Threats / Microsoft / CVE-2025-21418
CVE-2025-21418
· EUVD no mirror located
· GCVE no mirror located
Verified 2026-06-22
Microsoft Windows vulnerability
A heap-based buffer overflow in Windows Ancillary Function Driver for WinSock allows local attackers to escalate privileges to SYSTEM level.
Verdict
Today item — known-exploited.
This vulnerability enables privilege escalation from a local context to SYSTEM, granting complete system control. Active exploitation in the wild increases risk. Patch deployment is critical for all affected Windows systems.
01
Is it exploitable?
— the evidence, ranked above the scoreReported exploitation
5 independent public reports of in-the-wild exploitation are cataloged.Distinct reporting sources (vendor, incident response, government); open them for the underlying claims.
Exploited in the wild
Listed in the CISA Known Exploited Vulnerabilities catalog (added 2025-02-11).
Probability (EPSS)
EPSS 0.01459 — modeled likelihood of exploitation activity.EPSS is a daily-changing model output — open the source for today's value.
Severity / affected
Affected: Microsoft, Windows. Confirm exact fixed builds in the vendor advisory.
Weakness (CWE)
Mapped to CWE-122 Heap-based Buffer Overflow — weakness family: Memory safety.CWE assignment from the public NVD record; the weakness class drives how the flaw is exploited.
02
Who’s exploiting it?
— attribution turns risk into urgencyAttribution not established
No confirmed (advisory-backed) threat-actor attribution is established for this record. Absence of a named actor is not absence of compromise — see Coverage & confidence.
03
Why it matters
— the attack path, told twice: adversary, then board1
Front door — unauthenticated access narrative 1
Attacker
I craft a malicious input to trigger a heap buffer overflow in the WinSock auxiliary driver.
Business
An attacker gains a foothold on the system through local access or a prior compromise.
2
Keys to the kingdom — privilege/identity takeover narrative 2
Attacker
I exploit the overflow to corrupt heap memory and hijack execution flow within kernel context.
Business
The attacker bypasses security boundaries designed to isolate user and kernel privilege levels.
3
Lateral reach — past segmentation narrative 3
Attacker
I achieve SYSTEM-level code execution and maintain persistent control over the compromised host.
Business
The organization loses administrative control of affected endpoints and faces data exfiltration, malware deployment, and lateral movement risks.
04
What to do
— defensible action- Remediate per the vendor advisory — confirm the fixed build for your version and verify exposure.1
Say it to the boardA vulnerability with this evidence profile is a defensible budget line, not a backlog ticket — fund the change against the proof above.
05