CVE-2025-66376

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

Synacor — Zimbra Collaboration Suite (ZCS)

Added to KEV catalog: 18 March 2026
Federal remediation due date: 1 April 2026
Weakness classification (CWE): CWE-79

CISA Description

Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability in the Classic UI where attackers could abuse Cascading Style Sheets (CSS) @import directives in email HTML.

Required action

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

Notes

https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories ; https://nvd.nist.gov/vuln/detail/CVE-2025-66376

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