AdvisoriesCVE-2025-66376

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

SynacorZimbra Collaboration Suite (ZCS)Added March 18, 2026

CISA Known Exploited Vulnerabilities Data

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.

CISA Due Date

April 1, 2026 (federal agency requirement)

Known Ransomware Campaign Use

Unknown

Notes

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

External References

View on CISA KEV View CVE-2025-66376 on NVD Search MITRE ATT&CK

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Data sourced from the CISA Known Exploited Vulnerabilities catalog. CISA does not endorse any commercial product or service.