CVE-2025-53134 Overview
CVE-2025-53134 is a race condition vulnerability in the Windows Ancillary Function Driver for WinSock (afd.sys). The flaw stems from concurrent execution using a shared resource with improper synchronization. An authorized local attacker can exploit this weakness to elevate privileges on affected Windows systems. Microsoft rated the issue HIGH severity with a CVSS 3.1 base score of 7.0. The vulnerability affects a broad range of Windows client and server versions, from Windows 10 1507 through Windows 11 24H2 and Windows Server 2008 through Windows Server 2025. The EPSS score is 0.313%, placing it in the 24th percentile for likelihood of exploitation.
Critical Impact
A successful exploit allows a low-privileged local user to gain SYSTEM-level privileges by winning a kernel-mode race condition in afd.sys.
Affected Products
- Microsoft Windows 10 (1507, 1607, 1809, 21H2, 22H2) and Windows 11 (22H2, 23H2, 24H2)
- Microsoft Windows Server 2008, 2012, 2016, 2019, 2022, 2022 23H2, and 2025
- Windows Ancillary Function Driver for WinSock (afd.sys) kernel component
Discovery Timeline
- 2025-08-12 - CVE-2025-53134 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-53134
Vulnerability Analysis
The Windows Ancillary Function Driver for WinSock (afd.sys) is a kernel-mode driver that provides the interface between user-mode WinSock calls and the underlying Transport Driver Interface (TDI). It handles socket operations invoked from user space via DeviceIoControl requests. The driver manages shared socket state structures accessed by multiple concurrent threads.
The flaw is a race condition [CWE-362] involving concurrent execution using a shared resource with improper synchronization. When multiple threads issue overlapping I/O control requests targeting the same socket object, the driver fails to enforce proper locking on a shared structure. An attacker who wins this race can manipulate kernel memory in a way that grants elevated privileges.
Exploitation requires local access and low privileges. The high attack complexity reflects the timing precision needed to consistently win the race window.
Root Cause
The root cause is missing or insufficient synchronization on a shared kernel object accessed by concurrent WinSock operations. Two or more threads can reach a critical section simultaneously and mutate shared state without atomic guarantees. This produces an inconsistent object state that the attacker can weaponize for privilege escalation.
Attack Vector
The attack requires local code execution as an authenticated user. The adversary spawns multiple threads that repeatedly invoke targeted socket I/O control operations against the same AFD handle. By carefully aligning thread scheduling on multi-core systems, the attacker forces a TOCTOU condition inside afd.sys and corrupts kernel state to obtain SYSTEM privileges. See the Microsoft Security Update for CVE-2025-53134 for vendor technical details.
Detection Methods for CVE-2025-53134
Indicators of Compromise
- Unexpected process token elevation, especially processes spawned by standard user accounts suddenly running as NT AUTHORITY\SYSTEM.
- Repeated NtDeviceIoControlFile calls targeting \Device\Afd handles from a single non-privileged process within a short time window.
- Bugcheck events referencing afd.sys on systems that were previously stable.
Detection Strategies
- Monitor Sysmon Event ID 1 for child processes whose integrity level or user SID does not match the parent, indicating token theft or privilege elevation.
- Baseline normal AFD I/O patterns and alert on non-browser, non-service processes issuing high-volume overlapping WinSock IOCTLs.
- Correlate kernel crash telemetry from Windows Error Reporting with local logon activity to surface failed exploitation attempts.
Monitoring Recommendations
- Enable kernel-mode auditing and forward EDR telemetry for afd.sys interactions to a centralized data lake for retrospective hunting.
- Track patch deployment status for the August 2025 Microsoft security updates across all Windows endpoints and servers.
- Alert on new local administrator or SYSTEM-context processes launched shortly after suspicious multi-threaded socket activity.
How to Mitigate CVE-2025-53134
Immediate Actions Required
- Apply the August 2025 Microsoft security updates addressing CVE-2025-53134 to all affected Windows client and server versions.
- Prioritize patching of multi-user systems, terminal servers, and jump hosts where local low-privileged access is common.
- Audit local user accounts and remove unnecessary interactive logon rights to reduce the attack surface.
Patch Information
Microsoft released a security update on August 12, 2025 that resolves the improper synchronization in afd.sys. Refer to the Microsoft Security Update Guide for CVE-2025-53134 for the specific KB article and package for each affected Windows build.
Workarounds
- No official vendor workaround exists; patching is the only supported remediation.
- Restrict local logon and Remote Desktop access to trusted administrative accounts until patches are applied.
- Deploy application control policies such as Windows Defender Application Control (WDAC) to block execution of unsigned or unknown binaries that could deliver an exploit.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
