Security readout for executives and security teams
Plain-English summary
A user who already has local access to an affected Windows system may exploit a timing flaw in the Local Security Authority to gain higher privileges. Successful exploitation could expose sensitive data, permit system changes, or disrupt the device. The attack requires local access and precise timing, reducing—but not removing—the risk.
Executive priority
Treat as a high-priority patching item, especially on systems where an initial foothold could lead to administrative control. It is not described as remotely exploitable or actively exploited, so response should be risk-based rather than emergency-wide. Track remediation to completion and escalate exceptions involving sensitive or privileged systems.
Technical view
CVE-2025-21191 is a CWE-367 time-of-check/time-of-use race condition in Windows LSA. It requires local access, low privileges, no user interaction, and high attack complexity. Successful exploitation can elevate privileges with high confidentiality, integrity, and availability impact. The supplied CVSS v3.1 score is 7.0.
Likely exposure
Exposure exists where the listed Windows 10, Windows 11, or Windows Server releases remain without Microsoft's applicable security update. Prioritize shared endpoints, administrative workstations, servers, and systems where untrusted or compromised users can execute locally. The supplied affected list may not establish every vulnerable build or servicing state.
Exploitation context
The bundle identifies local privilege escalation rather than remote compromise. An attacker must already be authorized with low privileges and win a race condition, reflected by high attack complexity. KEV is false, and the supplied sources provide no evidence of active exploitation. This does not prove exploitation is absent outside the bundle.
Researcher notes
Assessment is limited to the supplied public bundle. It names CWE-367 and provides the CVSS vector, affected releases, and a Microsoft patch reference, but no vulnerable code path, fixed build numbers, KB identifiers, indicators of compromise, or exploitation telemetry. Validate exact applicability and update supersedence through Microsoft's advisory.
Mitigation direction
- Apply the applicable Microsoft security update identified in the vendor advisory.
- Prioritize exposed servers, privileged workstations, and multi-user Windows systems.
- Restrict unnecessary local access and software execution while remediation is pending.
- Check Microsoft guidance for product-specific servicing and restart requirements.
Validation and detection
- Inventory affected Windows editions, versions, builds, and servicing status.
- Compare installed updates with Microsoft's CVE advisory for each operating system.
- Confirm deployment completion and required restarts across managed endpoints.
- Re-scan systems after remediation and investigate hosts that remain outdated.
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-367: 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-2025-21191 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 Local Security Authority (LSA) 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.
Time-of-check Time-of-use (TOCTOU) Race Condition
Time-of-check Time-of-use (TOCTOU) Race Condition represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.