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Known Exploited Vulnerability
7.2
HIGH CVSS 3.1
CVE-2025-66376
Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability - [Actively Exploited]
Overview
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.

Details
INFO

Published Date :

Jan. 5, 2026, 3:15 p.m.

Last Modified :

March 18, 2026, 8:13 p.m.

Remotely Exploit :

Yes !

Source :

[email protected]
CISA Notification
CISA KEV (Known Exploited Vulnerabilities)

For the benefit of the cybersecurity community and network defenders—and to help every organization better manage vulnerabilities and keep pace with threat activity—CISA maintains the authoritative source of vulnerabilities that have been exploited in the wild.

Description :

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.

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.

Known Ransomware Campaign Use:

Unknown

Notes :

https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories ; https://nvd.nist.gov/vuln/detail/CVE-2025-66376

Impact
Affected Products

The following products are affected by CVE-2025-66376 vulnerability. Even if cvefeed.io is aware of the exact versions of the products that are affected, the information is not represented in the table below.

ID Vendor Product Action
1 Zimbra collaboration
1 Synacor zimbra_collaboration_suite
: Total Affected Vendor : 2 | Products : 2
Scoring
CVSS Scores
The Common Vulnerability Scoring System is a standardized framework for assessing the severity of vulnerabilities in software and systems. We collect and displays CVSS scores from various sources for each CVE.
Score Version Severity Vector Exploitability Score Impact Score Source
CVSS 3.1 HIGH [email protected]
CVSS 3.1 MEDIUM [email protected]
Solution
Update Zimbra Collaboration to a patched version to fix stored XSS via CSS @import.
  • Update Zimbra Collaboration to version 10.0.18 or higher.
  • Update Zimbra Collaboration to version 10.1.13 or higher.
Public PoC/Exploit Available at Github

CVE-2025-66376 has a 1 public PoC/Exploit available at Github. Go to the Public Exploits tab to see the list.

References
References to Advisories, Solutions, and Tools

Here, you will find a curated list of external links that provide in-depth information, practical solutions, and valuable tools related to CVE-2025-66376.

URL Resource
https://wiki.zimbra.com/wiki/Security_Center Release Notes Vendor Advisory
https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_Fixes Release Notes
https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_Fixes Release Notes
https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_Policy Product
https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories Vendor Advisory
https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376 US Government Resource
CWE - Common Weakness Enumeration

While CVE identifies specific instances of vulnerabilities, CWE categorizes the common flaws or weaknesses that can lead to vulnerabilities. CVE-2025-66376 is associated with the following CWEs:

Common Attack Pattern Enumeration and Classification (CAPEC)

Common Attack Pattern Enumeration and Classification (CAPEC) stores attack patterns, which are descriptions of the common attributes and approaches employed by adversaries to exploit the CVE-2025-66376 weaknesses.

We scan GitHub repositories to detect new proof-of-concept exploits. Following list is a collection of public exploits and proof-of-concepts, which have been published on GitHub (sorted by the most recently updated).

Profile Photo
DevGreick/devgreick

None

Python

Updated: 6 days, 8 hours ago
1 stars 0 fork 0 watcher
Born at : Oct. 29, 2024, 8:10 p.m. This repo has been linked 11 different CVEs too.

Results are limited to the first 15 repositories due to potential performance issues.

The following list is the news that have been mention CVE-2025-66376 vulnerability anywhere in the article.

  • Daily CyberSecurity
The Invisible Breach: ‘Operation GhostMail’ Uses Zero-Click XSS to Hijack Ukrainian Webmail

Image: Seqrite Labs A sophisticated cyberespionage campaign, dubbed Operation GhostMail, has been detected targeting critical government infrastructure in Ukraine. Security researchers at Seqrite Labs ... Read more

Published Date: Mar 20, 2026 (1 week ago)
  • CybersecurityNews
Russian APT Exploits Zimbra XSS to Target Ukrainian Government in ‘Operation GhostMail’

A Russian state-linked threat actor has launched a targeted cyberattack against a Ukrainian government agency, exploiting a cross-site scripting (XSS) vulnerability in Zimbra Collaboration Suite to st ... Read more

Published Date: Mar 20, 2026 (1 week, 1 day ago)
  • CybersecurityNews
CISA Warns of Zimbra Collaboration Suite Vulnerability Exploited in Attacks

CISA Warns Zimbra Collaboration Suite Vulnerability Exploit CISA has added a high-severity vulnerability affecting the Zimbra Collaboration Suite (ZCS) to its Known Exploited Vulnerabilities (KEV) cat ... Read more

Published Date: Mar 19, 2026 (1 week, 1 day ago)
  • security.nl
Gebruikers van Zimbra-webmail aangevallen via XSS-kwetsbaarheid

Gebruikers van Zimbra-webmail zijn het doelwit van aanvallen waarbij er misbruik wordt gemaakt van een cross-site scripting (XSS) kwetsbaarheid. Dat meldt het Amerikaanse cyberagentschap CISA. Eind vo ... Read more

Published Date: Mar 19, 2026 (1 week, 1 day ago)
  • The Hacker News
CISA Warns of Zimbra, SharePoint Flaw Exploits; Cisco Zero-Day Hit in Ransomware Attacks

The U.S. Cybersecurity and Infrastructure Security Agency (CISA) has urged government agencies to apply patches for two security flaws impacting Synacor Zimbra Collaboration Suite (ZCS) and Microsoft ... Read more

Published Date: Mar 19, 2026 (1 week, 2 days ago)
  • TheCyberThrone
CISA adds Three Vulnerabilities to KEV Catalog

OverviewCISA has expanded its Known Exploited Vulnerabilities (KEV) catalog with three new entries this week, spanning enterprise collaboration, file transfer infrastructure, and email collaboration p ... Read more

Published Date: Mar 19, 2026 (1 week, 2 days ago)
  • Daily CyberSecurity
Exploited in the Wild: CISA Warns of Active Attacks on Microsoft SharePoint and Zimbra

The Cybersecurity and Infrastructure Security Agency (CISA) has officially expanded its Known Exploited Vulnerabilities (KEV) Catalog, adding two high-risk flaws that are currently being weaponized by ... Read more

Published Date: Mar 19, 2026 (1 week, 2 days ago)

Results are limited to the first 20 news articles due to potential performance issues.

The following table lists the changes that have been made to the CVE-2025-66376 vulnerability over time.

Vulnerability history details can be useful for understanding the evolution of a vulnerability, and for identifying the most recent changes that may impact the vulnerability's severity, exploitability, or other characteristics.

  • Initial Analysis by [email protected]

    Mar. 18, 2026

    Action Type Old Value New Value
    Added CVSS V3.1 AV:N/AC:L/PR:N/UI:R/S:C/C:L/I:L/A:N
    Added CPE Configuration OR *cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:* versions from (including) 10.0.0 up to (excluding) 10.0.18 *cpe:2.3:a:synacor:zimbra_collaboration_suite:*:*:*:*:*:*:*:* versions from (including) 10.1.0 up to (excluding) 10.1.13
    Added Reference Type MITRE: https://wiki.zimbra.com/wiki/Security_Center Types: Release Notes, Vendor Advisory
    Added Reference Type MITRE: https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_Fixes Types: Release Notes
    Added Reference Type MITRE: https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_Fixes Types: Release Notes
    Added Reference Type MITRE: https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_Policy Types: Product
    Added Reference Type MITRE: https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories Types: Vendor Advisory
    Added Reference Type CISA-ADP: https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376 Types: US Government Resource
  • CVE Modified by 134c704f-9b21-4f2e-91b3-4a467353bcc0

    Mar. 18, 2026

    Action Type Old Value New Value
    Added Reference https://www.cisa.gov/known-exploited-vulnerabilities-catalog?field_cve=CVE-2025-66376
  • New CVE Received by [email protected]

    Jan. 05, 2026

    Action Type Old Value New Value
    Added 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.
    Added CVSS V3.1 AV:N/AC:L/PR:N/UI:N/S:C/C:L/I:L/A:N
    Added CWE CWE-79
    Added Reference https://wiki.zimbra.com/wiki/Security_Center
    Added Reference https://wiki.zimbra.com/wiki/Zimbra_Releases/10.0.18#Security_Fixes
    Added Reference https://wiki.zimbra.com/wiki/Zimbra_Releases/10.1.13#Security_Fixes
    Added Reference https://wiki.zimbra.com/wiki/Zimbra_Responsible_Disclosure_Policy
    Added Reference https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories
EPSS is a daily estimate of the probability of exploitation activity being observed over the next 30 days. Following chart shows the EPSS score history of the vulnerability.
CVSS
Vulnerability Scoring Details
Base CVSS Score: 7.2
Attack Vector
Attack Complexity
Privileges Required
User Interaction
Scope
Confidentiality Impact
Integrity Impact
Availability Impact