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

Exploited in the wild Medium 5.4 Published 12 Mar 2025 Updated 26 Feb 2026

Stored XSS in Zimbra allows attackers to execute JavaScript via malicious ICS files, enabling account takeover and data exfiltration.

Exploited in the wild: Since 7 Oct 2025
Login needed: Any signed-in user
Attackable: Over the internet
Victim action needed: A user has to click or open something
Fix: None listed

What is CVE-2025-27915?

CVE-2025-27915 is a medium-severity cross-site scripting vulnerability in Synacor Zimbra Collaboration Suite, published on 12 Mar 2025. Any signed-in user can exploit it over the network, and only if a user opens a file or follows a link.

Official 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.

Weakness: CWE-79

Which versions are affected by CVE-2025-27915?

It affects 1 product.

Products include Synacor Zimbra Collaboration Suite.

How do I fix CVE-2025-27915?

No fix has been published for CVE-2025-27915 yet. Limit exposure of the affected software until one is available. US federal agencies must fix it by 28 Oct 2025.

Escape output for the context it lands in and set a strict Content Security Policy. Upgrading the affected component is the real fix. More about Cross-site scripting.

Is CVE-2025-27915 being exploited?

Yes. Attackers have exploited CVE-2025-27915 in the wild since at least 7 Oct 2025.

Public exploit code: 1 Nuclei template.

All Synacor Zimbra Collaboration Suite vulnerabilities

Sources

Also known as GHSA-5rg8-g76j-7fw7.