CVE-2026-50312

What it actually does

This vulnerability is a use-after-free flaw in the Windows Ancillary Function Driver for WinSock, commonly associated with afd.sys. A low-privileged local user can trigger an invalid memory reuse condition in kernel-mode networking code. Successful exploitation may allow the attacker to influence freed kernel memory and potentially elevate privileges or cause a system crash, depending on exploit reliability and platform protections. The CVSS vector indicates local access, low privileges, no user interaction, high attack complexity, and high availability impact; public exploit maturity is currently reported as none and EPSS is low.

Why it matters to the business

The primary risk is that an attacker who already has local access to a Windows workstation or server could turn limited access into greater control or disrupt system availability. This is most relevant after an initial compromise, phishing foothold, malicious insider activity, or abuse of exposed interactive access such as RDP, VPN, or VDI. Because the affected range includes many Windows client and server versions, broad patch coverage matters even though this is not currently listed in CISA KEV, is not known to be used in ransomware campaigns, and has a low EPSS score.

How an attack unfolds

An attacker must first obtain the ability to run code locally with a low-privileged account on an affected Windows system. They then execute a specially crafted program that interacts with the Windows Ancillary Function Driver for WinSock through networking-related system calls or device interfaces. The exploit attempts to trigger a use-after-free condition in kernel memory by causing the driver to release an object and then access it again. If the attacker can shape kernel memory reliably, the condition may be abused to gain elevated privileges; if not, exploitation may result in a denial-of-service crash. No public exploit maturity is currently reported, so defenders should treat this primarily as a post-compromise privilege-escalation and stability risk rather than an internet-facing remote compromise path.

How to fix it

Apply the Microsoft security update that remediates this vulnerability for all affected Windows versions, including Windows 10, Windows 11, and Windows Server 2012 through Windows Server 2025 lines listed as affected. Because no fixed version details were provided in the input, use the latest cumulative update or security-only update available from Microsoft for the specific OS release and servicing channel. Prioritize systems that allow local interactive logon, RDP, VDI, shared administrative workstations, jump hosts, terminal servers, and servers exposed to untrusted users. If immediate patching is not possible, reduce risk by limiting local logon rights, restricting RDP and remote shell access, enforcing least privilege, blocking untrusted executable execution with application control, and monitoring for unusual local privilege escalation behavior. Avoid disabling core networking components such as afd.sys as a mitigation, because doing so may disrupt Windows networking functionality.

How to confirm the fix worked

Confirm each system is running the applicable Microsoft cumulative/security update released for this vulnerability or a later superseding update. Validate through Windows Update, WSUS, Microsoft Configuration Manager, Intune, or vulnerability management inventory. Check the installed OS build and patch level against Microsoft’s update guidance for the affected Windows release. Where feasible, verify that afd.sys has been updated to the expected patched file version for that OS build. Run authenticated vulnerability scans after patch deployment and confirm the finding is closed. Also verify that local privilege restrictions, RDP exposure controls, endpoint protection, and application control policies remain enforced on systems that cannot be patched immediately.

Typical attack path

1. Gain a local foothold on an affected Windows workstation or server using stolen credentials, malware execution, phishing, exposed remote access, or insider access.
2. Run a purpose-built local exploit process under a low-privileged user context.
3. Interact with Windows networking/WinSock kernel functionality handled by the Ancillary Function Driver.
4. Trigger the use-after-free condition by manipulating object allocation and release timing.
5. Attempt to reuse or corrupt freed kernel memory to execute privileged actions or destabilize the system.
6. Use elevated privileges, if obtained, to disable defenses, dump credentials, install persistence, or move laterally.

How to detect it

Look for evidence of local exploitation attempts rather than network-based scanning, because exploitation requires local code execution. Relevant log sources include Windows Security logs, Sysmon, EDR telemetry, Windows Defender logs, PowerShell logs, service control logs, scheduled task logs, crash dumps, and Windows Error Reporting. Hunt for newly executed unsigned or suspicious binaries from user-writable paths, especially processes that immediately precede privilege changes, service creation, driver interaction, LSASS access, security control tampering, or system crashes. Review System logs for bugchecks or crashes implicating afd.sys. Examine memory dumps and minidumps for references to afd.sys, use-after-free style crashes, or unusual call stacks involving WinSock/AFD operations. Since no public exploit or stable IOC is provided, detection should focus on behavioral indicators: local exploit execution, anomalous kernel crash artifacts, sudden privilege escalation, and post-exploitation actions after a low-privileged logon.

• afd.sys
• \\Device\\Afd
• \SystemRoot\System32\drivers\afd.sys
• C:\Windows\System32\drivers\afd.sys
• BugCheck
• afd.sys+
• Afd
• Ancillary Function Driver for WinSock
• SeDebugPrivilege
• net localgroup administrators
• sc.exe create
• schtasks.exe /Create
• whoami /priv
• C:\Windows\Minidump\
• MEMORY.DMP

What your security team should do

• Patch affected Windows clients and servers through the latest applicable Microsoft cumulative/security update, prioritizing systems with interactive user access, remote administration exposure, and shared multi-user workloads.
• Treat this as a post-compromise local privilege-escalation risk: review controls that prevent untrusted local code execution, including application control, EDR prevention, macro/script restrictions, and least-privilege enforcement.
• Harden and monitor RDP, VPN, VDI, jump servers, developer workstations, and terminal servers because local privilege escalation flaws become more valuable once an attacker obtains a foothold.
• Create detection logic for suspicious low-privileged processes interacting with kernel networking device interfaces followed by privilege changes, service creation, credential dumping, or security tool tampering.
• Investigate unexplained bugchecks or crashes involving afd.sys, especially if preceded by execution from user-writable directories such as Downloads, Temp, AppData, or ProgramData.
• Because the vulnerability is not currently KEV-listed, has no known ransomware use, and has low EPSS, prioritize after actively exploited internet-facing issues unless the organization has high exposure to local multi-user Windows systems.