EUVD-2026-99350
GHSA-r94g-2j35-fgc6
Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata – not a confirmed exploit chain
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AccessObtain low-privileged local code execution
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DeliveryRepeatedly invoke vulnerable AFD.sys WinSock path
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ExploitWin race to trigger use-after-free
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ExecutionReclaim freed kernel object
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PersistCorrupt kernel memory for execution
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ImpactElevate to SYSTEM privileges
Vulnerability Assessment
| Weakness |
CWE
OWASP Top 10:2025
A06:2025 - Insecure Design
ASVS 5.0
V15 - Secure Coding and Architecture Concurrency control, locking
MITRE ATT&CK
1 technique across 1 tactic: Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. |
| Exploitation Conditions | Requires the attacker to already have local, low-privileged authenticated code execution on the target (PR:L, AV:L) - there is no remote vector. The specific trigger is a use-after-free reached through a race condition (CWE-362, AC:H) in the Ancillary Function Driver for WinSock (AFD.sys); the attacker must repeatedly race the vulnerable socket-handling code path to win a narrow timing window, which is the primary limiting factor and makes exploitation unreliable and non-automatable (SSVC Automatable=no). No non-default configuration is needed - AFD.sys is present and loaded on all supported Windows client and server editions by default - but exploitation is realistically limited to scenarios where an attacker can run arbitrary code locally (multi-user hosts, post-foothold escalation). |
| Impact | Signals are consistent and point to a moderate, non-urgent patching priority. The CVSS 3.1 vector (AV:L/AC:H/PR:L/UI:N) describes a local, authenticated attack of high complexity - the attacker must already be able to run code on the host and must win a race-condition timing window, which caps the base score at 7.0 (High) despite total C:H/I:H/A:H impact (kernel-to-SYSTEM elevation). CISA's SSVC framework reinforces lower urgency: Exploitation=none (no observed activity), Automatable=no (consistent with the AC:H race that is hard to weaponize reliably), and Technical Impact=total (full compromise once triggered). No EPSS score, KEV listing, or public POC was provided, so there is no evidence of exploitation or exploit tooling at time of analysis. The main caveat: AFD.sys (the WinSock kernel driver) is a historically favored local-EoP target and is present on every Windows system, so while the race condition limits reliability, the ubiquity and total impact mean this should be patched on normal cycles and prioritized on multi-user or shared hosts where untrusted code runs. |
| Exploit ScenarioDerived | A local attacker who already has a low-privileged foothold (e.g., via phishing or a compromised service account) runs a program that repeatedly triggers the vulnerable WinSock/AFD.sys code path to win a race window and reuse freed kernel memory. Successful exploitation corrupts kernel objects to execute code in kernel context, elevating from a standard user to SYSTEM. No public exploit code was identified at time of analysis, and the high attack complexity (race condition) makes reliable exploitation difficult. |
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Alert meAnalysisAIv1 – Oct 13, 2026
Local privilege escalation in Microsoft Windows' Ancillary Function Driver for WinSock (AFD.sys) allows an authenticated, low-privileged attacker who already has local code execution to corrupt kernel memory and raise their privileges to kernel/SYSTEM level. The bug is a use-after-free reached by winning a race condition (CWE-362) in the socket-handling path, which is why it carries high attack complexity (AC:H) - exploitation requires repeatedly racing a narrow timing window and is unreliable and non-automatable (SSVC Automatable=no). Almost every supported Windows client and server build is affected because AFD.sys is loaded by default, but the practical exposure is limited to multi-user hosts or post-foothold escalation; vendor patches are available and no public exploit code or observed exploitation was identified at the time of analysis.
RemediationAI
Patch available per vendor advisory: install the latest Windows cumulative security update for each affected build, using the fixed build levels published in the MSRC update guide (https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-83738) - for example 10.0.14393.9612 for Windows 10 1607 / Server 2016, 10.0.17763.9376 for Windows 10 1809 / Server 2019, 10.0.19044.7807 for Windows 10 21H2/22H2, 10.0.22631.7652 for Windows 11 23H2, 10.0.26100.9711 for Windows 11 24H2, 10.0.26200.9711 for Windows 11 25H2, 10.0.28000.3231 for Windows 11 26H1, 10.0.26300.9711 for Windows 11 26H2, 10.0.20348.5761 for Server 2022, 10.0.26100.33650 for Server 2025, 6.3.9600.23470 for Server 2012 R2 and 6.2.9200.26434 for Server 2012; superseded platforms that no longer receive updates (notably Server 2012/2012 R2) should be migrated or isolated. Because the sole attack vector is local (AV:L) and requires pre-existing low-privileged code execution (PR:L), the effective compensating controls are those that shrink the local attacker's foothold: remove unnecessary interactive logon rights and local administrator membership, restrict RDP and other remote-interactive access to trusted administrative jump hosts (trade-off: reduced administrative convenience and potential operational friction for helpdesk workflows), and enforce least-privilege/AppLocker or WDAC policies that block untrusted binaries from executing on multi-user hosts and RDS/VDI session servers (trade-off: policy tuning effort and risk of blocking legitimate line-of-business applications). AFD.sys cannot be disabled or unloaded - it is required for all sockets - so there is no driver-level workaround, and kernel memory-corruption protections such as Credential Guard and HVCI reduce post-exploitation value rather than preventing the bug; the only complete fix is applying the vendor update and rebooting.
Affected VersionsENISA
Affected Packages
Source: OSV (Open Source Vulnerabilities)
Affects your stack
Affects 20 packages in euvd
Checking this CVE against your own stacks and servers is part of the Basic plan and up.
Technical ContextAI · show details
AFD.sys (the Ancillary Function Driver for WinSock, exposed as \Device\Afd) is the in-box kernel-mode driver that backs the Windows Winsock API, servicing socket creation, asynchronous I/O and poll/select-style operations for essentially every networked process on the system. The root cause class here is a race condition (CWE-362) in that driver: concurrent access to socket/AFD endpoint state can free an object while another thread still references it, producing a use-after-free on kernel memory. Because the freed object is reused in kernel context, a successful attacker can redirect execution or corrupt kernel structures and elevate from a low-privileged local process to SYSTEM. The CVSS vector CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H confirms this is strictly a local (AV:L), authenticated (PR:L), no-user-interaction (UI:N) issue with high confidentiality and integrity impact; the AC:H rating and the SSVC assessment (Exploitation: none, Automatable: no, Technical Impact: total) indicate the timing window is narrow and reliable exploitation is difficult. No non-default configuration is needed - AFD.sys is present and loaded on all affected editions out of the box - but the attacker must first hold a local foothold on the target.
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Severity by source
AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H
Local-only EoP requiring existing low-privileged code execution (AV:L/PR:L) and winning a race-condition window (AC:H); kernel compromise yields full SYSTEM control, so C/I/A are all High.
Primary rating from Vendor (microsoft).
CVSS VectorVendor: microsoft
Lifecycle Timeline
2DescriptionCVE.org
Use after free in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.
Executive ViewAI
A privilege-escalation flaw in the Microsoft Windows Ancillary Function Driver for WinSock (AFD.sys) affects nearly every supported Windows client and server build because the driver loads by default, allowing an attacker who already holds a foothold on a host to elevate to kernel/SYSTEM level. The practical risk is concentrated on multi-user systems such as RDP hosts, jump servers, and terminal servers, where a standard user account can become a full administrator and use that access for lateral movement or ransomware staging. No public exploit code or observed exploitation was identified at time of analysis, and a vendor patch is available, making this primarily a fleet-wide patch-management obligation rather than an emergency response.
Apply vendor patch.
Threat Intelligence Overview
NVD
CVE.org
EPSS
Vulnrichment
How this decision was reached
The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.
What every action level means
SSVC AssessmentENISA
Priority Score
Attack Technique
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