Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting
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 2025-10-28 · passed 10 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 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.
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
- Added to CISA KEVExploitation in the wild confirmed by CISA
- CISA remediation deadlinepassed 10 months ago
Sources
- NVD entry for CVE-2025-27915 nvd.nist.gov/vuln/detail/CVE-2025-27915
- CISA Known Exploited Vulnerabilities catalog www.cisa.gov/known-exploited-vulnerabilities-catalog
- wiki.zimbra.com wiki.zimbra.com/wiki/Security_Center
- nvd.nist.gov nvd.nist.gov/vuln/detail/CVE-2025-27915