CVE-2025-66376
Actively exploited. CVE-2025-66376 is listed in the CISA Known Exploited Vulnerabilities catalog (added 2026-03-18) — exploitation has been observed in the wild, and US federal agencies are required to remediate it under BOD 22-01. Treat patching as urgent.
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.
CSIRTS triage
- What
- 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.
- Who is affected
- Users of Zimbra Collaboration Suite are at risk.
- Urgency
- Immediate remediation is necessary due to confirmed exploitation and critical severity.
- Action
- Update Zimbra Collaboration Suite to the latest version.
AI-assisted analysis generated from the source advisory — verify against the original.
⚡ Watch CVE-2025-66376
Get an email if CVE-2025-66376 is added to CISA KEV, gains public exploit code, or a new advisory cites it — max one per day, one-click unsubscribe.
Exploitation outlook
- Exploitation confirmedAlready exploited in the wild (CISA KEV) — the prediction phase is over. Patch now. Riskier than 96% of all EPSS-scored CVEs.
Advisory coverage (1)
- criticalexploitedCVE-2025-66376: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerabilitycisa-kev · 2026-03-18
External references
Embed the live status
— this badge updates automatically when the KEV or exploit status changes. How to embed it →
[](https://www.csirts.com/cve/CVE-2025-66376)