CVE-2025-48700: Synacor Zimbra Collaboration Suite (ZCS) Cross-site Scripting Vulnerability

Synacor Zimbra Collaboration Suite contains a cross-site scripting vulnerability tracked as CVE-2025-48700. The flaw falls under CWE-79 and can allow an attacker to execute arbitrary JavaScript inside an authenticated user's browser session, which may expose session tokens or other sensitive data visible to that user.

How it works

CWE-79 describes improper neutralization of input during web page generation. In this class of weakness an attacker supplies data that the application later renders without adequate escaping, so the browser interprets the data as executable script rather than plain text.

• The injected script runs with the privileges of the logged-in user and can read or manipulate page content visible in that session.
• Attackers commonly deliver the payload through application features that accept and redisplay user-controlled content.
• Successful execution can lead to unauthorized access to information stored or displayed within the Zimbra interface.

Am I affected? How to find it in your systems

Synacor Zimbra Collaboration Suite is an on-premises or hosted email and groupware platform. Inventory all internet-facing and internal instances by checking DNS records, load-balancer configurations, and server inventories for Zimbra services.

• Confirm the installed build version of ZCS against the vendor advisory to determine whether the instance is within the affected range.
• Review web-application firewall or proxy logs for requests containing unusual script tags, event handlers, or encoded JavaScript in parameters that Zimbra renders back to users.
• Examine authentication and session logs for unexpected redirects or content changes that coincide with user activity.

How to remediate

Apply the vendor-supplied update referenced in the official advisory. After patching, review the application's handling of user-supplied content and ensure standard output-encoding practices are in place for all rendered fields.

• Validate that input sanitization covers the specific entry points identified by the vendor.
• Enable any built-in security headers or content-security-policy settings that Zimbra supports.
• Re-test the application with automated and manual XSS test cases once the update is deployed.

If you can't patch immediately

Until the update can be applied, reduce exposure through network and application controls.

• Restrict direct access to Zimbra web interfaces to trusted networks or require VPN connectivity.
• Deploy or tune web-application firewall rules that block or sanitize common XSS patterns targeting the affected endpoints.
• Disable non-essential collaboration features that accept and display rich content if the configuration permits.
• Monitor authentication logs and user-session activity for anomalies that could indicate successful script execution.

If your data may have been exposed

Cross-site scripting flaws that are actively exploited can result in account compromise and subsequent data exposure. Organizations can run a free exposure scan of their email addresses against known breach datasets to check for signs of prior credential leakage.