An XSS vulnerability exists in the Webmail component of Zimbra Collaboration Suite before 8.8.15 Patch 11. It allows an attacker to inject executable JavaScript into the account name of a user's profile. The injected code can be reflected and executed when changing an e-mail signature.
https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories
https://wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P4