In HordeCrypt before 2.7.6, as used in Horde Groupware Webmail Edition 5.x through 5.2.17, OS Command Injection can occur if the user has PGP features enabled in the user's preferences, and has enabled the "Should PGP signed messages be automatically verified when viewed?" preference. To exploit this vulnerability, an attacker can send a PGP signed email (that is maliciously crafted) to the Horde user, who then must either view or preview it.

Multiple cross-site scripting (XSS) vulnerabilities in Horde Internet Mail Program (IMP) before 6.1.8, as used in Horde Groupware Webmail Edition before 5.1.5, allow remote attackers to inject arbitrary web script or HTML via an unspecified flag in the basic (1) mailbox or (2) message view.

Multiple cross-site scripting (XSS) vulnerabilities in Horde Internet Mail Program (IMP) before 6.1.8, as used in Horde Groupware Webmail Edition before 5.1.5, allow remote attackers to inject arbitrary web script or HTML via (1) unspecified flags or (2) a mailbox name in the dynamic mailbox view.

Horde Groupware Web mail 5.1.2 has CSRF with requests to change permissions

Multiple CSRF issues in Horde Groupware Webmail Edition 5.1.2 and earlier in basic.php.