CVE-2025-27915

MEDIUM5.4

CISA KEV

Published 2025-03-12 · Updated 2026-06-17 · Source cve@mitre.org

Summary

CVE-2025-27915 is a medium-severity (CVSS 5.4) vulnerability in Synacor Zimbra Collaboration Suite (ZCS). CISA added it to the Known Exploited Vulnerabilities catalog on October 7, 2025, which means exploitation in the wild has been confirmed; US federal agencies had to remediate it by October 28, 2025. CISA does not currently list it as used in ransomware campaigns. Synacor has 19 vulnerabilities in the KEV catalog, 6 of them linked to ransomware.

All 19 known-exploited Synacor vulnerabilities →

Description

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 vector: CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N

CWE-79

CISA Known-Exploited Vulnerability

Product: Synacor — Zimbra Collaboration Suite (ZCS)

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

Date added: 2025-10-07 · 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.

References

View on NVD

More exploited Synacor vulnerabilities

Most recently added to CISA KEV

CVE-2026-73570
Zimbra Collaboration Suite (ZCS) — Zimbra Collaboration Suite (ZCS) OS Command Injection Vulnerability
added 2026-08-21
CVE-2025-48700
Zimbra Collaboration Suite (ZCS) — Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability
added 2026-04-20
CVE-2025-66376
Zimbra Collaboration Suite (ZCS) — Synacor Zimbra Collaboration Suite (ZCS) Cross-Site Scripting Vulnerability
added 2026-03-18
CVE-2020-7796
Zimbra Collaboration Suite — Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery Vulnerability
added 2026-02-17
CVE-2025-68645
Zimbra Collaboration Suite (ZCS) — Synacor Zimbra Collaboration Suite (ZCS) PHP Remote File Inclusion Vulnerability
added 2026-01-22
CVE-2019-9621
Zimbra Collaboration Suite (ZCS) — Synacor Zimbra Collaboration Suite (ZCS) Server-Side Request Forgery (SSRF) Vulnerability
added 2025-07-07

View all →

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