CVE-2026-57093 Overview
CVE-2026-57093 is a use-after-free vulnerability [CWE-416] in the Windows Ancillary Function Driver for WinSock (afd.sys). The flaw allows an authenticated local attacker to elevate privileges to SYSTEM on affected Windows client and server operating systems. Microsoft published the advisory on July 14, 2026, covering all supported Windows 10, Windows 11, and Windows Server releases. The Ancillary Function Driver is a kernel-mode component that provides support for Windows Sockets applications, making it a frequent target for local privilege escalation research.
Critical Impact
Successful exploitation grants kernel-level code execution, enabling full compromise of confidentiality, integrity, and availability on the affected host.
Affected Products
- Microsoft Windows 10 (versions 1607, 1809, 21H2, 22H2)
- Microsoft Windows 11 (versions 24H2, 25H2, 26H1)
- Microsoft Windows Server 2012, 2012 R2, 2016, 2019, 2022, and 2025
Discovery Timeline
- 2026-07-14 - Microsoft publishes security advisory for CVE-2026-57093
- 2026-07-14 - CVE-2026-57093 published to NVD
- 2026-07-17 - Last updated in NVD database
Technical Details for CVE-2026-57093
Vulnerability Analysis
The Ancillary Function Driver for WinSock, implemented in afd.sys, exposes kernel-mode support routines that user-mode socket APIs rely on. A use-after-free condition [CWE-416] in this driver permits a low-privileged local user to reference kernel memory after it has been freed. Once the freed allocation is reclaimed with attacker-controlled data, the reused pointer leads to controlled kernel-mode execution.
Attackers can leverage this primitive to overwrite kernel structures such as process tokens, replacing the caller's token with that of a SYSTEM process. This is a well-established local privilege escalation pattern for afd.sys vulnerabilities.
Root Cause
The defect stems from improper lifetime management of an object allocated by the driver. The driver retains or dereferences a pointer to an object after the object has been released back to the pool. Concurrent I/O operations against socket handles create a window in which the freed memory can be reallocated and populated with attacker-controlled content before the stale pointer is used.
Attack Vector
Exploitation requires local access and the ability to execute code with standard user privileges. No user interaction is required. The attacker interacts with the driver through documented socket APIs and I/O control codes, triggering the vulnerable code path and then racing to reclaim the freed allocation. Successful exploitation yields kernel-mode execution and full SYSTEM privileges on the target host.
No public proof-of-concept exploit or in-the-wild exploitation has been reported at the time of publication. See the Microsoft CVE-2026-57093 Advisory for vendor technical details.
Detection Methods for CVE-2026-57093
Indicators of Compromise
- Unexpected token replacement events where a non-administrative process suddenly executes with NT AUTHORITY\SYSTEM privileges.
- Kernel bug checks (BSOD) referencing afd.sys, particularly BAD_POOL_CALLER or KERNEL_MODE_HEAP_CORRUPTION.
- Unsigned or unusual child processes spawned by services running under low-privileged accounts following heavy socket I/O activity.
Detection Strategies
- Monitor for process integrity level transitions from Medium to System without a corresponding legitimate elevation (UAC prompt, scheduled task, or service start).
- Alert on suspicious loads and interactions with \Device\Afd from processes that do not typically perform low-level socket operations.
- Correlate creation of privileged child processes with prior high-volume IOCTL traffic to the AFD driver from the same parent process.
Monitoring Recommendations
- Enable Windows kernel-mode auditing and centralize System and Security event logs for retrospective hunting.
- Track patch state for afd.sys across the fleet and flag hosts running unpatched builds after the July 2026 update.
- Baseline normal socket API usage per host role and alert on statistical outliers, which can indicate exploitation attempts against race conditions.
How to Mitigate CVE-2026-57093
Immediate Actions Required
- Apply the July 2026 Microsoft security updates to all affected Windows client and server systems without delay.
- Prioritize patching multi-user systems, terminal servers, and jump hosts where low-privileged local access is expected.
- Audit local account inventory and remove unnecessary interactive logon rights to reduce the pool of potential attackers.
Patch Information
Microsoft has released patches through the standard Windows Update channel. Refer to the Microsoft CVE-2026-57093 Advisory for the specific KB article and updated afd.sys build number corresponding to each affected Windows version.
Workarounds
- No official workaround has been published by Microsoft; installing the security update is the only supported remediation.
- Enforce least-privilege policies and application allowlisting to limit the ability of unauthorized binaries to execute and interact with the driver.
- Restrict local logon and Remote Desktop access on high-value systems until patches are deployed.
# Verify patch deployment via PowerShell
Get-HotFix | Sort-Object -Property InstalledOn -Descending | Select-Object -First 10
Get-Item C:\Windows\System32\drivers\afd.sys | Select-Object Name, VersionInfo
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
