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CVE-2025-21418: Microsoft Windows Ancillary Function Driver for WinSock Heap-Based Buffer Overflow Vulnerability

criticalknown exploitedCVE-2025-21418
Actively exploited. At least one CVE in this advisory is listed in the CISA Known Exploited Vulnerabilities catalog — exploitation has been observed in the wild. Treat remediation as urgent.
Microsoft Windows Ancillary Function Driver for WinSock contains a heap-based buffer overflow vulnerability that allows for privilege escalation, enabling a local attacker to gain SYSTEM privileges.

CSIRTS triage

vendor: Microsoftproduct: Windows Ancillary Function Driver for WinSockPrivilege escalationOther
What
A heap-based buffer overflow vulnerability in the Windows Ancillary Function Driver for WinSock allows for privilege escalation.
Who is affected
Local attackers on systems running the affected Windows version.
Urgency
Immediate action is required due to active exploitation and critical severity.
Action
Install the latest security updates for Microsoft Windows.

AI-assisted analysis generated from the source advisory — verify against the original.

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Details

Source
CISA Known Exploited Vulnerabilities (US · database · site)
Severity
critical
Published
2025-02-11
Exploitation
Observed in the wild (CISA KEV)

Original advisory: https://nvd.nist.gov/vuln/detail/CVE-2025-21418

Exploitation outlook

EPSS (FIRST.org) estimates each CVE’s probability of exploitation in the next 30 days — here is the CSIRTS.com read on those numbers.

Referenced CVEs

CVECSIRTS overviewExternal
CVE-2025-21418coverage & exploitation statusNVD · CVE.org

Recent advisories for Microsoft Windows Ancillary

A cluster of recent advisories against the same product widens the attack surface — attackers routinely chain freshly published CVEs on one product, so review these together.

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