CVE-2026-50312 Overview
CVE-2026-50312 is a use-after-free vulnerability [CWE-416] in the Windows Ancillary Function Driver for WinSock (afd.sys). The flaw allows an authorized local attacker to elevate privileges to SYSTEM on affected Windows client and server platforms. Microsoft published the advisory on July 14, 2026, and the vulnerability affects a broad range of supported Windows versions, including Windows 10, Windows 11, and Windows Server 2012 through 2025.
Exploitation requires low privileges and no user interaction. Successful attacks yield full confidentiality, integrity, and availability impact on the target host. The afd.sys driver has historically been a target for local privilege escalation, and this issue continues that pattern.
Critical Impact
A local, authenticated attacker can escalate to kernel-level privileges, gaining full control over the affected Windows host.
Affected Products
- Microsoft Windows 10 (1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (24H2, 25H2, 26H1)
- Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, 2025
Discovery Timeline
- 2026-07-14 - CVE-2026-50312 published to NVD and Microsoft security advisory released
- 2026-07-16 - Last updated in NVD database
Technical Details for CVE-2026-50312
Vulnerability Analysis
The vulnerability resides in the Ancillary Function Driver for WinSock, afd.sys. This kernel-mode driver is the transport interface between user-mode Winsock calls and the Windows TCP/IP stack. Any authenticated local user can open a handle to the driver through the standard Winsock API, which makes the driver a persistent attack surface for local privilege escalation.
The issue is a use-after-free condition [CWE-416]. Kernel code releases an object while another code path retains a reference to it. Subsequent operations on the dangling pointer allow an attacker to manipulate freed memory that has been reallocated with controlled content. The attacker leverages this to corrupt kernel structures and hijack execution flow in ring 0.
Root Cause
Use-after-free defects in afd.sys typically stem from missing reference counting or race conditions between asynchronous I/O completions and cleanup routines. When the driver frees an object without invalidating all outstanding references, later access reads or writes attacker-controlled data placed in the reclaimed allocation.
Attack Vector
The attack requires local access with valid credentials. An attacker running arbitrary code as a low-privileged user issues a crafted sequence of Winsock IOCTLs against \Device\Afd. By racing allocation and free operations and spraying the kernel pool with controlled objects, the attacker converts the freed slot into a controllable primitive. The final payload typically overwrites a token pointer or modifies the process security context to grant SYSTEM privileges.
No verified public proof-of-concept is available for CVE-2026-50312. Refer to the Microsoft Security Update CVE-2026-50312 advisory for technical guidance.
Detection Methods for CVE-2026-50312
Indicators of Compromise
- Unexpected processes spawning with SYSTEM or elevated tokens from parent processes running under standard user accounts.
- Kernel crashes or bug checks referencing afd.sys in crash dumps, particularly BAD_POOL_HEADER or KERNEL_MODE_HEAP_CORRUPTION errors.
- Anomalous handle opens to \Device\Afd followed by unusual IOCTL sequences from non-network applications.
Detection Strategies
- Monitor for token manipulation and access token duplication events tied to child processes that inherit SYSTEM privileges from lower-integrity parents.
- Alert on process integrity level transitions from Medium or Low to System without a legitimate elevation event.
- Correlate driver load telemetry and kernel exception events with local user session activity to surface exploitation attempts.
Monitoring Recommendations
- Enable Windows Defender Application Control or WDAG policies to block unsigned or unauthorized executables from running as standard users.
- Ingest Sysmon Event ID 10 (ProcessAccess) and Event ID 1 (ProcessCreate) into your SIEM to detect abnormal parent-child relationships involving lsass.exe or services.exe.
- Track EDR telemetry for repeated NtDeviceIoControlFile calls targeting the AFD device object from unusual process contexts.
How to Mitigate CVE-2026-50312
Immediate Actions Required
- Apply the July 2026 Microsoft security updates to all affected Windows client and server systems without delay.
- Prioritize patching multi-user hosts, terminal servers, and jump boxes where local authenticated access is most common.
- Audit local account membership and remove unnecessary interactive logon rights to reduce the attacker pool.
Patch Information
Microsoft has released cumulative updates addressing CVE-2026-50312 across all supported Windows versions. Consult the Microsoft Security Update CVE-2026-50312 advisory for KB numbers matching each affected product and architecture.
Workarounds
- No official workaround exists. Microsoft recommends applying the security update as the only supported remediation.
- Restrict local logon and remote desktop access to trusted administrators to limit exposure until patches are deployed.
- Enforce application allow-listing to block execution of untrusted binaries that could carry exploit payloads.
# Verify installed KB updates on Windows hosts
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10
# Query current build to confirm patch level
[System.Environment]::OSVersion.Version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
