CVE-2024-42009

CVE-2024-42009 is a cross-site scripting (CWE-79) vulnerability in Roundcube Webmail versions through 1.5.7 and 1.6.x through 1.6.7, caused by a desanitization issue in message_body() in program/actions/mail/show.php. An attacker sends a specially crafted email, and when the victim opens it in the Roundcube interface, injected script runs in the context of the victim's webmail session (no privileges are required, but user interaction is needed, per the CVSS UI:R vector). Successful exploitation lets the attacker steal the victim's emails and send messages as the victim, and related reporting notes that, chained with the companion flaw CVE-2024-42008, attackers can compromise email accounts and passwords. Any organization or provider self-hosting an affected Roundcube version is exposed, including universities, hosting providers, enterprises, and government mail systems. Exploitation is confirmed in the wild: CISA added the flaw to its Known Exploited Vulnerabilities catalog on 2025-06-09, EPSS is 82.9% (100th percentile), and recent headlines describe suspected China-aligned espionage activity using Roundcube exploit chains against universities.

What to do: Upgrade Roundcube to a point release newer than 1.6.7 on the 1.6.x line or newer than 1.5.7 on the 1.5.x line (the latest vendor release of each branch), per vendor instructions; organizations under BOD 22-01 must apply the required mitigations by the KEV due date or discontinue use. Also patch the companion issue CVE-2024-42008 to prevent chained account compromise. Review webmail access logs for suspicious requests to the mail show handler, check sent-mail folders for messages sent unexpectedly as users, and rotate sessions/credentials for potentially targeted accounts.