CVE-2024-27443: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting (XSS) Vulnerability

Medium severity, CVSS 6.1. Actively exploited: in CISA KEV since 2025-05-19. EPSS: 23.6% chance of exploitation in the next 30 days.

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.

Affected products

• Zimbra Collaboration: from 10.0.0, before 10.0.7 (fixed in 10.0.7); version 9.0.0 only

Published 2024-08-12. Last modified 2026-06-17.