Historical catalog analysis: CISA added this entry on February 11, 2025. The entry reflects catalog information retrieved on August 31, 2026, not a snapshot archived on the inclusion date. Check current vendor guidance before acting.
What the vulnerability is
CVE-2025-21418 is a heap-based buffer overflow (CWE-122) located within the Microsoft Windows Ancillary Function Driver for WinSock. This flaw enables a local attacker—one who already has an established presence on the system—to escalate their privileges to the SYSTEM level, the highest privilege tier in the Windows environment.
Exposure and applicability
This vulnerability affects systems running the Windows Ancillary Function Driver for WinSock. Because this is a local privilege escalation (LPE) flaw, the exposure path requires the attacker to have existing local access to the target machine. The risk is most acute on shared workstations or servers where multiple users or low-privileged service accounts operate, as these provide the necessary initial foothold to attempt the overflow.
Remediation priorities
Based on the inclusion of this vulnerability in CISA’s Known Exploited Vulnerabilities (KEV) catalog on February 11, 2025, remediation should be prioritized for assets that are exposed to multiple local users or high-risk service accounts.
Our analysis suggests the following priority sequence:
1. Immediate Patching: Apply vendor-supplied mitigations as specified by Microsoft. For federal agencies, CISA has established a remediation deadline of March 4, 2025.
2. Asset Decommissioning: If vendor mitigations are unavailable or cannot be applied to legacy systems, the product should be discontinued to remove the attack surface.
3. Privilege Review: Audit local accounts and service permissions to reduce the number of entities capable of interacting with the affected driver.
How to validate remediation
Verification must move beyond a simple version check of the OS build. To ensure exposure is reduced, vulnerability management teams should:
* Verify Driver State: Confirm that the specific Ancillary Function Driver for WinSock has been updated to the patched version or disabled if no longer required.
* Configuration Audit: Ensure that system-wide security updates have been successfully applied and that the driver is not being overridden by older, vulnerable versions in custom images.
Confirmation of a patch installation does not guarantee immunity if the driver remains active in an unpatched state due to pending reboots or configuration conflicts.
Limits and open questions
It remains unknown whether this vulnerability has been utilized in ransomware campaigns. Additionally, while the impact is clear (SYSTEM privileges), the specific conditions required to trigger the heap overflow—such as specific API calls or memory states—are not detailed in the source. Residual risk persists if attackers utilize other undiscovered LPE vectors to bypass the updated driver.
Source and editorial note
CVE-2025-21418: Microsoft Windows Ancillary Function Driver for WinSock Heap-Based Buffer Overflow Vulnerability · Source date: February 11, 2025 · Retrieved August 31, 2026.
Material facts are tied to the cited primary source. Recommendations are independent defensive analysis unless attributed to the source. Confirm consequential decisions against current authoritative guidance.
Archive date: February 14, 2025. The displayed post date is assigned three days after the source date to organize this retrospective archive; it does not mean this site published the analysis then. First published by this site: October 25, 2026 at 00:26 UTC.
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