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CVE-2025-27915: Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability

Synacor Zimbra Collaboration Suite (ZCS) · in CISA KEV since 2025-10-07

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2025-10-07added to KEV

2025-10-28federal remediation due date

3.99%EPSS exploit probability (30 days) 90.2th percentile

5.4 MEDIUMCVSS 3.1

Unknownknown ransomware use

209days from NVD publication to KEV

What it is

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 (CISA)

Apply mitigations per vendor instructions, follow applicable BOD 22-01 guidance for cloud services, or discontinue use of the product if mitigations are unavailable.

CWE	CWE-79
CVSS vector	`CVSS:3.1/AV:N/AC:L/PR:L/UI:R/S:C/C:L/I:L/A:N`
NVD published	2025-03-12 (Analyzed)

Original records: NVD · CISA KEV · JSON: /api/cve/CVE-2025-27915.json · all KEV CVEs

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