CVE-2025-66376: CWE-79 Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') in Zimbra Collaboration
A persistent cyberespionage campaign tracked as CL-STA-1114, overlapping with Russian threat actor activity known as Void Blizzard and LAUNDRY BEAR, has been targeting Zimbra webmail in government, defense, transportation, and financial organizations. The campaign focuses on NATO member states, Ukraine, Commonwealth of Independent States countries, and Africa. Attackers exploit CVE-2025-66376, a vulnerability in Zimbra Collaboration Suite, using zero-click phishing emails that automatically inject malicious JavaScript payloads without user interaction. The payload exfiltrates sensitive data including login credentials, email archives, CSRF tokens, 2FA scratch codes, and 90 days of email history to command and control servers. Active since 2024, the campaign targeting Zimbra servers began in July 2025, utilizing HTML attachments with obfuscated Base64-encoded scripts that deploy SVG elements to inject the JavaScript into victims' browsers.
AI Analysis
Technical Summary
This vulnerability (CVE-2025-66376) affects Zimbra Collaboration Suite versions 10.0 prior to 10.0.18 and 10.1 prior to 10.1.13. It is a stored Cross-site Scripting (XSS) flaw caused by improper input neutralization during web page generation, specifically through CSS @import directives embedded in HTML email messages displayed in the Classic UI. An attacker can exploit this without authentication or user interaction to execute arbitrary scripts in the victim's browser, risking confidentiality and session integrity. The CVSS 3.1 base score is 7.2, reflecting high severity with network attack vector, low attack complexity, no privileges required, no user interaction, and impact on confidentiality and integrity.
Potential Impact
Successful exploitation allows an attacker to execute arbitrary scripts in the context of the victim's browser when viewing crafted HTML email messages. This can lead to theft of sensitive data or session hijacking. The vulnerability does not affect availability. No known active exploits have been reported.
Mitigation Recommendations
No official patch or remediation details are provided in the available data. Patch status is not yet confirmed — check the Zimbra vendor advisory for current remediation guidance. Until a fix is applied, consider restricting access to vulnerable versions and exercising caution when handling HTML emails in the Classic UI.
Indicators of Compromise
- domain: zimbra-metadata.com
- domain: emailanalytics.com.ua
- domain: mailnalysis.com
- domain: analyticemailmeter.com
- domain: zimbrastat.com
- domain: zimbrasoft.com.ua
- cve: CVE-2025-66376
- domain: istc-cloud.com
- domain: synacorzimbra.nl
- domain: zmailanalytics.com
CVE-2025-66376: CWE-79 Improper Neutralization of Input During Web Page Generation (XSS or 'Cross-site Scripting') in Zimbra Collaboration
Description
A persistent cyberespionage campaign tracked as CL-STA-1114, overlapping with Russian threat actor activity known as Void Blizzard and LAUNDRY BEAR, has been targeting Zimbra webmail in government, defense, transportation, and financial organizations. The campaign focuses on NATO member states, Ukraine, Commonwealth of Independent States countries, and Africa. Attackers exploit CVE-2025-66376, a vulnerability in Zimbra Collaboration Suite, using zero-click phishing emails that automatically inject malicious JavaScript payloads without user interaction. The payload exfiltrates sensitive data including login credentials, email archives, CSRF tokens, 2FA scratch codes, and 90 days of email history to command and control servers. Active since 2024, the campaign targeting Zimbra servers began in July 2025, utilizing HTML attachments with obfuscated Base64-encoded scripts that deploy SVG elements to inject the JavaScript into victims' browsers.
CVSS v3.1
Score 7.2high
Affected software
pkg:rpm/zimbra/collaborationRun on your own infrastructure? Check whether these packages are installed with threat-finder — our free open-source scanner.
Weaknesses
AI-Powered Analysis
Machine-generated threat intelligence
Technical Analysis
This vulnerability (CVE-2025-66376) affects Zimbra Collaboration Suite versions 10.0 prior to 10.0.18 and 10.1 prior to 10.1.13. It is a stored Cross-site Scripting (XSS) flaw caused by improper input neutralization during web page generation, specifically through CSS @import directives embedded in HTML email messages displayed in the Classic UI. An attacker can exploit this without authentication or user interaction to execute arbitrary scripts in the victim's browser, risking confidentiality and session integrity. The CVSS 3.1 base score is 7.2, reflecting high severity with network attack vector, low attack complexity, no privileges required, no user interaction, and impact on confidentiality and integrity.
Potential Impact
Successful exploitation allows an attacker to execute arbitrary scripts in the context of the victim's browser when viewing crafted HTML email messages. This can lead to theft of sensitive data or session hijacking. The vulnerability does not affect availability. No known active exploits have been reported.
Mitigation Recommendations
No official patch or remediation details are provided in the available data. Patch status is not yet confirmed — check the Zimbra vendor advisory for current remediation guidance. Until a fix is applied, consider restricting access to vulnerable versions and exercising caution when handling HTML emails in the Classic UI.
Technical Details
- Data Version
- 5.2
- Assigner Short Name
- mitre
- Date Reserved
- 2025-11-28T00:00:00.000Z
- Cvss Version
- 3.1
- State
- PUBLISHED
Indicators of Compromise
Domain
| Value | Description | Copy |
|---|---|---|
domainzimbra-metadata.com | — | |
domainemailanalytics.com.ua | — | |
domainmailnalysis.com | — | |
domainanalyticemailmeter.com | — | |
domainzimbrastat.com | — | |
domainzimbrasoft.com.ua | — | |
domainistc-cloud.com | — | |
domainsynacorzimbra.nl | — | |
domainzmailanalytics.com | — |
Cve
| Value | Description | Copy |
|---|---|---|
cveCVE-2025-66376 | — |
Threat ID: 695bd2af3dc84013b27cfcec
Added to database: 01/05/2026, 15:03:11 UTC
Last enriched: 07/24/2026, 20:52:34 UTC
Last updated: 08/22/2026, 22:52:10 UTC
Views: 268
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