October 7, 2025 · Applied Cybernetics Group
CVE-2025-27915 — Synacor Zimbra Collaboration Suite (ZCS)
Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
- Added to KEV
2025-10-07- Federal due date
2025-10-28- Vendor
- Synacor
- Product
- Zimbra Collaboration Suite (ZCS)
- EPSS
- 96.4th percentile (score 0.261, as of
2026-06-08) - NVD CVSS v3.1
- —
- Ransomware use
- Unknown
- Upstream
- https://nvd.nist.gov/vuln/detail/CVE-2025-27915
CISA short description
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.
Required action
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.