Microsoft — Microsoft Windows Ancillary Function Driver for WinSock Heap-Based Buffer Overflow Vulnerability
CISA KEV · in the CISA KEV catalog since 2025-02-11
Listed in the CISA KEV catalog, and an EPSS probability of 0.016.
Patch This Cycle
The priority band answers “how soon”, not “how bad” — see Methodology for what it weighs and where it abstains.
| Measure | Value | Source | What it means |
|---|---|---|---|
| CVSS base score | 7.8 | NVD | How severe the flaw is in itself. It does not say how likely an attack is. |
| FIRST EPSS | 0.016 (74.9th pctl) | FIRST | FIRST's estimate of the chance this is exploited in the next 30 days, and how that ranks against all CVEs. |
| Actively exploited | Confirmed | CISA KEV | Whether a source of record has confirmed attacks using it in the wild. |
| Ransomware campaign use | Unknown or none | CISA KEV | Whether CISA has seen ransomware operators use it. |
| CISA remediation deadline | 2025-03-04 — KEV since 2025 · listed over a year | CISA KEV | The date US federal agencies must have fixed or mitigated it. |
| Fixed in | windows 10 1607: update to 10.0.10240.20915 or later | windows 10 1809: update to 10.0.17763.6893 or later | windows 10 21h2: update to 10.0.19044.5487 or later | windows 10 22h2: update to 10.0.19045.5487 or later | windows 11 22h2: update to 10.0.22621.4890 or later | windows 11 23h2: update to 10.0.22631.4890 or later | NVD | The version(s) the vendor has published as fixed, where NVD records one. |
| Public exploit module | None known | Metasploit | Module existing is not the same as active exploitation. |
| EUVD cross-reference | Listed | ENISA EUVD | ENISA's own vulnerability database entry for this CVE, where one exists. |
Impacted software or hardware
+6 more affected products — see the full list at NVD.
Fixed versions: windows 10 1607: update to 10.0.10240.20915 or later | windows 10 1809: update to 10.0.17763.6893 or later | windows 10 21h2: update to 10.0.19044.5487 or later | windows 10 22h2: update to 10.0.19045.5487 or later | windows 11 22h2: update to 10.0.22621.4890 or later | windows 11 23h2: update to 10.0.22631.4890 or later
Remediation: Apply mitigations per vendor instructions or discontinue use of the product if mitigations are unavailable.
Remediation basis: CISA KEV required action
ENISA EUVD also lists this CVE at CVSS 7.8 (v3.1), assigned by microsoft. Source: euvd.enisa.europa.eu.
This page is an opinion about urgency. Where it and a source of record disagree, the source of record is the record.
Where this sits
CVE-2025-21418 is a Microsoft entry in the CISA KEV catalog. The priority feed ranks Microsoft's current monthly release rather than older Microsoft CVEs, so this one is not listed there; the page above scores it from the same sources.
