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CVE-2026-70307 is a use-after-free (UAF) vulnerability identified in the Windows Ancillary Function Driver (AFD) for WinSock. AFD.sys is a core kernel-mode driver that manages socket operations and network I/O for the Winsock API. The flaw stems from improper handling of local requests, where the driver fails to properly track object references during certain operations. When a local, authenticated attacker sends a specially crafted sequence of requests, they can trigger a race condition that causes the driver to reference memory that has already been freed.
The vulnerability exists because the driver reuses or references memory after it has been deallocated. At some point after the memory is freed, it may be reallocated for a different purpose. If the driver continues to use the original pointer, it will operate on memory containing attacker-controlled data. This classic resource reuse issue is classified as CWE-416. An attacker who successfully exploits this vulnerability can execute arbitrary code with the privileges of the calling process, ultimately leading to SYSTEM-level privilege escalation. Microsoft has reported this vulnerability as “Exploitation Detected,” indicating active exploitation attempts in the wild.
DailyCVE Form:
Platform: Windows 10/11/Server
Version: Multiple (see below)
Vulnerability: Use-After-Free (CWE-416)
Severity: 7.0 HIGH
Date: August 11, 2026
Prediction: August 2026 Patch Tuesday
What Undercode Say:
Check if the system is vulnerable by verifying the build number systeminfo | findstr /B "OS Name OS Version" Check for the presence of the vulnerable AFD.sys driver driverquery /v | findstr /i "afd.sys" Verify installed update status for the August 2026 Patch Tuesday wmic qfe list brief /format:table | findstr "KB5034763"
Exploit: (Educational Purposes!)
// Conceptual trigger for the race condition - EDUCATIONAL USE ONLY HANDLE hSocket = socket(AF_INET, SOCK_STREAM, 0); // Send malformed IOCTL to AFD.sys to free the object DeviceIoControl(hSocket, IOCTL_AFD_FREE_OBJECT, ...); // Race condition: trigger reuse of freed memory before reallocation DeviceIoControl(hSocket, IOCTL_AFD_USE_FREED_OBJECT, ...);
Protection:
- Install the Microsoft security update for CVE-2026-70307 as published on the Microsoft Security Update Guide
- Affected versions addressed: Windows 10 21H2 (10.0.19044.7663), 22H2 (10.0.19045.7663), 1607 (10.0.14393.9418), 1809 (10.0.17763.9115); Windows 11 23H2 (10.0.22631.7517), 24H2 (10.0.26100.9106/9168), 25H2 (10.0.26200.9168), 26H1 (10.0.28000.2704); Windows Server 2012 R2 (6.3.9600.23337), 2012 (6.2.9200.26279), 2016 (10.0.14393.9418), 2019 (10.0.17763.9115), 2022 (10.0.20348.5440/5499), 2025 (10.0.26100.33222/33296)
- Reboot affected systems to ensure the driver update is fully applied
- Enable Windows Update to receive future patches automatically
Impact:
Successful exploitation allows a local, authorized attacker to elevate privileges to SYSTEM level. The vulnerability requires local access and high attack complexity. The CVSS 3.1 base score is 7.0 (HIGH) with vector AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H. All supported Windows client and server versions are affected.
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Sources:
Reported By: nvd.nist.gov
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