Roundcube Webmail before 1.6.20 and 1.7.x before 1.7.5 is affected by an improper authentication vulnerability in multi-host installations. When a user logs in with an alias address, rcube_user::query() matched the address against identity records without qualifying the lookup by IMAP host, so a login could be resolved to a user account belonging to a different IMAP host. Upstream fixed this in the commit “Fix bug where an alias login wasn’t qualified by IMAP host”.
https://roundcube.net/news/2026/10/19/security-updates-1.6.20-and-1.7.5
https://github.com/roundcube/roundcubemail/releases/tag/1.7.5
https://github.com/roundcube/roundcubemail/releases/tag/1.6.20
https://github.com/roundcube/roundcubemail/commit/cb235cbfef88cbf78236dc67d3b667bf3dc61ddd
https://github.com/roundcube/roundcubemail/commit/453c413d6851cf603bebdb15e58381f5ef9b8094