CVE-2025-27915 — Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
CVE-2025-27915: Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
CISA Known Exploited Vulnerability (KEV)
| Vendor / project | Synacor |
| Product | Zimbra Collaboration Suite (ZCS) |
| Date added | 2025-10-07 |
| Due date | 2025-10-28 |
| Ransomware campaign use | Unknown |
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 (CISA)
Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.
Notes
https://wiki.zimbra.com/wiki/Security_Center ; https://nvd.nist.gov/vuln/detail/CVE-2025-27915
References
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2025-27915
- KEV catalog: https://www.cisa.gov/known-exploited-vulnerabilities-catalog