CVE-2025-27915
Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
CVSS
—
No CVSS
EPSS
4.1%
p91
KEV
YES
Oct 7, 2025
Exploit Today
77
0-100
Published: — · Last modified: —
Product
Synacor / Zimbra Collaboration Suite (ZCS)
Vulnerability
Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
Added to KEV
Oct 7, 2025
Remediate by
Oct 28, 2025
Known ransomware use
No
Summary 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.
Notes
https://wiki.zimbra.com/wiki/Security_Center ; https://nvd.nist.gov/vuln/detail/CVE-2025-27915