CVE-2025-66376 — Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
CVE-2025-66376: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
CISA Known Exploited Vulnerability (KEV)
| Vendor / project | Synacor |
| Product | Zimbra Collaboration Suite (ZCS) |
| Date added | 2026-03-18 |
| Due date | 2026-04-01 |
| Ransomware campaign use | Unknown |
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 (CISA)
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
References
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-66376
- KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog