CVE-2025-66376 · netVigilance record NV26-0060

Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting

past due

What to do

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

CISA deadline 2026-04-01 · passed 5 months ago · applies to US federal civilian agencies; used elsewhere as a reference SLA

What happened

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.

Who is affected

Synacor Zimbra Collaboration Suite (ZCS). Affected version ranges are listed in the vendor advisory and the NVD entry linked under Sources.

Weakness class: CWE-79.

Timeline

2026-03-18
Added to CISA KEVExploitation in the wild confirmed by CISA
2026-04-01
CISA remediation deadlinepassed 5 months ago

Sources

NVD entry for CVE-2025-66376 nvd.nist.gov/vuln/detail/CVE-2025-66376
CISA Known Exploited Vulnerabilities catalog www.cisa.gov/known-exploited-vulnerabilities-catalog
wiki.zimbra.com wiki.zimbra.com/wiki/Zimbra_Security_Advisories
nvd.nist.gov nvd.nist.gov/vuln/detail/CVE-2025-66376