CVE-2025-66376 — Synacor Zimbra Collaboration Suite (ZCS): Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
CVE-2025-66376 — 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.
What This Means For You
- CISA has confirmed active exploitation — immediate patching required.
- Added to CISA KEV catalog — federal agencies must remediate by 2026-04-01.
Indicators of Compromise
| ID | Type | Indicator |
|---|---|---|
| CVE-2025-66376 | XSS | Synacor Zimbra Collaboration Suite (ZCS) Classic UI, abuse of CSS @import directives in email HTML |
Source & Attribution
| Source Platform | CISA |
| Channel | CISA KEV |
| Channel ID | cisa-kev |
| Message ID | 202566376 |
| Published | March 18, 2026 at 14:00 UTC |
| Original Link | https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories |
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