CVE-2025-53141 Overview
CVE-2025-53141 is a null pointer dereference vulnerability [CWE-476] in the Windows Ancillary Function Driver for WinSock (afd.sys). The flaw allows an authenticated local attacker to elevate privileges on affected Windows client and server operating systems. Microsoft addressed the issue as part of its security update cycle, with details published to the National Vulnerability Database (NVD) on August 12, 2025.
Because afd.sys runs in kernel mode, successful exploitation can yield SYSTEM-level code execution from a low-privileged user context. The vulnerability requires local access and low privileges but no user interaction.
Critical Impact
Authenticated local attackers can elevate to SYSTEM by triggering a null pointer dereference in the kernel-mode afd.sys driver, resulting in a full compromise of confidentiality, integrity, and availability on the affected host.
Affected Products
- Microsoft Windows 10 (1507, 1607, 1809, 21H2, 22H2) and Windows 11 (22H2, 23H2, 24H2)
- Microsoft Windows Server 2008, 2012, 2016, 2019, 2022 (including 23H2), and 2025
- All supported x86 and x64 builds shipping the Ancillary Function Driver for WinSock (afd.sys)
Discovery Timeline
- 2025-08-12 - CVE-2025-53141 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-53141
Vulnerability Analysis
The vulnerability resides in the Ancillary Function Driver for WinSock (afd.sys), the kernel component that services WinSock user-mode requests via I/O control codes (IOCTLs). A code path in the driver dereferences a pointer without first validating that it is non-null. When a local attacker issues a crafted request through the WinSock interface, the driver reaches the unchecked dereference and operates on attacker-influenced kernel memory.
The afd.sys driver is a recurring target for local privilege escalation research because it is reachable from any authenticated session and exposes a broad IOCTL surface. Successful exploitation transitions the caller from a standard user context to SYSTEM, providing full control over the host.
Root Cause
The root cause is a missing null check on a pointer used inside a kernel routine within afd.sys [CWE-476]. Under specific request sequencing or state conditions, the referenced object is not initialized or has already been released, leaving the pointer null when the driver subsequently accesses it. The dereference occurs at kernel privilege, allowing the attacker to influence execution flow rather than causing a simple bug check.
Attack Vector
Exploitation requires local, authenticated access to the target system. An attacker with a standard user account interacts with afd.sys through the WinSock API or directly via DeviceIoControl calls. By crafting a specific sequence of IOCTLs and object states, the attacker forces the driver into the vulnerable code path and leverages the null pointer condition to corrupt kernel state or hijack control flow, ultimately elevating to SYSTEM.
No synthetic proof-of-concept code is reproduced here. Refer to the Microsoft Security Update Guide for CVE-2025-53141 for vendor-supplied technical context.
Detection Methods for CVE-2025-53141
Indicators of Compromise
- Unexpected SYSTEM-owned processes spawned by child chains that originate from a standard user session.
- Kernel bug checks (BSODs) referencing afd.sys on hosts missing the August 2025 cumulative update.
- Unusual token duplication or process handle access targeting lsass.exe or winlogon.exe from low-integrity processes.
Detection Strategies
- Hunt for local processes issuing high volumes of DeviceIoControl calls against \\.\Afd from non-administrative accounts.
- Correlate parent-child process anomalies where a standard user process is followed by SYSTEM-integrity child processes.
- Baseline WinSock-related driver crashes and alert on new afd.sys faults on patched builds, which may indicate exploitation attempts.
Monitoring Recommendations
- Ingest Windows kernel and Sysmon telemetry (Event IDs 1, 10, and 25) into a centralized data lake for cross-host correlation.
- Track patch compliance for the August 2025 Microsoft security rollup across all Windows and Windows Server assets.
- Monitor for privilege escalation behaviors mapped to MITRE ATT&CK T1068 (Exploitation for Privilege Escalation).
How to Mitigate CVE-2025-53141
Immediate Actions Required
- Apply the Microsoft security update referenced in the MSRC advisory for CVE-2025-53141 to all affected Windows client and server builds.
- Prioritize patching of multi-user systems, jump hosts, and terminal servers where local accounts are most exposed.
- Audit local account inventories and remove unnecessary interactive logon rights to reduce the exploitable population.
Patch Information
Microsoft has released fixes through the standard Windows Update channel. Administrators should consult the Microsoft Security Update Guide entry for CVE-2025-53141 to identify the specific KB article for each affected Windows 10, Windows 11, and Windows Server release, then validate installation using Get-HotFix or the Windows Update history.
Workarounds
- No official vendor workaround is documented; installing the security update is the supported remediation.
- As defense-in-depth, restrict local logon rights and enforce application allowlisting to limit which binaries can invoke afd.sys IOCTLs.
- Enable attack surface reduction rules and standard user account controls to constrain post-exploitation activity even if the primitive is triggered.
# Verify the CVE-2025-53141 patch is installed (run in elevated PowerShell)
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 20
# Confirm the afd.sys driver file version after patching
Get-Item C:\Windows\System32\drivers\afd.sys | Select-Object VersionInfo
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
