CVE-2025-66376

Name: CVE-2025-66376
Creator: NVD / NIST
Published: 2026-01-05T15:15:44.903+00:00
License: https://creativecommons.org/publicdomain/zero/1.0/

MEDIUMCVSS 6.1/10Actively ExploitedEPSS 12.01%

Last modified Jun 17, 2026

CVE-2025-66376 is a medium-severity vulnerability rated 6.1/10 on the CVSS scale. 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.. CISA has confirmed active exploitation in the wild. EPSS estimates a 12.01% chance of exploitation in the next 30 days.

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.

Metrics

CVSS 3.1

6.1/10

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

EPSS Probability

12.01%

95.6th percentile

Probability of exploitation in the next 30 days. Learn more

Exploitation Status

This vulnerability is listed in CISA’s Known Exploited Vulnerabilities catalog, confirming active exploitation in the wild. Federal agencies must remediate by Apr 1, 2026.

Weakness Enumeration

CWE-79

Affected Software

Vendor	Product	Versions
Synacor	Zimbra Collaboration Suite	>= 10.0.0, < 10.0.18
Synacor	Zimbra Collaboration Suite	>= 10.1.0, < 10.1.13

References

https://wiki.zimbra.com/wiki/Security_CenterRelease Notes, Vendor Advisory
https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_FixesRelease Notes
https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_FixesRelease Notes
https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_PolicyProduct
https://wiki.zimbra.com/wiki/Zimbra_Security_AdvisoriesVendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376US Government Resource

Timeline

Published: Jan 5, 2026
Last Modified: Jun 17, 2026
Status: Analyzed

Frequently Asked Questions

What is CVE-2025-66376?

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.

How severe is CVE-2025-66376?

CVE-2025-66376 has a CVSS score of 6.1/10 (MEDIUM severity). The EPSS model estimates a 12.01% probability of exploitation in the next 30 days. This vulnerability is listed in CISA's Known Exploited Vulnerabilities catalog.

How do I fix CVE-2025-66376?

Check the vendor references and advisories linked above for patched versions and mitigation guidance. You can also run a Strix scan to test if your systems are affected.

Are you affected by CVE-2025-66376?

Run a free Strix scan to check your systems for this vulnerability.

Scan your code now

Source: NVD / NIST