CVE-2025-66376
HighActively exploited (CISA KEV)
Description
Zimbra Collaboration (ZCS) 10 before 10.0.18 and 10.1 before 10.1.13 allows Classic UI stored XSS via Cascading Style Sheets (CSS) @import directives in an HTML e-mail message.
SeverityHigh
CVSS7.2
Exploit probability—
Product
Synacor Zimbra Collaboration Suite (ZCS)
PublishedJan 5, 2026
First seenJan 5, 2026
Added to KEVMar 18, 2026
Weakness typeCWE-79Cross-site scripting (XSS)
How to fix
CISA 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.
CISA due date: Apr 1, 2026Update
- synacor zimbra_collaboration_suite10.0.18, 10.1.13 or later
Affected products
| Product | Affected versions | Fixed in |
|---|---|---|
| synacor zimbra_collaboration_suite | 10.0.0 ≤ v < 10.0.18, 10.1.0 ≤ v < 10.1.13 | 10.0.18, 10.1.13 |
Check your version
Choose the product and enter the version you run to see whether it falls in the affected range.
In the Intelligence 360 plan
Attack Surface Management
See the assets tied to your domains, the technologies they run and known vulnerabilities in one list.