March 18, 2026 · Applied Cybernetics Group
CVE-2025-66376 — Synacor Zimbra Collaboration Suite (ZCS)
Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
- Added to KEV
2026-03-18- Federal due date
2026-04-01- Vendor
- Synacor
- Product
- Zimbra Collaboration Suite (ZCS)
- EPSS
- 93.5th percentile (score 0.109, as of
2026-06-08) - NVD CVSS v3.1
- —
- Ransomware use
- Unknown
- Upstream
- https://nvd.nist.gov/vuln/detail/CVE-2025-66376
CISA short 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.