Vulnerability intelligence

CVE-2026-21510

Microsoft Windows Shell Protection Mechanism Failure Vulnerability

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

CVSS Score

8.8

High

EPSS — Exploit Probability

26%

Riskier than 98% of all CVEs

Exploitation

Confirmed in the wild

Used in ransomware campaigns

Remediation

Patch available

Federal deadline 2026-03-03

CISA required action

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable. Deadline for federal agencies: 2026-03-03.

NVD entry Vendor patch PoC / advisory CISA KEV

3 articles across 2 outlets · first covered Apr 27, 2026 · latest Apr 29, 2026

Tracked incidents

vulnerability closed 4 articles

CISA adds Windows Shell and ConnectWise ScreenConnect flaws to Known Exploited Vulnerabilities catalog

Associated threat actors

APT28

Coverage timeline

CISA Flags Actively Exploited CVE-2024-1708 and Windows Flaw
thehackernews.com · Apr 29, 2026
Microsoft Warns of Active Exploit in CVE-2026-32202 Spoof Flaw
thehackernews.com · Apr 28, 2026
APT28 exploits Windows SmartScreen gap for zero click LNK attacks
www.securityweek.com · Apr 27, 2026

Related CVEs — Microsoft

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