CVE-2021-26411

CVE-2021-26411 is a use-after-free (CWE-416) memory corruption vulnerability in Microsoft Internet Explorer's web rendering engine that can lead to remote code execution. It is triggered when a user, typically lured via a link, email, or watering-hole page, views attacker-controlled web content that corrupts memory, consistent with the CVSS profile requiring network access and user interaction. A successful attacker gains code execution in the context of the logged-on user, which in observed campaigns was chained into malware delivery (including exploit-kit payloads such as Dridex and VBA-based malware). Any Windows system that renders web content with Internet Explorer or its IE/MSHTML components (Edge is also listed among affected CPE products) is potentially affected, though specific version ranges are not provided in the source data. The flaw was exploited as a zero-day around Microsoft's March 2021 Patch Tuesday, was added to CISA KEV on 2021-11-03 with known ransomware use, and carries an 80.8% EPSS probability of exploitation within 30 days.

What to do: Apply Microsoft's March 2021 cumulative security updates for Internet Explorer, or any later cumulative update, across all Windows clients and servers, prioritizing user workstations per the CISA KEV required action. Review proxy and endpoint logs for visits to compromised watering-hole sites (notably Korean-language news sites) and for follow-on malware such as Dridex, and restrict or disable IE/legacy IE-mode rendering of untrusted web content where feasible.