CVE-2025-53137 Overview
CVE-2025-53137 is a use-after-free vulnerability [CWE-416] in the Windows Ancillary Function Driver for WinSock (afd.sys). An authenticated local attacker can trigger the flaw to elevate privileges from a low-integrity user context to SYSTEM. Microsoft addressed the issue in the August 2025 security update cycle. The vulnerability affects a broad range of supported Windows client and server releases, including Windows 10, Windows 11, and Windows Server 2008 through Windows Server 2025.
Critical Impact
Successful exploitation grants SYSTEM-level privileges on the host, enabling full compromise of the local operating system and downstream lateral movement.
Affected Products
- Microsoft Windows 10 (1507, 1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (22H2, 23H2, 24H2)
- Microsoft Windows Server 2008, 2012, 2016, 2019, 2022, 2022 23H2, and 2025
Discovery Timeline
- 2025-08-12 - CVE-2025-53137 published to NVD alongside the Microsoft Security Update CVE-2025-53137
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-53137
Vulnerability Analysis
The Ancillary Function Driver for WinSock (afd.sys) is the kernel-mode driver that services user-mode WinSock calls through IOCTLs. A use-after-free condition in this driver allows an attacker with local, authenticated access to reuse a freed kernel object before the driver clears its references. Because afd.sys runs in kernel context, controlled reuse of the freed allocation yields arbitrary kernel read/write primitives and, ultimately, code execution at SYSTEM.
The attack requires local access and low privileges, and Microsoft classifies exploitation as high complexity due to the timing conditions needed to reclaim the freed object. Exploitation does not require user interaction.
Root Cause
The root cause is improper object lifetime management inside afd.sys [CWE-416]. A code path releases a kernel object while another path retains a dangling pointer to the same allocation. When the retained pointer is later dereferenced, the driver operates on attacker-influenced memory that has been reclaimed by a subsequent allocation.
Attack Vector
An authenticated local user issues a specific sequence of WinSock IOCTLs to afd.sys to reach the vulnerable code path. The attacker races the free with a controlled kernel allocation to place attacker-shaped data at the reclaimed address. Dereferencing the dangling pointer then produces a kernel primitive that is escalated to SYSTEM through standard kernel exploitation techniques such as token replacement.
No public proof-of-concept or in-the-wild exploitation has been reported at the time of writing. Refer to the Microsoft Security Update CVE-2025-53137 for vendor-supplied technical context.
Detection Methods for CVE-2025-53137
Indicators of Compromise
- Unexpected child processes spawned by services or user processes running as NT AUTHORITY\SYSTEM shortly after a low-privileged process interacted with WinSock APIs.
- Kernel crash dumps referencing afd.sys with bug checks consistent with pool corruption or invalid pointer dereferences (for example BAD_POOL_CALLER, KERNEL_MODE_HEAP_CORRUPTION).
- Presence of known local privilege escalation tooling on endpoints, particularly tools that target AFD IOCTL surfaces.
Detection Strategies
- Monitor for token manipulation patterns such as a process handle opening System (PID 4) followed by a privilege change on the caller.
- Alert on abnormal use of NtDeviceIoControlFile against \Device\Afd from non-system, low-integrity processes with atypical IOCTL codes.
- Correlate local logon events (Event ID 4624 type 2/3) with subsequent SYSTEM-level process creation from the same user session.
Monitoring Recommendations
- Enable kernel-mode telemetry and Windows Defender ASR-style rules that capture driver-level anomalies and integrity-level transitions.
- Ship Sysmon Event ID 1 (process create) and Event ID 10 (process access) with command-line and parent-child context to a SIEM for detection engineering.
- Track patch compliance on all Windows 10, Windows 11, and Windows Server assets against the August 2025 cumulative updates.
How to Mitigate CVE-2025-53137
Immediate Actions Required
- Deploy the August 2025 Microsoft security updates that address CVE-2025-53137 across all supported Windows client and server SKUs listed in the advisory.
- Prioritize patching multi-user systems such as Remote Desktop Session Hosts, jump servers, and developer workstations where local privilege escalation has the highest blast radius.
- Audit local account inventories and remove unnecessary interactive logon rights, since exploitation requires an authenticated local session.
Patch Information
Microsoft published fixed builds for each affected Windows release via the August 2025 Patch Tuesday. Consult the Microsoft Security Update CVE-2025-53137 advisory for the specific KB article and minimum build number for each operating system version, and apply the corresponding cumulative update through Windows Update, WSUS, or your patch management platform.
Workarounds
- No vendor-supplied workaround replaces the patch; apply the update as the primary mitigation.
- Restrict local logon rights and enforce least privilege to reduce the population of users able to reach the vulnerable IOCTL surface.
- Enable attack surface reduction, credential guard, and HVCI where supported to raise the cost of kernel exploitation on unpatched hosts.
# Verify installed updates on a Windows host (run from an elevated PowerShell prompt)
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 20
# Confirm afd.sys file version after patching
(Get-Item C:\Windows\System32\drivers\afd.sys).VersionInfo
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
