CVE-2026-93647: Zimbra Collaboration Suite ZCS

Critical severity, CVSS 9.3. EPSS: 0.2% chance of exploitation in the next 30 days.

An unauthenticated calendar sender can place active markup in a COUNTER message's RFC From address. Selecting the message in Zimbra Classic triggers stored XSS, allowing the attacker to access mailbox data and act as the victim.

Affected products

• Zimbra Zimbra Collaboration Suite ZCS: before 10.1.21 (fixed in 10.1.21)

Published 2026-09-25. Last modified 2026-09-29.