What is the CVSS score of CVE-2025-21335?

CVE-2025-21335 has a CVSS 3.1 base score of 7.8 (High). CVSS vector: CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H. EPSS exploitation probability: 8.7%.

Is CVE-2025-21335 being actively exploited?

Yes, CVE-2025-21335 is listed in the CISA Known Exploited Vulnerabilities (KEV) catalog, confirming active in-the-wild exploitation. Immediate patching is required.

How to fix or mitigate CVE-2025-21335?

Within 24 hours: Identify all affected systems and apply vendor patches immediately. If patching is delayed, consider network segmentation to limit exposure.

Windows 10 21h2 CVE-2025-21335

HIGH

Use After Free (CWE-416)

2025-01-14 secure@microsoft.com

Information Disclosure Use After Free Memory Corruption Microsoft Windows 10 21h2 Windows 10 22h2 Windows 11 22h2 Windows 11 23h2 Windows 11 24h2 Windows Server 2022 23h2 Windows Server 2025

7.8

CVSS 3.1 · Vendor: microsoft

View

Vulnerability Assessment

Weakness	CWE CWE-416 OWASP Top 10:2025 A06:2021 - Vulnerable and Outdated Components ASVS 5.0 V15 - Secure Coding and Architecture Memory lifecycle management MITRE ATT&CK 2 techniques across 2 tactics: Execution, Privilege Escalation The technique list with ATT&CK links and the kill-chain view is part of the Basic plan and up. Sign in to read
Impact	High risk (CVSS 7.8). Three independent vulnerabilities in the same component suggest the attacker had deep knowledge of Hyper-V internals.
Exploit ScenarioDerived	Used as a backup exploitation path when the other two Hyper-V vulnerabilities fail due to heap layout variations, ensuring reliable privilege escalation.

Act Now Prioritize within 24-48h. Why: In CISA KEV with patch available.

Exploited in the wild (CISA KEV) Patch available 8.7% exploitation probability (EPSS)

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AnalysisAIv1 – Mar 28, 2026

Windows Hyper-V NT Kernel Integration VSP contains a use-after-free vulnerability for local privilege escalation, the third of three Hyper-V zero-days exploited in January 2025.

Earlier versions of this analysis (1)

v1 Mar 28, 2026 - 18:03 CVSS 7.8

The third use-after-free in Hyper-V VSP completing the January 2025 triple zero-day set, enabling local privilege escalation through kernel memory corruption.

RemediationAI

Apply January 2025 security updates for all three Hyper-V CVEs.

Affects your stack

Find out whether the stacks and servers you run are on an affected version.

Checking this CVE against your own stacks and servers is part of the Basic plan and up.

Technical ContextAI · show details

The CWE-416 use-after-free provides a third exploitation path through the Hyper-V VSP, reinforcing the systematic nature of the attack against Hyper-V's kernel integration layer.

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Exploit and PoC references, threat intelligence from 22 sources

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Severity by source

Vendor (microsoft) PRIMARY 7.8 HIGH

AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H

Primary rating from Vendor (microsoft) · only source for this CVE.

CVSS VectorVendor: microsoft

Attack Vector

Local

Attack Complexity

Low

Privileges Required

Low

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Lifecycle Timeline

Patch released

Mar 28, 2026 - 18:03 nvd

Patch available

Added to CISA KEV

Oct 27, 2025 - 17:13 cisa

CISA KEV

CVE Published

Jan 14, 2025 - 18:15 nvd

HIGH 7.8

DescriptionCVE.org

Windows Hyper-V NT Kernel Integration VSP Elevation of Privilege Vulnerability

Executive ViewAI

Why It Matters

CVE-2025-21335 presents notable security risk, a use-after-free vulnerability rated CVSS 7.8. Exploitation could compromise the security of affected deployments. This vulnerability is actively exploited in the wild (KEV-listed) and requires immediate remediation. A patch is available and should be applied as part of regular vulnerability management.

Business Impact: Severe

Compensating Controls

Apply vendor patch. If immediate patching is not feasible: (1) Enable ASLR and DEP where available; (2) Implement network segmentation; (3) Monitor for exploitation indicators.

Threat Intelligence Overview

EPSS Score

8.7%

Top 8% exploitable

Data Quality

4 sources

Confidence: Medium

NVD

CVE.org

CISA KEV

EPSS CERT-EU

How this decision was reached

The engine reads each signal below and applies a fixed list of rules from top to bottom. The first rule that matches sets the recommended action – like a statement, every line is shown.

SignalValue

Severity HIGH

CISA KEV Yes

Public POC No

EPSS 8.7%

Patch available Yes

Active threat Yes

Deciding rule

In CISA KEV with patch available

What every action level means

Emergency Immediate action required. Criteria: CRITICAL + in CISA KEV (actively exploited) without patch, OR CRITICAL + EPSS > 30% without patch, OR CRITICAL + active threat signals without patch.

Act Now Prioritize within 24-48h. Criteria: in KEV with patch available, OR CRITICAL + public POC, OR HIGH + EPSS > 10%, OR CRITICAL + active threat, OR any CRITICAL severity.

This Week Schedule remediation this week. Criteria: HIGH severity (CVSS 7.0-8.9). Patch within normal change window.

This Month Plan within 30 days. Criteria: MEDIUM severity (CVSS 4.0-6.9), lower exploitation probability. Include in regular patch cycle.

Monitor Track and reassess. Criteria: LOW severity (CVSS 0.1-3.9), minimal exploitation risk. No immediate action needed.

SSVC AssessmentENISA

SSVC Decision· derived

Out-of-Cycle

Exploitation· derived

Active

System Exposure· derived

Small

Automatable· derived

Human Impact

Very High

Priority Score

Low Medium High Critical

KEV: +50

EPSS: +9

CVSS: +39

PoC: 0

Weaponized: 0

Threat intel: 0

Gov advisory: 0

Attack Technique

Use After Free HIGH

Use-after-free vulnerabilities occur when a program continues to access memory through a pointer after that memory has been deallocated.

Memory Corruption HIGH

Memory corruption occurs when a program writes data beyond the boundaries of allocated memory regions or accesses memory in unintended ways, violating the integrity of the process's address space.

Information Disclosure MEDIUM

Information disclosure occurs when an application unintentionally exposes sensitive data that aids attackers in reconnaissance or directly compromises security.

Affected Products (CPE)CVE.org

cpe:2.3:o:microsoft:windows_10_21h2:*:*:*:*:*:*:x64:*

cpe:2.3:o:microsoft:windows_10_22h2:*:*:*:*:*:*:x64:*

cpe:2.3:o:microsoft:windows_11_22h2:*:*:*:*:*:*:arm64:*

cpe:2.3:o:microsoft:windows_11_22h2:*:*:*:*:*:*:x64:*

cpe:2.3:o:microsoft:windows_11_23h2:*:*:*:*:*:*:arm64:*

cpe:2.3:o:microsoft:windows_11_23h2:*:*:*:*:*:*:x64:*

cpe:2.3:o:microsoft:windows_11_24h2:*:*:*:*:*:*:arm64:*

cpe:2.3:o:microsoft:windows_11_24h2:*:*:*:*:*:*:x64:*

cpe:2.3:o:microsoft:windows_server_2022_23h2:*:*:*:*:*:*:*:*

cpe:2.3:o:microsoft:windows_server_2025:*:*:*:*:*:*:*:*

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References

Advisories & patches

PATCH https://msrc.microsoft.com/update-guide/vulnerability/CVE-2025-21335 REF https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-21335

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