Security readout for executives and security teams
Plain-English summary
This is a Windows Hyper-V related local privilege escalation flaw. An attacker who already has low-level local access could potentially gain powerful system-level control, affecting confidentiality, integrity, and availability. CISA lists it in KEV, so treat it as actively exploited and prioritize patching exposed Windows fleets.
Executive priority
Patch on an accelerated timeline. This is a high-impact privilege escalation with active exploitation evidence from CISA KEV, but it requires local access. Treat it as urgent fleet hygiene, especially on shared systems and servers.
Technical view
CVE-2025-21335 is a CWE-416 use-after-free in Windows Hyper-V NT Kernel Integration VSP. Microsoft rates it high with CVSS 3.1 score 7.8: local attack vector, low complexity, low privileges required, no user interaction, and high impact across CIA. Microsoft lists official remediation availability.
Likely exposure
Exposure is limited to affected Microsoft Windows versions listed in the bundle, including Windows 10, Windows 11, Windows Server 2022 23H2 Server Core, and Windows Server 2025. The risk is highest on systems where low-privileged local users or local code execution are plausible.
Exploitation context
CISA KEV inclusion supports active exploitation. The source bundle does not provide exploit mechanics, campaign details, or affected configurations beyond Microsoft’s product list. This is not described as remotely exploitable; the CVSS vector indicates local access and low privileges are required.
Researcher notes
The bundle supports use-after-free, local privilege escalation, affected Microsoft OS versions, CVSS 7.8, vendor remediation, and KEV status. It does not include root-cause detail, proof-of-concept status, exploit chains, indicators, or configuration prerequisites beyond the affected products.
Mitigation direction
- Apply Microsoft security updates from the CVE-2025-21335 advisory.
- Prioritize assets matching the affected Windows and Windows Server versions.
- Track CISA KEV remediation expectations for governed environments.
- Review Microsoft guidance for any version-specific servicing requirements.
- Reduce unnecessary local user access on unpatched systems.
Validation and detection
- Inventory Windows builds against Microsoft’s affected product list.
- Confirm January 2025 or later applicable Microsoft security updates are installed.
- Check vulnerability management tools for CVE-2025-21335 closure.
- Review CISA KEV status during remediation tracking.
- Prioritize validation on multi-user endpoints, servers, and virtualization-related systems.
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-2025-21335 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: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.
CISA KEV status
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:L/PR:L/UI:N/S:U/C:H/I:H/A:H/E:U/RL:O/RC:C1.85.9microsoftVulnerability 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: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.
- Added to KEVCISA-ADP
CISA Known Exploited Vulnerabilities metadata lists this CVE as known exploited.
- ADP timelineCISA-ADP
CVE-2025-21335 added to CISA KEV
- 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
- 2025-01-14T00:00:00.000Z: CVE-2025-21335 added to CISA KEV
Source materials
- CVE List V5 sourceCVE List V5
- Windows Hyper-V NT Kernel Integration VSP Elevation of Privilege VulnerabilityCVE reference, microsoft · vendor-advisory, patch
- https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-21335CVE reference, CISA-ADP · 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.
Use After Free
Use After Free represents a recurring weakness pattern that can create exploitable paths when design, validation, or implementation controls are missing.