Security readout for executives and security teams
Plain-English summary
This is a Microsoft Windows privilege-escalation flaw in the Ancillary Function Driver for WinSock. An attacker who already has low-privileged local access could gain higher privileges. CISA lists it in KEV, so exploited-in-the-wild activity is supported by a government source.
Executive priority
Treat as urgent patching work because CISA KEV confirms real-world exploitation. It is mainly a post-compromise privilege escalation, but that can convert a limited breach into full host control on important Windows assets.
Technical view
CVE-2025-21418 is a CWE-122 heap-based buffer overflow in Windows Ancillary Function Driver for WinSock. CVSS is 7.8: local attack vector, low complexity, low privileges required, no user interaction, and high confidentiality, integrity, and availability impact. Microsoft marks remediation as official.
Likely exposure
Organizations running affected Windows 10, Windows 11, and Windows Server versions listed in the source bundle may be exposed if systems are unpatched. This is most relevant on endpoints, RDS hosts, servers with local users, and systems where malware could already execute locally.
Exploitation context
Active exploitation is supported by CISA KEV. The vulnerability is not described as remote initial access; it requires local low-privileged access. Business risk is greatest when chained after phishing, malware execution, stolen credentials, or other footholds.
Researcher notes
Public sources confirm KEV status, CVSS 7.8, CWE-122, and affected Windows client/server products. The provided bundle does not include exploit mechanics or detailed indicators. Avoid assumptions about exploit maturity beyond CISA KEV and Microsoft’s official remediation status.
Mitigation direction
- Apply Microsoft security updates for CVE-2025-21418 across affected Windows systems.
- Use MSRC guidance for product-specific patches, supersedence, and servicing requirements.
- Prioritize KEV-covered assets, privileged workstations, servers, and shared Windows hosts.
- Accelerate remediation where endpoint telemetry shows suspicious local execution.
- Track CISA KEV status and internal patch exceptions until closed.
Validation and detection
- Inventory Windows versions against the affected product list in MSRC and the source bundle.
- Confirm installed Microsoft updates remediate CVE-2025-21418 for each OS build.
- Validate patch compliance through endpoint management or vulnerability scanning reports.
- Review EDR alerts for post-compromise privilege-escalation behavior on unpatched hosts.
- Document remaining exceptions with owner, business reason, and remediation date.
Public sources used
Generated from the cited source records. This long-tail analysis has not been individually reviewed by a named human.
Conservative CVE-to-ATT&CK context
These mappings and lookup hints may be relevant to the vulnerability behavior, CWE, affected product, or exposure path. Glexia-inferred context is not an official MITRE, ATT&CK, CWE, or CVE Program mapping.
ATT&CK lookup starting points
Use these exact CWE pages and searches to review the Glexia ATT&CK library from this CVE's weakness and description context.
CWE-122: Exact CWE lookup
Use the exact CWE identifier as the starting point before reviewing related ATT&CK behavior. Open the exact CWE lookup page first, then review the ATT&CK searches from that MITRE weakness context. This is a Glexia lookup hint, not an official ATT&CK mapping.
Open ATT&CK lookupPrivilege behavior lookup
The CVE wording references privilege impact, so privilege escalation and authorization behavior review may help. This is a Glexia inferred lookup path, not an official MITRE, ATT&CK, or CVE Program mapping.
Open ATT&CK lookupCVE-2025-21418 mapping review
Open the CVE-to-ATT&CK bridge for reviewed, inferred, or future official mappings tied to this CVE.
Open ATT&CK lookup- Severity
- High
- CVSS
- 7.8 (3.1)
- Known Exploited
- Yes
- Published
Vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C
CNA and ADP enrichment extracted from CVE v5
These fields come from the CVE record and ADP containers, not from Glexia's Take. They preserve time-varying source decisions such as CISA SSVC, KEV status, CVSS metrics, and provider references.
CISA KEV status
CVSS vector scores
1 official scoreWe collect every scored CVSS vector available in the official CNA and ADP containers. When more than one version is present, the table keeps the source vectors side by side instead of collapsing them into the highest score.
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C1.85.9Primary CVE scoreVulnerability scoring details
Base CVSS 3.1 score
7.8HighVector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:F/RL:O/RC:C
Source materials
- CVE List V5 sourceCVE List V5
- Windows Ancillary Function Driver for WinSock Elevation of Privilege VulnerabilityCVE reference · vendor-advisory, patch
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-21418CVE reference · government-resource
Products and packages named in the record
CWE details
CWE links open Glexia weakness intelligence pages with official CWE context, developer remediation guidance, and related CVE mappings.
Heap-based Buffer Overflow
Heap-based Buffer Overflow represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.