CVE-2025-66376—Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability

Vulnerability Name

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

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.

Known To Be Used in Ransomware Campaigns?

Ransomware Status:

Unknown

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.

Additional Notes

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

Related News Articles

• Russian Hackers Exploit Microsoft OWA Flaw to Keep Mailbox Access After Credential RotationJuly 30, 2026
• Russian hackers exploit Exchange OWA zero-day for long-term mailbox accessJuly 29, 2026
• Russian hackers exploit Zimbra zero-click flaw for email theftJuly 23, 2026
• Russian hackers exploit unpatched Zimbra servers to steal emailsJuly 24, 2026
• Zimbra urges customers to patch critical web client XSS flawJuly 10, 2026

Related Weaknesses

• CWE-79