CVE-2026-50305 Overview
CVE-2026-50305 is a use-after-free vulnerability in the Microsoft Brokering File System affecting Windows 11 and Windows Server 2025. An authorized local attacker can exploit the flaw to elevate privileges on the target system. The vulnerability is tracked under CWE-416 (Use After Free) and CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization).
Microsoft published the advisory on July 14, 2026. Successful exploitation grants attackers the ability to run code in a higher-privileged context, typically SYSTEM, from a low-privileged user account.
Critical Impact
A local authenticated attacker can achieve SYSTEM-level privileges on unpatched Windows 11 and Windows Server 2025 hosts, breaking the security boundary between standard users and the operating system.
Affected Products
- Microsoft Windows 11 24H2 (x64 and ARM64)
- Microsoft Windows 11 25H2 (x64 and ARM64)
- Microsoft Windows 11 26H1 (x64 and ARM64)
- Microsoft Windows Server 2025
Discovery Timeline
- 2026-07-14 - CVE-2026-50305 published to NVD and Microsoft advisory released
- 2026-07-16 - Last updated in NVD database
Technical Details for CVE-2026-50305
Vulnerability Analysis
The Microsoft Brokering File System (BFS) mediates access to file resources for sandboxed and brokered processes on Windows. A use-after-free condition in this component allows an attacker to reference memory that has already been released. When the freed memory is reallocated with attacker-controlled data, the subsequent dereference redirects execution or corrupts kernel state.
The CWE-362 classification indicates that concurrent execution paths race to access shared BFS objects without proper synchronization. One thread frees the object while another retains a stale pointer. This overlap between free and reuse produces the exploitable window.
Exploitation requires local access and low-privileged authenticated execution. No user interaction is needed, and the attack complexity is low, making the flaw practical for post-compromise privilege escalation chains.
Root Cause
The root cause is improper lifetime management of kernel objects handled by the Brokering File System. A race condition allows one thread to release an object while another thread continues to operate on the same pointer. The dangling reference is then dereferenced, producing a CWE-416 use-after-free condition in kernel context.
Attack Vector
The attack vector is local. An attacker who has already obtained code execution as a standard user triggers the race by invoking BFS operations concurrently. By spraying the kernel pool to reoccupy the freed allocation, the attacker gains control over object fields such as function pointers or handle tables. Dereferencing the corrupted object yields arbitrary read, write, or execution in kernel mode, which is used to elevate the calling process token to SYSTEM.
No public proof-of-concept exploit or CISA KEV listing exists for CVE-2026-50305 at the time of publication. The EPSS score is 0.184%, reflecting a low current probability of exploitation observed in the wild.
Detection Methods for CVE-2026-50305
Indicators of Compromise
- Unexpected process token elevation where a child process obtains SYSTEM privileges from a standard-user parent
- Kernel bugchecks or Event ID 41 crashes referencing the Brokering File System driver on affected Windows builds
- Anomalous handle duplication or process creation originating from sandboxed or low-integrity processes
Detection Strategies
- Monitor for local privilege escalation patterns: standard-user processes spawning cmd.exe, powershell.exe, or rundll32.exe with SYSTEM integrity levels
- Correlate Windows Security Event ID 4688 (process creation) with sudden integrity level changes on the same session
- Baseline BFS driver interactions and flag high-frequency, concurrent I/O request patterns from unprivileged processes
Monitoring Recommendations
- Enable kernel-mode auditing and forward crash dumps referencing BFS components to a central analysis pipeline
- Track patch compliance for the July 2026 Microsoft security update across all Windows 11 and Windows Server 2025 endpoints
- Alert on unsigned or unusual drivers loading in proximity to BFS activity, which may indicate exploitation tooling
How to Mitigate CVE-2026-50305
Immediate Actions Required
- Apply the Microsoft security update referenced in the Microsoft CVE-2026-50305 Advisory to all affected systems
- Prioritize patching multi-user systems, terminal servers, and shared workstations where local privilege escalation carries the highest impact
- Audit local account membership and remove unnecessary interactive logon rights from non-administrative users
Patch Information
Microsoft has released a security update addressing CVE-2026-50305. Refer to the Microsoft CVE-2026-50305 Advisory for the exact KB number applicable to each Windows 11 build and Windows Server 2025 installation.
Workarounds
- No official workaround has been published by Microsoft. Applying the security update is the required remediation.
- Reduce exposure by restricting local logon rights and enforcing least-privilege policies until patching completes
- Enable attack surface reduction rules and application control policies to limit execution of untrusted binaries that could deliver the exploit
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
