CVE-2025-66376

Published Jan 5, 2026

Last updated a month ago

Server

Overview

AI description

Automated description summarized from trusted sources.

CVE-2025-66376 is a stored Cross-Site Scripting (XSS) vulnerability found in Zimbra Collaboration (ZCS) affecting its Classic UI component. This flaw enables attackers to inject malicious scripts into the system through specially crafted HTML email messages. The vulnerability specifically exploits the way the Classic UI processes Cascading Style Sheets (CSS) `@import` directives embedded within these emails. When a user views a malicious email in the vulnerable Classic UI, the injected script can execute within the context of their browser session. This vulnerability is categorized under CWE-79, which refers to improper neutralization of input during web page generation, stemming from insufficient sanitization of CSS content in HTML email messages. Affected versions include Zimbra Collaboration (ZCS) 10 prior to version 10.0.18 and ZCS 10.1 prior to version 10.1.13.

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.
Source: cve@mitre.org
NVD status: Analyzed
Products: zimbra_collaboration_suite

Risk scores

CVSS 3.1

Type: Primary
Base score: 6.1
Impact score: 2.7
Exploitability score: 2.8
Vector string: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
Severity: MEDIUM

Known exploits

Data from CISA

Vulnerability name: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
Exploit added on: Mar 18, 2026
Exploit action due: Apr 1, 2026
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.

Weaknesses

cve@mitre.org: CWE-79

Hype score: Not currently trending

Configurations

[
  {
    "nodes": [
      {
        "cpeMatch": [
          {
            "criteria": "cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:*",
            "matchCriteriaId": "7D423DB3-FCD4-445F-A778-BC5F83E01953",
            "versionEndExcluding": "10.0.18",
            "versionStartIncluding": "10.0.0",
            "vulnerable": true
          },
          {
            "criteria": "cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:*",
            "matchCriteriaId": "7C3F6B1E-1671-461B-A093-7B6854C227FE",
            "versionEndExcluding": "10.1.13",
            "versionStartIncluding": "10.1.0",
            "vulnerable": true
          }
        ],
        "negate": false,
        "operator": "OR"
      }
    ]
  }
]

References

Sources include official advisories and independent security research.