Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability

A remote attacker, without authentication, can achieve partial data exposure, partial data tampering. Federal agencies are required to remediate by 2025-06-09 under CISA BOD 22-01.

This is a Cross-Site Scripting (XSS) (CWE-79) vulnerability in Synacor Zimbra Collaboration Suite (ZCS). An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0. A Cross-Site Scripting (XSS) vulnerability exists in the CalendarInvite feature of the Zimbra webmail classic user interface, because of improper input validation in the handling of the calendar header. An attacker can exploit this via an email message containing a crafted calendar header with an embedded XSS payload. When a victim views this message in the Zimbra webmail classic interface, the payload is executed in the context of the victim's session, potentially leading to execution of arbitrary JavaScript code. Exploitation requires remote network access, low attack complexity, no authentication required, and user interaction required.

Probably yes if any of these apply:

Active exploitation documented in the wild. Threat-research write-up: https://www.welivesecurity.com/en/eset-research/operation-roundpress/