What’s Vulnerable › Vulnerabilities
CVE-2026-93647: Zimbra Collaboration Suite Classic Web Client Stored Cross-Site Scripting via Crafted Calendar COUNTER Message From Address
- Severity: critical (CVSS 9.3 v3.1)
- Exploited in the wild: not listed in CISA KEV
- EPSS: 0.2% probability of exploitation in the next 30 days
- Public exploit or detection template: none known
- Published: 2026-09-25 · updated 2026-09-29
- Weakness: CWE-79
Description
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 Collaboration Suite (ZCS): before 10.1.21 — fixed in 10.1.21
How to fix
Upgrade to a fixed version: Zimbra Collaboration Suite (ZCS) 10.1.21. Check the vendor advisory for mitigations.
References
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