Risk Letters

Exploited vulnerability

CVE-2025-66376

TLP:CLEAR

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

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.

Facts

  • Vendor: Synacor
  • Product: Zimbra Collaboration Suite (ZCS)
  • CVSS: 7.2
  • EPSS (probability of exploitation within 30 days): 20.2 %
  • On CISA's Known Exploited Vulnerabilities list since: 18 March 2026
  • First known exploitation: 18 March 2026
  • CISA's deadline for US federal agencies: 1 April 2026
  • Weakness: CWE-79
  • First seen by Risk Letters: 20 March 2026

Members see which Nordic sectors the flaw hits, and what to do about it.

Get the full brief

Data: NVD (public domain), CISA KEV, FIRST EPSS, MITRE ATT&CK, AlienVault OTX. NVD