Cross-Site Scripting Vulnerability in Zimbra Collaboration Suite
CVE-2026-93647

9.3CRITICAL

Key Information:

Vendor

Zimbra

Status
Zimbra Collaboration Suite (zcs)
Vendor
CVE Published:
25 September 2026

What is CVE-2026-93647?

An unauthenticated attacker can exploit a vulnerability in the Zimbra Collaboration Suite by injecting active markup into the RFC From address of a COUNTER message. When the message is accessed in Zimbra Classic, it triggers stored XSS, potentially granting the attacker unauthorized access to the victim's mailbox data and the ability to impersonate the victim.

Affected Version(s)

Zimbra Collaboration Suite (ZCS) 0 < 10.1.21

References

https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories
vendor-advisory

CVSS V3.1

Score:
9.3
Severity:
CRITICAL
Confidentiality:
High
Integrity:
High
Availability:
High
Attack Vector:
Network
Attack Complexity:
Low
Privileges Required:
None
User Interaction:
Required
Scope:
Changed

Timeline

  • Vulnerability published

  • Vulnerability Reserved

Credit

Jonah Burgess (CryptoCat), Senior Security Researcher, Rapid7
.