Security readout for executives and security teams
Plain-English summary
This is a Windows local privilege escalation flaw in the Ancillary Function Driver for WinSock. An attacker who already has low-level access to a vulnerable Windows system could potentially gain higher privileges. It is not described as remotely exploitable by itself, but it can increase the impact of malware, insider activity, or a compromised account.
Executive priority
Treat as a high-priority patching item, especially for servers and systems with multiple local users. It is not currently evidenced as actively exploited in the provided sources, but it can turn a limited compromise into full system control.
Technical view
CVE-2026-21241 is a CWE-416 use-after-free in the Windows Ancillary Function Driver for WinSock. Microsoft rates it high severity with CVSS 7.0. The vector is local, high attack complexity, low privileges required, no user interaction, unchanged scope, and high confidentiality, integrity, and availability impact. Microsoft lists remediation as available.
Likely exposure
Exposure is limited to listed Windows 11 and Windows Server versions, including Windows 11 22H3 through 26H1, Windows Server 2022, Server 2022 23H2 Server Core, and Windows Server 2025 including Server Core. Systems are at higher business risk where untrusted users, shared workstations, or compromised accounts exist.
Exploitation context
The source bundle does not show CISA KEV listing or active exploitation. Microsoft’s CVSS data marks exploit code maturity as unproven. Exploitation requires local access and low privileges, so this is most relevant as a post-compromise privilege escalation path rather than an initial entry vector.
Researcher notes
Analysis is limited to the supplied CVE and MSRC data. No public exploit details, exploit steps, or independent technical write-up were provided. Key constraints are local attack vector, high complexity, low privileges required, and use-after-free in the Windows AFD WinSock component.
Mitigation direction
- Apply the Microsoft security update referenced in the MSRC advisory.
- Prioritize shared systems, servers, developer workstations, and internet-facing support infrastructure.
- Restrict unnecessary local user access on affected Windows systems.
- Monitor Microsoft guidance for any revised affected versions or mitigations.
Validation and detection
- Inventory Windows builds against the affected versions in the MSRC advisory.
- Confirm the relevant Microsoft security update is installed.
- Review endpoint detections for suspicious local privilege escalation behavior.
- Check whether vulnerable Server Core deployments are included in patch coverage.
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-416: 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-2026-21241 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 (3.1)
- Known Exploited
- No
- Published
Vector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/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.
SSVC decision data
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:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C15.9microsoftVulnerability scoring details
Base CVSS 3.1 score
7HighVector: CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C
Vulnerability timeline
Timeline events are normalized from CVE metadata, CNA source timelines, ADP timelines, and KEV metadata when present.
- CVE reservedCVE Program
The CVE ID was reserved by the assigning CNA.
- CVE publishedCVE Program
The CVE record was published.
- CVE updatedCVE Program
The CVE record metadata indicates this as the latest update time.
ADP provider summaries
Source materials
- CVE List V5 sourceCVE List V5
- Windows Ancillary Function Driver for WinSock Elevation of Privilege VulnerabilityCVE reference, microsoft · vendor-advisory, patch
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.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.