
`5062552`	Security Update	Yes
`5062553`	Security Update	Yes
`5062570`	Security Update	Yes

Patch Diff

ghidriff · bfs.sys (KB5062553)

Double free (CWE-415) in the Microsoft Brokering File System driver bfs.sys BfsInsertPolicyEntry failure path, local EoP to SYSTEM (race, AC:H). Reached via \Device\Bfs IOCTL 0x228004 (BfsDeviceIoControl -> BfsProcessSetPolicyRequest). Handling a SetPolicy insert, BfsInsertPolicyEntry ExAllocatePool2's a policy entry (tag EsfB) plus pUserId and pContainerId (tag SsfB), assigns pUserId/pContainerId to NewPolicyEntry (ownership transfer), ref-counts (RefNo=2 after two InterlockedIncrements), inserts into the policy hash table, then provisions storage (BfsOpenPolicyDirectory/BfsCreateStorage). On failure it calls BfsDereferencePolicyEntryEx twice; the second drops RefNo to 0 and frees PolicyEntry->pUserId, ->pContainerId and the entry. The failure path THEN also ExFreePoolWithTag(pUserId)/ExFreePoolWithTag(pContainerId) on the same freed buffers -> double free / pool corruption. Diff of bfs.sys 10.0.26100.4484 -> .4652 (Jul 8 2025, KB5062553) confirms the fix: gated behind CFR flag Feature_3148938554, BfsInsertPolicyEntry nulls the local pUserId/pContainerId pointers immediately after ownership is transferred to the policy entry, so the failure-path ExFreePoolWithTag(pUserId/pContainerId) sees NULL and skips the second free. The BFS interface requires an AppSilo token (BfsIsApplicableToken / SeAppSiloSid), reached via AppContainer/AppSilo. Note: our diff shows Feature_3148938554 (build/arch); paired UAF is CVE-2025-49677.

Pre-patch version 10.0.26100.4484 Download

Post-patch version 10.0.26100.4652 Download

Function	Address	Change	Note
`BfsInsertPolicyEntry`	`code change`	code (null local pUserId/pContainerId after ownership transfer, CFR-gated)	Pre: on BfsOpenPolicyDirectory/BfsCreateStorage failure, BfsDereferencePolicyEntryEx (RefNo->0) frees PolicyEntry->pUserId/->pContainerId, then the path also ExFreePoolWithTag(pUserId)/ExFreePoolWithTag(pContainerId) -> double free. Post (Feature_3148938554): sets local pUserId=0/pContainerId=0 right after NewPolicyEntry->pUserId/->pContainerId assignment, so the later frees are skipped.
`Feature_3148938554`	`gate`	added (CFR gate)	CFR flag gating the null-after-transfer double-free fix (and the paired policy-entry lifecycle rework); original path still ships when disabled.

View full diff report View RCA report

Attack Path

A failed BfsCreateStorage frees pUserId/pContainerId via the policy entry, then the failure path frees them again

Derived from the patch delta: the checks added by the vendor identify which fields crossed a trust boundary unvalidated. Reachability and privilege are taken from the call chain in the RCA report.

Known Exploits

No known exploits have been linked for this CVE yet. When available, exploit references will be sourced from public repositories and may be unverified, incomplete, or non-functional. Always review code carefully before use in any environment.

Acknowledgments

ChenJian with Sea Security Orca Team

References

MSRC Advisory MITRE NVD