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

Synacor Zimbra Collaboration Suite (ZCS)

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. Added to CISA KEV on 2026-03-18 (federal deadline 2026-04-01).

First seen: 18 Mar 2026
Last update: 18 Mar 2026, 12:00 UTC
Identifiers: CVE-2025-66376
Source: CISA KEV
On the menu as: Enterprise apps

Check this repository for exposure to one security incident from pwned.coffee. Report first, change nothing until I say so.

## Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
Severity: high, exploited in the wild. Patch status: patched.
Affected: Synacor Zimbra Collaboration Suite (ZCS)
Ids: CVE-2025-66376

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. Added to CISA KEV on 2026-03-18 (federal deadline 2026-04-01).

## Steps
1. This touches infrastructure (erp). Look in terraform, ansible, cloud-init, Dockerfiles and docs for the product and version we run. If it isn't in the repo, say so and list what a human should check on the box.

## Report
A table: file, product or package, version in use, affected yes/no, exact fix. Then anything a human has to check outside the repo.

If you have the pwned.coffee MCP server (https://pwned.coffee/mcp), call lookup_cve("CVE-2025-66376") for the latest, and check_repo with this repo's lockfiles, Dockerfiles and workflows for a full receipt.
Sources: https://nvd.nist.gov/vuln/detail/CVE-2025-66376 https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories
https://pwned.coffee/i/synacor-zimbra-collaboration-suite-zcs-cross-site-script-cve-2025-66376

Sources

Totalone hot coffee