CVE-2025-66376

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

High 7.2
Exploited: added to CISA KEV 18 Mar 2026

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.

Key facts

Published: 5 Jan 2026
Last changed: 19 Mar 2026
Assigned by: mitre
KEV added: 18 Mar 2026
KEV fix due: 1 Apr 2026
EPSS: 20.227% likely to be exploited in the next 30 days, higher than 97.509% of CVEs (scores for 15 Nov 2026)
SSVC (CISA): Exploitation: active; Automatable: no; Technical impact: partial

Severity scores

Each score is shown as its source gave it. They are not averaged or merged.

7.2CVSS 3.1, Highfrom the CNA (mitre)CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N

What to do

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 KEV required action

Historical context and remediation

This reference retains the original CVE publication date. A recent record update does not mean a new attack occurred.

No separately sourced impact summary is available on this page yet. Consult the description, version data and dated exploitation evidence.

Version statuses below come from the CNA. An “unaffected” version is not necessarily a currently supported release or proof of a patch date. EPSS is a dated risk estimate, not a count of historical attacks.

Read the original CVE record.

Affected products

Vendor	Product	Versions
Zimbra	Collaboration	Default status: unaffected 10.0 up to but excluding 10.0.18 (affected) 10.1 up to but excluding 10.1.13 (affected)

Timeline

5 Jan 2026 Published
18 Mar 2026 CVE-2025-66376 added to CISA KEV
18 Mar 2026 Added to the CISA KEV catalogue

Weakness

CWE-79

Practice this bug class

HackZoneLabs has a hands-on lab on XSS (stored, reflected, DOM) (CWE-79).

Open the learning platform