CVE-2025-66376

HIGH7.2

CISA KEV

Published 2026-01-05 · Updated 2026-10-07 · Source cve@mitre.org

Summary

CVE-2025-66376 is a high-severity (CVSS 7.2) vulnerability in Synacor Zimbra Collaboration Suite (ZCS). CISA added it to the Known Exploited Vulnerabilities catalog on March 18, 2026, which means exploitation in the wild has been confirmed; US federal agencies had to remediate it by April 1, 2026. CISA does not currently list it as used in ransomware campaigns. Synacor has 19 vulnerabilities in the KEV catalog, 6 of them linked to ransomware.

All 19 known-exploited Synacor vulnerabilities →

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.

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

CWE-79

CISA Known-Exploited Vulnerability

Product: Synacor — Zimbra Collaboration Suite (ZCS)

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

Date added: 2026-03-18 · Due: 2026-04-01

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.

References

View on NVD

More exploited Synacor vulnerabilities

Most recently added to CISA KEV

CVE-2026-73570
Zimbra Collaboration Suite (ZCS) — Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability
added 2026-08-21
CVE-2025-48700
Zimbra Collaboration Suite (ZCS) — Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
added 2026-04-20
CVE-2020-7796
Zimbra Collaboration Suite — Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery Vulnerability
added 2026-02-17
CVE-2025-68645
Zimbra Collaboration Suite (ZCS) — Synacor Zimbra Collaboration Suite (ZCS) PHP Remote File Inclusion Vulnerability
added 2026-01-22
CVE-2025-27915
Zimbra Collaboration Suite (ZCS) — Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
added 2025-10-07
CVE-2019-9621
Zimbra Collaboration Suite (ZCS) — Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery (SSRF) Vulnerability
added 2025-07-07

View all →

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