A cross-site scripting (XSS) vulnerability in Web Client in Zimbra 9.0 allows a remote attacker to craft links in an E-Mail message or calendar invite to execute arbitrary JavaScript. The attack requires an A element containing an href attribute with a "www" substring (including the quotes) followed immediately by a DOM event listener such as onmouseover. This is fixed in 9.0.0 Patch 2.
https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories
https://wiki.zimbra.com/wiki/Zimbra_Releases/9.0.0/P2
https://blog.zimbra.com/2020/05/new-zimbra-9-kepler-patch-2/