CISA KEV · Known exploitedMedium

CVE-2025-27915

Synacor Zimbra Collaboration Suite (ZCS)

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,...

CVSS: 5.4
EPSS: 4.34%
CISA KEV: Listed
Published: 2025.03.13

PRIORITY ASSESSMENT

Immediate review

CISA has listed this vulnerability in the Known Exploited Vulnerabilities catalog.

Known exploitationConfirmed by CISA KEV

Exploit probability4.34%

Technical severityCVSS 5.4

Vulnerability overview

Affected product and versions

Product: Synacor Zimbra Collaboration Suite (ZCS)
Affected versions: >= 10.0.0 < 10.0.13, >= 10.1.0 < 10.1.5, 9.0.0
Fixed versions: 10.0.13, 10.1.5

Recommended response sequence

Confirm exposure before applying a vendor-supported change.

Full remediation guide

CISA 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.

Due date: 2025.10.28

1
Identify
Confirm that Synacor Zimbra Collaboration Suite (ZCS) and an affected version are present.
2
Prioritize
Combine exploitation signals with asset exposure and business criticality.
3
Remediate
Follow the vendor advisory or supported update path and preserve rollback options.
4
Verify
Recheck the version, service health, access paths, and relevant logs.

Technical data

CVSS vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N
CWE: CWE-79
KEV added: 2025.10.07
Ransomware use: 미확인