CVE DATABASE / CVE-2025-27915

CVE-2025-27915

Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability

CVSS 5.4 · MEDIUM ⚠ CISA KEV — ACTIVELY EXPLOITED

On the CISA KEV catalog

Confirmed exploited in the wild. Added 2025-10-07. Federal remediation due 2025-10-28.
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.

Summary

An issue was discovered in Zimbra Collaboration (ZCS) 9.0 and 10.0 and 10.1. A stored cross-site scripting (XSS) vulnerability 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 <details> 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.

CVSS 3.1 breakdown

Base score	5.4 (MEDIUM)
Vector	CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
Attack vector	NETWORK
Attack complexity	LOW
Privileges required	LOW
User interaction	REQUIRED
Scope	CHANGED
Confidentiality	LOW
Integrity	LOW
Availability	NONE

Weakness type (CWE)

CWE-79

Affected products

Synacor zimbra collaboration suite

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References

Data: NIST NVD + CISA KEV. NVD last modified 2025-11-04. Always verify against the vendor advisory before acting.