CVE-2025-27915
Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
IN CISA KEV
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.
- Vendor
- Synacor
- Product
- Zimbra Collaboration Suite (ZCS)
- CVSS
- No score recorded (no NVD record loaded for this entry)
- CWE
- CWE-79
- Published
- Not recorded
- NVD modified
- Not recorded
CISA KEV
- Date added
- 2025-10-07
- Due date
- 2025-10-28
- Ransomware use
- Unknown
- 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.
EPSS
4.06% chance of exploitation in the next 30 days (percentile 90th)
FIRST EPSS, updated 17 Oct 2026. About EPSS
CVSS is severity, EPSS is likelihood, KEV means already exploited. EPSS is a statistical probability, not a certainty: a low score does not make a bug safe, and a high one does not prove it is being exploited.
Data last updated 18 Oct 2026. Sources: NVD API 2.0, CISA KEV catalog, FIRST EPSS. Links: NVD, CISA KEV. Metadata only. ThreatWire does not host exploit code.