CVE-2026-21510

Microsoft Windows Shell contains a protection mechanism failure (CWE-693) that allows an unauthorized attacker to bypass a security feature, which CISA notes can be reached over a network. Successful exploitation defeats a Windows defense-in-depth control, weakening protections an attacker would otherwise have to evade as part of a broader intrusion; the available data does not describe a code-execution or privilege-escalation gain. Any system running Microsoft Windows falls within CISA's published affected scope, and specific version ranges have not been enumerated in the available data. The flaw was added to CISA's Known Exploited Vulnerabilities catalog on 2026-02-10, confirming exploitation in the wild, and its EPSS score of 26.2% (98th percentile) signals elevated near-term exploitation risk; ransomware use is unknown and no public proof-of-concept is known.

What to do: Apply Microsoft's applicable Windows security update through Windows Update/WSUS or your patch-management process as soon as practical, prioritizing internet-exposed and high-value systems; because the issue is in CISA's KEV catalog (added 2026-02-10), U.S. federal agencies must apply the vendor fix, applicable BOD 22-01 mitigations (including for cloud services), or discontinue use by the catalog due date. Until patched, follow Microsoft's mitigation guidance from vendor advisories and monitor for updates, since specific affected builds and the exploited security feature have not been detailed in the available data.