ACTIVELY EXPLOITED
CVE-2025-66376: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
| Vendor | Synacor |
|---|---|
| Product | Zimbra Collaboration Suite (ZCS) |
| Actively exploited | Yes |
| Added to CISA KEV | 18 Mar 2026 |
| CISA federal deadline | 1 Apr 2026 |
| Weakness (CWE) | CWE-79 |
Required action (CISA's text)
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Description (NVD)
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.
SOURCES
Other Synacor flaws
- CVE-2026-73570: Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability
- CVE-2025-48700: Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
- CVE-2020-7796: Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery Vulnerability
- CVE-2025-68645: Synacor Zimbra Collaboration Suite (ZCS) PHP Remote File Inclusion Vulnerability
- CVE-2025-27915: Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
Data from NVD, CISA KEV, FIRST EPSS and vendor advisories. Updated 10 Nov 2026.