CVE-2025-62217 Overview
CVE-2025-62217 is a race condition vulnerability in the Windows Ancillary Function Driver for WinSock (afd.sys). The flaw arises from concurrent execution using a shared resource with improper synchronization [CWE-362]. An authorized local attacker can exploit this condition to elevate privileges on affected Windows systems. Microsoft published the advisory on November 11, 2025, covering client editions from Windows 10 1607 through Windows 11 25H2 and server editions from Windows Server 2008 through Windows Server 2025. The vulnerability requires local access and low privileges but no user interaction, and successful exploitation compromises confidentiality, integrity, and availability of the target host.
Critical Impact
A local attacker with low-privilege access can win a race condition in afd.sys to escalate to SYSTEM, achieving full kernel-level control of the affected Windows host.
Affected Products
- Microsoft Windows 10 (1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (23H2, 24H2, 25H2)
- Microsoft Windows Server 2008, 2012, 2016, 2019, 2022, 2022 23H2, and 2025
Discovery Timeline
- 2025-11-11 - CVE-2025-62217 published to NVD
- 2026-06-17 - Last updated in NVD database
Technical Details for CVE-2025-62217
Vulnerability Analysis
The Ancillary Function Driver for WinSock (afd.sys) is the kernel-mode component that services user-mode WinSock socket operations. It handles I/O request packets (IRPs) issued by socket handles and manages internal state associated with each socket. The driver runs in kernel context, so any memory-safety violation in its code path directly impacts kernel integrity.
CVE-2025-62217 stems from improper synchronization when multiple threads access a shared socket resource concurrently. A local attacker with a valid user session can issue overlapping WinSock ioctl operations from separate threads. When the operations race, the driver observes an inconsistent object state, leading to a memory-safety violation that the attacker can convert into arbitrary kernel read/write primitives.
Root Cause
The root cause is a missing or insufficient lock around a shared socket structure inside afd.sys. One thread mutates or frees an object while another thread references the same object without exclusive access. This time-of-check to time-of-use pattern violates the atomicity requirements for kernel object lifetime management.
Attack Vector
Exploitation requires local code execution as an authenticated user. The attacker opens one or more WinSock sockets and dispatches parallel DeviceIoControl calls to \Device\Afd from multiple threads. By tuning thread timing, the attacker forces the vulnerable code path to execute concurrently and corrupts kernel state. The resulting primitive is typically weaponized to overwrite a token or process structure and execute code as SYSTEM. The high attack complexity reflects the timing sensitivity required to win the race consistently. No user interaction is required, and no network access is needed.
No public proof-of-concept was available at the time of publication, and the vulnerability is not listed in the CISA Known Exploited Vulnerabilities catalog. See the Microsoft Security Update Guide entry for CVE-2025-62217 for vendor technical detail.
Detection Methods for CVE-2025-62217
Indicators of Compromise
- Unexpected SYSTEM-level processes spawned from a user-context parent process shortly after high-volume WinSock activity
- Kernel bugchecks or system stability issues (for example, BAD_POOL_HEADER, KERNEL_MODE_HEAP_CORRUPTION) originating in afd.sys
- Unsigned or newly written binaries executing with elevated tokens on hosts missing the November 2025 cumulative update
Detection Strategies
- Hunt for user-mode processes issuing large volumes of concurrent NtDeviceIoControlFile calls against \Device\Afd from multiple threads
- Correlate token-elevation events (Sysmon Event ID 1 or Security Event ID 4688 with an elevated integrity level) that follow socket-heavy activity from the same parent process
- Alert on child processes inheriting a SYSTEM token from a non-service, non-administrative parent
Monitoring Recommendations
- Enable Sysmon with process creation, thread creation, and driver load logging, and forward events to a centralized analytics platform
- Monitor WER and minidump directories for repeated crashes referencing afd.sys frames
- Track deployment status of the November 2025 Windows security updates across the fleet and flag unpatched endpoints
How to Mitigate CVE-2025-62217
Immediate Actions Required
- Apply the November 2025 Microsoft security updates that address CVE-2025-62217 across all supported Windows client and server SKUs
- Prioritize patching on multi-user hosts such as Remote Desktop Session Hosts, Citrix servers, and shared jump boxes where local users are present
- Audit local administrator and standard user accounts on unpatched hosts and remove unnecessary interactive logon rights
Patch Information
Microsoft released fixes as part of the November 11, 2025 security update cycle. Refer to the Microsoft Security Update Guide for CVE-2025-62217 for the specific KB numbers matching each affected Windows build. Install cumulative updates through Windows Update, WSUS, Microsoft Update Catalog, or your endpoint management tool.
Workarounds
- No official workaround exists; Microsoft's guidance is to install the security update
- Restrict interactive and Remote Desktop logon to trusted administrators to reduce the local attacker surface until patching is complete
- Enable attack surface reduction and driver block-list enforcement to limit an attacker's ability to load supporting tooling required for exploitation
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
