CVE-2026-24293 Overview
CVE-2026-24293 is a null pointer dereference vulnerability [CWE-476] in the Windows Ancillary Function Driver for WinSock (afd.sys). An authorized local attacker can exploit the flaw to elevate privileges on affected Windows systems. Microsoft published the advisory through the Microsoft Security Response Center (MSRC) Update Guide.
The vulnerability affects supported Windows 10, Windows 11, and Windows Server releases. Exploitation requires local access and low-privileged authentication. Successful exploitation produces high impact on confidentiality, integrity, and availability of the targeted host.
Critical Impact
A low-privileged local user can leverage the flaw in afd.sys to gain SYSTEM-level privileges, enabling full host compromise.
Affected Products
- Microsoft Windows 10 21H2 and 22H2 (x86, x64, ARM64)
- Microsoft Windows 11 23H2, 24H2, 25H2, and 26H1 (x64, ARM64)
- Microsoft Windows Server 2022, Windows Server 2022 23H2, and Windows Server 2025
Discovery Timeline
- 2026-03-10 - CVE-2026-24293 published to NVD
- 2026-03-13 - Last updated in NVD database
Technical Details for CVE-2026-24293
Vulnerability Analysis
The vulnerability resides in the Windows Ancillary Function Driver for WinSock, commonly referenced as afd.sys. The driver provides the kernel-mode interface that the Winsock user-mode library uses to service socket operations. A code path within the driver dereferences a pointer without validating that the pointer is non-null. When an attacker reaches that code path with a crafted I/O request, the kernel operates on an invalid address.
Null pointer dereferences in kernel drivers typically cause a system crash. In this case, the flaw is classified as an elevation of privilege issue rather than a denial of service. This indicates that the dereferenced memory region can be influenced by the caller, allowing controlled access to kernel structures and a path to executing attacker-controlled logic in kernel context.
Root Cause
The root cause is missing validation of a pointer value before use, mapped to [CWE-476] Null Pointer Dereference. The afd.sys driver handles I/O Request Packets (IRPs) from user mode through DeviceIoControl and socket APIs. A specific request flow returns a path where a required object pointer is not initialized or has been freed, and the driver proceeds to operate on it.
Attack Vector
Exploitation requires local access and a low-privileged authenticated session. The attacker opens a handle to the AFD device and issues a sequence of I/O control codes that drive the driver into the vulnerable state. No user interaction is needed. Because Winsock is loaded on every supported Windows release, the attack surface is present across both desktop and server SKUs listed in the advisory.
No public proof-of-concept code or exploit is referenced in the advisory. See the Microsoft CVE-2026-24293 Update Guide for vendor technical details.
Detection Methods for CVE-2026-24293
Indicators of Compromise
- Unexpected child processes of low-privileged user sessions running as NT AUTHORITY\SYSTEM.
- Kernel bug check events (BSOD) referencing afd.sys followed by token or process integrity changes.
- Newly created services, scheduled tasks, or local accounts immediately after suspicious afd.sys activity.
- Unsigned or unusual binaries opening handles to \\Device\\Afd from non-network workloads.
Detection Strategies
- Monitor for token manipulation patterns where a process duplicates or steals a SYSTEM token after interacting with the AFD device.
- Hunt for sequences of NtDeviceIoControlFile calls targeting AFD I/O control codes from non-network applications.
- Correlate kernel crash telemetry referencing afd.sys with subsequent privilege escalation indicators on the same host.
Monitoring Recommendations
- Forward Windows Security, System, and kernel crash logs to a centralized analytics platform for cross-host correlation.
- Alert on process integrity level transitions from Medium to System without a known parent service.
- Track patch compliance for afd.sys versions across the fleet to identify unpatched endpoints.
How to Mitigate CVE-2026-24293
Immediate Actions Required
- Apply Microsoft's security updates for all affected Windows 10, Windows 11, and Windows Server versions referenced in the MSRC advisory.
- Prioritize patching multi-user systems, terminal servers, jump hosts, and developer workstations where untrusted local code is more likely to run.
- Restrict local logon rights and remove unnecessary interactive accounts on servers.
Patch Information
Microsoft has released security updates through the standard Windows Update channels. Refer to the Microsoft CVE-2026-24293 Update Guide for the build numbers and KB article associated with each affected Windows release. Install the corresponding cumulative update on each system.
Workarounds
- No vendor-supplied workaround is published. Apply the security update as the primary remediation.
- Reduce exposure by enforcing least privilege and blocking execution of untrusted binaries through application control policies such as Windows Defender Application Control or AppLocker.
- Enable attack surface reduction rules and tamper protection to limit post-exploitation activity if a local user attempts to leverage the flaw.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
