CVE-2025-49762 Overview
CVE-2025-49762 is a race condition vulnerability in the Windows Ancillary Function Driver for WinSock (afd.sys). The flaw allows an authenticated local attacker to elevate privileges to SYSTEM by exploiting improper synchronization of shared kernel resources [CWE-362]. Microsoft addressed the issue in the August 2025 Patch Tuesday release. The vulnerability affects a broad range of Windows client and server platforms, including Windows 10, Windows 11, and Windows Server versions from 2008 through 2025.
Critical Impact
Successful exploitation grants an authorized local attacker SYSTEM-level privileges on affected Windows hosts, enabling full compromise of the operating system.
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-2025-49762 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-49762
Vulnerability Analysis
The vulnerability resides in the Ancillary Function Driver for WinSock (afd.sys), the kernel-mode driver that backs the Windows Sockets API. A race condition [CWE-362] occurs when concurrent threads access a shared resource without proper synchronization. An attacker who can execute code locally with low privileges can trigger this window to manipulate kernel state.
Exploitation requires precise timing, which explains the high attack complexity in the CVSS vector. When the race is won, the attacker gains code execution in the kernel context. This escalates privileges from a standard user to SYSTEM.
Root Cause
The root cause is improper synchronization on a shared object inside afd.sys. Two or more threads issuing overlapping I/O control operations can reach a code path where one thread references or frees a structure that another thread modifies. This creates a time-of-check to time-of-use (TOCTOU) condition that corrupts kernel memory or produces an unexpected privileged operation.
Attack Vector
The attack vector is local. The attacker must already be authenticated on the target system and able to run code, for example through an interactive session, RDP, or a compromised low-privileged service. The attacker opens handles to the AFD device and issues concurrent I/O requests designed to trigger the race window. Because no user interaction is required, the vulnerability is well-suited as a second-stage payload chained with a remote code execution primitive or a phishing-delivered loader. No public proof-of-concept or in-the-wild exploitation has been reported at this time, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog.
See the Microsoft CVE-2025-49762 Advisory for vendor-provided technical details.
Detection Methods for CVE-2025-49762
Indicators of Compromise
- Unexpected child processes spawned by low-privileged accounts running as NT AUTHORITY\SYSTEM.
- Unusual token manipulation or process handle duplication targeting lsass.exe or services.exe shortly after AFD I/O activity.
- Presence of unsigned or newly compiled binaries in user-writable directories immediately preceding a privilege change event.
Detection Strategies
- Hunt for processes that open handles to \Device\Afd and issue high volumes of NtDeviceIoControlFile calls in a tight loop, which can indicate race-window brute-forcing.
- Correlate Windows Security event ID 4672 (special privileges assigned) with a preceding low-integrity process launch from the same user session.
- Alert on kernel crashes or bugchecks referencing afd.sys on production hosts, since failed exploitation attempts frequently produce driver faults.
Monitoring Recommendations
- Enable process creation auditing (event ID 4688) with command-line logging across all endpoints and servers.
- Forward Sysmon and Windows kernel telemetry to a centralized SIEM or data lake for retrospective hunting.
- Baseline normal AFD driver usage and flag statistical outliers in I/O control code volume per process.
How to Mitigate CVE-2025-49762
Immediate Actions Required
- Apply the August 2025 Microsoft security updates that patch afd.sys on all affected Windows client and server systems.
- Prioritize patching multi-user hosts, terminal servers, VDI infrastructure, and jump servers where local code execution is more likely.
- Audit local user accounts and remove unnecessary interactive logon rights to reduce the population of potential attackers.
Patch Information
Microsoft released the fix through the standard Windows Update channel on 12 August 2025. Administrators should consult the Microsoft CVE-2025-49762 Advisory to identify the specific KB article for each Windows build in their environment and confirm installation using Get-HotFix or WSUS reporting.
Workarounds
- No official workaround exists; installing the Microsoft security update is the only supported remediation.
- Restrict local logon and remote interactive sessions to trusted administrative users until patches are deployed.
- Apply application allowlisting to prevent execution of unknown binaries from user-writable paths, limiting the ability to stage an exploit.
# Verify the AFD-related update is installed (example PowerShell)
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 20
# Confirm afd.sys file version against the patched build listed in the Microsoft advisory
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.
