Microsoft Windows Ancillary Function Driver for WinSock Use-After-Free Vulnerability

Use after free in Windows Ancillary Function Driver for WinSock allows an authorized attacker to elevate privileges locally.

CheckOps priority index

4.3/10 Patch within 7 days

Severity7.0

Probability0.9

Exploitation2/5

Severity = CVSS. Probability = EPSS (FIRST). Exploitation = public signals: KEV, EUVD, ransomware, EPSS above 10 %, no account required.

EPSS · today 8.6% +8.2 pts in 7 days

CVSS 3.1 7.0 AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:

Exploited for 84 days 11 Aug 2026

CISA due date 25 Aug 2026 for US federal agencies

Exploitation probability EPSS · FIRST

EPSS probability (%)Percentile among all CVEs

Exploitation signals 2 / 5

KEV catalog (CISA)11 Aug 2026
Exploited in EUVD (ENISA)11 Aug 2026
Used by ransomwareno
EPSS above 10 %8.6%
No account, over the networkno

What to do

Fix

Apply the vendor’s fix as soon as it is available.

CISA guidance: Apply mitigations in accordance with vendor instructions, ensuring compliance with CISA’s BOD 26-04 Prioritizing Security Updates Based on Risk (see URL in Notes) guidance and CISA’s “Forensics Triage Requirements” (see URL in Notes). Follow applicable BOD 26-04 guidance for cloud services or discontinue use of the product if mitigations are unavailable. Stakeholders are responsible for evaluating each asset's internet exposure and ensuring adherence to BOD 26-04 patching guidelines.

Meanwhile

Take the service off the internet or restrict access to it, watch the logs and look for signs of compromise.

Manufacturers (CRA)

Exploited vulnerability in your product: early warning to ENISA within 24 h, then notification within 72 h (Article 14 of the Cyber Resilience Act). The CRA explained

Affected products

Windows 11 Version 24H2Windows Server 2022Windows Server 2012 R2Windows 10 Version 22H2Windows Server 2012Windows Server 2025 (Server Core installation)Windows 10 Version 21H2Windows Server 2016 (Server Core installation)Windows Server 2019 (Server Core installation)Windows 11 Version 25H2Windows Server 2016Windows Server 2019Windows 10 Version 1809Windows Server 2012 R2 (Server Core installation)Windows Server 2012 (Server Core installation)Windows Server 2025Windows 10 Version 1607Windows 11 Version 23H2Windows 11 version 26H1Windows Ancillary Function Driver for WinSock

Affected versions

10.0.26100.0 <10.0.26100.9168
10.0.20348.0 <10.0.20348.5499
6.3.9600.0 <6.3.9600.23338
10.0.19045.0 <10.0.19045.7663
6.2.9200.0 <6.2.9200.26280
10.0.26100.0 <10.0.26100.33296
10.0.19044.0 <10.0.19044.7663
10.0.14393.0 <10.0.14393.9418
10.0.17763.0 <10.0.17763.9121
10.0.26200.0 <10.0.26200.9168
10.0.22631.0 <10.0.22631.7517
10.0.28000.0 <10.0.28000.2704

Weaknesses (CWE)

CWE-416

Open source packages OSV

Affected libraries according to OSV, with fixed versions.

Timeline

11 Aug 2026
Published
11 Aug 2026
Exploitation reported (ENISA)
11 Aug 2026
Added to the KEV catalog
25 Aug 2026
CISA remediation due date

References

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