Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability

Technical Severity

CVSS v3.1 Metrics

HIGH

7.2 / 10

Minimal Risk Critical

Vector Specification

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

Exploitation Likelihood

EPSS Prediction

10.01 %

Predictive Probability

Percentile Rank

93.0 th

Documented as more likely to be exploited than 93.0% of known CVEs.

Detection Date

Mar 18, 2026

Remediation Due

Apr 01, 2026

CISA Catalog Active

Threat Analysis

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.

Remediation Directive

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

External Intelligence

https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories

NVD

National Vulnerability Database

https://nvd.nist.gov/vuln/detail/CVE-2025-66376