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Exploited vulnerability

CVE-2025-27915

TLP:CLEAR

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

Synacor Zimbra Collaboration Suite (ZCS) contains a cross-site scripting vulnerability that exists in the Classic Web Client due to insufficient sanitization of HTML content in ICS files. When a user views an e-mail message containing a malicious ICS entry, its embedded JavaScript executes via an ontoggle event inside a tag. This allows an attacker to run arbitrary JavaScript within the victim's session, potentially leading to unauthorized actions such as setting e-mail filters to redirect messages to an attacker-controlled address. As a result, an attacker can perform unauthorized actions on the victim's account, including e-mail redirection and data exfiltration.

Facts

  • Vendor: Synacor
  • Product: Zimbra Collaboration Suite (ZCS)
  • CVSS: 5.4
  • EPSS (probability of exploitation within 30 days): 4.1 %
  • On CISA's Known Exploited Vulnerabilities list since: 7 October 2025
  • First known exploitation: 7 October 2025
  • CISA's deadline for US federal agencies: 28 October 2025
  • Weakness: CWE-79
  • First seen by Risk Letters: 7 October 2025

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

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