Security readout for executives and security teams
Plain-English summary
A memory-safety flaw in a Windows networking driver could let a user who already has local, low-privileged access gain higher privileges. Successful exploitation could compromise confidentiality, integrity, and availability. It is not described as remotely exploitable by itself.
Executive priority
Treat this as a high-priority privilege-escalation update, especially on multi-user endpoints and servers where local access is broadly available. It does not appear to provide initial remote entry, but it could amplify another compromise. Patch through normal expedited Windows maintenance after compatibility validation.
Technical view
CVE-2026-21241 is a use-after-free vulnerability (CWE-416) in the Windows Ancillary Function Driver for WinSock. The CVSS 3.1 score is 7.0: local access, low privileges, high attack complexity, and no user interaction are required, with potentially high impact across confidentiality, integrity, and availability.
Likely exposure
Exposure applies to the listed Windows 11 releases and Windows Server 2022/2025 editions, including specified Server Core installations. Organizations should compare deployed releases and build baselines against Microsoft’s advisory. The bundle contains duplicate and potentially inconsistent product naming, so Microsoft’s current applicability data should be authoritative.
Exploitation context
The attacker must already have authorized local access with low privileges, and exploitation is assessed as high complexity. The bundle does not show CISA KEV inclusion and provides no cited evidence of active exploitation or public exploit availability. Absence from KEV does not prove the vulnerability is not being exploited.
Researcher notes
The vulnerability is classified as CWE-416 in the WinSock ancillary function driver. The supplied vector indicates AV:L/AC:H/PR:L/UI:N/S:U with high C/I/A impact. Exact vulnerable ranges, fixed builds, KB identifiers, technical trigger details, and exploitation telemetry are absent from the bundle; verify these directly with MSRC.
Mitigation direction
- Apply the applicable Microsoft security update according to the MSRC advisory.
- Consult MSRC for exact KB numbers, fixed builds, prerequisites, and restart requirements.
- Prioritize shared workstations, servers, and systems where low-privileged users can obtain local access.
- Limit unnecessary local accounts and interactive access while patch deployment is pending.
Validation and detection
- Inventory systems matching the listed Windows releases, editions, and build baselines.
- Confirm each system has the applicable MSRC-listed update or fixed build installed.
- Check deployment tooling for failed, pending, or rolled-back updates.
- Reassess exposure after Microsoft clarifies any inconsistent product naming in the affected list.
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.