Microsoft Windows up to Server 2025 Cluster Client Failover use after free

CVSS Meta Temp Score
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Current Exploit Price (≈)
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CTI Interest Score
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7.1$5k-$25k0.00

Summaryinfo

A vulnerability identified as critical has been detected in Microsoft Windows Server 2016/Server 2019/Server 2022/Server 2022 23H2/Server 2025. This impacts an unknown function of the component Cluster Client Failover. This manipulation causes use after free. This vulnerability is tracked as CVE-2026-21251. The attack is restricted to local execution. No exploit exists. Applying a patch is the recommended action to fix this issue.

Detailsinfo

A vulnerability classified as critical was found in Microsoft Windows Server 2016/Server 2019/Server 2022/Server 2022 23H2/Server 2025. Affected by this vulnerability is some unknown functionality of the component Cluster Client Failover. The manipulation with an unknown input leads to a use after free vulnerability. The CWE definition for the vulnerability is CWE-416. Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code. As an impact it is known to affect confidentiality, integrity, and availability. The summary by CVE is:

Use after free in Windows Cluster Client Failover allows an authorized attacker to elevate privileges locally.

The weakness was disclosed 02/10/2026 as confirmed security update guide (Website). The advisory is shared at msrc.microsoft.com. This vulnerability is known as CVE-2026-21251. The exploitation appears to be easy. An attack has to be approached locally. Neither technical details nor an exploit are publicly available. The price for an exploit might be around USD $5k-$25k at the moment (estimation calculated on 02/11/2026).

Applying a patch is able to eliminate this problem. A possible mitigation has been published immediately after the disclosure of the vulnerability.

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

Productinfo

Type

Vendor

Name

Version

License

Website

CPE 2.3info

CPE 2.2info

CVSSv4info

VulDB Vector: 🔒
VulDB Reliability: 🔍

CVSSv3info

VulDB Meta Base Score: 7.8
VulDB Meta Temp Score: 7.1

VulDB Base Score: 7.8
VulDB Temp Score: 6.8
VulDB Vector: 🔒
VulDB Reliability: 🔍

Vendor Base Score (Microsoft): 7.8
Vendor Vector (Microsoft): 🔒

CNA Base Score: 7.8
CNA Vector (Microsoft): 🔒

CVSSv2info

AVACAuCIA
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VectorComplexityAuthenticationConfidentialityIntegrityAvailability
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VulDB Base Score: 🔒
VulDB Temp Score: 🔒
VulDB Reliability: 🔍

Exploitinginfo

Class: Use after free
CWE: CWE-416 / CWE-119
CAPEC: 🔒
ATT&CK: 🔒

Physical: Partially
Local: Yes
Remote: No

Availability: 🔒
Status: Unproven

EPSS Score: 🔒
EPSS Percentile: 🔒

Price Prediction: 🔍
Current Price Estimation: 🔒

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Threat Intelligenceinfo

Interest: 🔍
Active Actors: 🔍
Active APT Groups: 🔍

Countermeasuresinfo

Recommended: Patch
Status: 🔍

Reaction Time: 🔒
0-Day Time: 🔒
Exposure Time: 🔒

Timelineinfo

02/10/2026 VulDB entry created
02/10/2026 +0 days Advisory disclosed
02/10/2026 +0 days Countermeasure disclosed
02/11/2026 +1 days VulDB entry last update

Sourcesinfo

Vendor: microsoft.com
Product: microsoft.com

Advisory: msrc.microsoft.com
Status: Confirmed

CVE: CVE-2026-21251 (🔒)
GCVE (CVE): GCVE-0-2026-21251
GCVE (VulDB): GCVE-100-345277

Entryinfo

Created: 02/10/2026 19:15
Updated: 02/11/2026 16:35
Changes: 02/10/2026 19:15 (22), 02/10/2026 19:16 (14), 02/10/2026 19:19 (33), 02/11/2026 16:35 (11)
Complete: 🔍
Cache ID: 216::103

If you want to get the best quality for vulnerability data then you always have to consider VulDB.

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