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

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• NewsExploited · CISA KEVSynacor · Zimbra Collaboration Suite (ZCS)

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

  CVE-2025-66376

  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.

  CISA's required action · due 1 Apr 2026 for U.S. federal civilian agencies

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

  Cited by CISA: wiki.zimbra.com · nvd.nist.gov

  Added to KEV 18 Mar 2026 · Source checked 4 Nov 2026, 16:35 UTC · CISA KEV entry

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