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PatchSiren cyber security CVE debrief

CVE-2025-21418 Microsoft CVE debrief

CVE-2025-21418 is a Microsoft Windows vulnerability in the Ancillary Function Driver for WinSock described as a heap-based buffer overflow. CISA added it to the Known Exploited Vulnerabilities catalog on 2025-02-11, which means defenders should treat it as an actively relevant remediation item rather than a routine advisory. The CISA record directs organizations to apply vendor mitigations or discontinue use of the product if mitigations are unavailable.

Vendor
Microsoft
Product
Windows
CVSS
HIGH 7.8
CISA KEV
Listed
Original CVE published
2025-02-11
Original CVE updated
2025-02-11
Advisory published
2025-02-11
Advisory updated
2025-02-11

Who should care

Windows administrators, vulnerability management teams, endpoint security teams, and SOC/incident response staff responsible for Microsoft Windows fleets should prioritize this CVE. It is especially important for organizations that track CISA KEV items against patch SLAs and remediation deadlines.

Technical summary

The supplied record describes a heap-based buffer overflow affecting the Windows Ancillary Function Driver for WinSock. Beyond that title-level classification, the provided corpus does not include affected versions, attack prerequisites, exploit details, or confirmed impact.

Defensive priority

High

Recommended defensive actions

  • Review the Microsoft update guidance referenced by CISA for CVE-2025-21418 and deploy the relevant security update(s) to affected Windows systems.
  • Treat this as a KEV-driven remediation item and confirm patch completion before the CISA due date of 2025-03-04.
  • If vendor mitigation is unavailable for a specific deployment, follow vendor/CISA guidance and remove or discontinue use of the affected product or configuration until remediation is possible.
  • Validate coverage with asset inventory and vulnerability management reporting so all Windows endpoints are included in the remediation effort.

Evidence notes

CISA's Known Exploited Vulnerabilities catalog lists CVE-2025-21418 as a Microsoft Windows issue with dateAdded 2025-02-11 and dueDate 2025-03-04. The supplied CISA metadata also references the Microsoft MSRC update guide for CVE-2025-21418 and the NVD entry as supporting official references. The CVE and source timestamps supplied in the corpus are both 2025-02-11.

Sources and references

Verified primary and authoritative sources

  • CVE-2025-21418 CVE Program record

    Publisher, destination, and source semantics verified

    URL: https://www.cve.org/CVERecord?id=CVE-2025-21418

    CVE Program - Official CVE Program record with source-provided CVE metadata.

  • CVE-2025-21418 NVD vulnerability detail

    Publisher, destination, and source semantics verified

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

    NIST National Vulnerability Database - Official NIST NVD detail page and source-specific vulnerability assessment.

  • CISA Known Exploited Vulnerabilities catalog

    Publisher, destination, and source semantics verified

    URL: https://www.cisa.gov/known-exploited-vulnerabilities-catalog

    Cybersecurity and Infrastructure Security Agency - Official CISA catalog of vulnerabilities known to be exploited in the wild.

Supplemental references

  • Source item URL

    Unverified legacy reference

    URL: https://www.cisa.gov/sites/default/files/feeds/known_exploited_vulnerabilities.json

    cisa_kev

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.