CVE-2023-24880

CVE-2023-24880 is a security feature bypass (incorrect authorization, CWE-863) in Windows SmartScreen: when a user opens a file carrying Mark-of-the-Web — such as an email attachment or a downloaded file — Windows fails to display the SmartScreen 'Open File – Security Warning' prompt that normally precedes execution. An attacker who can get a user to open a crafted malicious file therefore gains the ability to run attacker-chosen code on that machine without the SmartScreen warning, defeating a core client-side defense; the bypass was typically chained with a lure or another flaw to deliver malware, including loaders feeding ransomware operations. Any user or organization running the affected Windows 10, Windows 11, or Windows Server builds is affected, though exploitation requires local access and user interaction (CVSS 4.4, local attack vector). The flaw was a zero-day exploited in the wild before Microsoft patched it in the March 2023 Patch Tuesday release — one of two actively exploited flaws fixed that month — and Google researchers reported a ransomware gang exploited it; CISA added it to the Known Exploited Vulnerabilities Catalog on 2023-03-14 with known ransomware use, and EPSS rates the probability of exploitation within 30 days at 78.2% (100th percentile). No public proof-of-concept is known, but confirmed in-the-wild exploitation means defenders should treat it as actively targeted.

What to do: Apply the March 2023 Windows security updates to all affected Windows 10 (1607, 1809, 20H2, 21H2, 22H2), Windows 11 (21H2, 22H2), and Windows Server 2016/2019/2022 systems via Windows Update, WSUS, or your patch-management tooling, and verify coverage in your inventory — this is CISA's required action for KEV. Until patched, treat any host whose users open untrusted email attachments or downloads as exposed, since the bypass silently skips the SmartScreen warning; updating is the only complete fix, with no published configuration workaround.