CVE detail
CVE-2025-66376: Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
Source: CISA Known Exploited Vulnerabilities catalog · back to feed
Vendor / product
Synacor · Zimbra Collaboration Suite (ZCS)
- Date added (KEV)
- Mar 18, 2026
- CISA due date
- Apr 01, 2026
- Ransomware campaign use
- Unknown
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.
Scorifya interpretation
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Plain English
Technical detail
From CISA
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.
https://wiki.zimbra.com/wiki/Zimbra_Security_Advisories ; https://nvd.nist.gov/vuln/detail/CVE-2025-66376
See what attackers can see on your domain
This vulnerability is on CISA's Known Exploited Vulnerabilities list, so it is being exploited in the wild right now. Scorifya can't test for Synacor directly, but in about 30 seconds it shows what your own domain exposes publicly across TLS, security headers, DNS, and cookies: the surface attackers probe first.
SOC 2 compliance
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See Scorifya Controls →References
- https://wiki.zimbra.com/wiki/Security_CenterRelease NotesVendor Advisory
- https://wiki.zimbra.com/wiki/Zimbra_Security_AdvisoriesVendor 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
Other recent CVEs from Synacor
- CVE-2025-48700Zimbra Collaboration Suite (ZCS), Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
- CVE-2020-7796Zimbra Collaboration Suite, Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery Vulnerability
- CVE-2025-68645Zimbra Collaboration Suite (ZCS), Synacor Zimbra Collaboration Suite (ZCS) PHP Remote File Inclusion Vulnerability
- CVE-2025-27915Zimbra Collaboration Suite (ZCS), Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
- CVE-2019-9621Zimbra Collaboration Suite (ZCS), Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery (SSRF) Vulnerability