Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local post-access EoP requiring a low-privilege authenticated context (AV:L/PR:L), no user interaction, reliable UAF trigger (AC:L), yielding full SYSTEM control (C/I/A:H).
Primary rating from Vendor (microsoft).
CVSS VectorNVD
Lifecycle Timeline
5DescriptionNVD
Use after free in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.
AnalysisAI
Local privilege escalation in the Windows Ancillary Function Driver for WinSock (afd.sys) allows an authenticated low-privileged attacker to gain SYSTEM-level control by triggering a use-after-free condition in the kernel networking driver. The flaw affects a broad range of Windows client and server releases from Windows 10 1607 through Windows 11 26H1 and Windows Server 2012 through Server 2025. Reported by Microsoft with a vendor patch available; no public exploit identified at time of analysis, and EPSS exploitation probability is low (0.31%).
Technical ContextAI
The Ancillary Function Driver (AFD.sys) is the kernel-mode driver that underpins the Windows Sockets (WinSock) API, mediating user-mode socket calls into the transport stack. It is a long-standing, high-value privilege-escalation target because it is reachable from unprivileged user code yet executes in kernel context. The root cause is CWE-416 (Use After Free): the driver continues to reference a kernel object after it has been freed, allowing a crafted sequence of socket operations to reclaim and manipulate the stale allocation. Controlling the freed object's memory lets an attacker corrupt kernel structures and redirect execution or falsify security tokens.
RemediationAI
Apply the Microsoft security update for CVE-2026-50312 via the MSRC Update Guide (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-50312); patch to at least the fixed builds for your edition - for example Windows 11 24H2 10.0.26100.8875, Windows 10 22H2 10.0.19045.7548, Windows Server 2022 10.0.20348.5386, Server 2025 10.0.26100.33158, Server 2019 10.0.17763.9020, Server 2016/10.0.14393.9339, Server 2012 6.2.9200.26226, and Server 2012 R2 6.3.9600.23291. Vendor-released patch is available and is the definitive fix. Because afd.sys is a core kernel component with no configuration toggle, there is no clean disable-the-feature workaround; the practical compensating controls are to enforce least privilege so untrusted users cannot run arbitrary code locally, apply application allowlisting to block unknown binaries, and enable attack-surface-reduction and EDR kernel-exploit detections to catch UAF exploitation attempts. These controls reduce but do not eliminate risk and should be treated as interim measures until patching is complete.
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Same weakness CWE-416 – Use After Free
View allSame technique Memory Corruption
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External POC / Exploit Code
Leaving vuln.today
EUVD-2026-43888
GHSA-wq5v-h429-2627