VulnerabilityAnalyzed

CVE-2026-21510

Microsoft Windows Shell Protection Mechanism Failure Vulnerability

KEVHIGH 8.8EPSS 26.2%

Does this matter?

Known to be exploited in the wild (CISA KEV, CISA remediation deadline 3 March 2026). Treat as an emergency change: patch or isolate now, then hunt for prior compromise.

Description

Protection mechanism failure in Windows Shell allows an unauthorized attacker to bypass a security feature over a network.

CVSS 3.1: 8.8 HIGHCVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:U/C:H/I:H/A:H
EPSS: 26.24% probability · 98th percentile
CISA KEV: Listed 10 February 2026 · due 3 March 2026
Weakness: CWE-693
Affected: microsoft/windows 10 1607 · microsoft/windows 10 1809 · microsoft/windows 10 21h2 · microsoft/windows 10 22h2 · microsoft/windows 11 23h2 · microsoft/windows 11 24h2 · microsoft/windows 11 25h2 · microsoft/windows server 2012 · microsoft/windows server 2016 · microsoft/windows server 2019 · microsoft/windows server 2022 · microsoft/windows server 2022 23h2 · microsoft/windows server 2025
Source: secure@microsoft.com

CISA notes

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21510 ; https://nvd.nist.gov/vuln/detail/CVE-2026-21510

References

https://msrc.microsoft.com/update-guide/vulnerability/CVE-2026-21510Vendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2026-21510US Government Resource

Source: NVD record, EPSS from FIRST.org, KEV from CISA. Refreshed daily.