Description

CERT Polska employee discovered vulnerabilities in Synacor Zimbra Collaboration software during his own research and participated in coordination of their disclosure.

The vulnerability CVE-2026-66911: Zimbra is vulnerable to stored cross-site scripting (XSS) via the Content-Location MIME header in email attachments. Due to lack of sanitization of the Content-Location header, an attacker can set it to a javascript: URI. An unauthenticated remote attacker can send a crafted email to a victim; when the victim opens the email in the Zimbra web interface and clicks the attachment name, the JavaScript payload executes in the victim's browser context.

The vulnerability CVE-2026-66912: Zimbra is vulnerable to Stored Cross-Site Scripting (XSS) via the From email header during HTML reply composition in Classic UI. Due to insufficient sanitization of the From header value, a remote attacker can send a crafted email containing a malicious From header with an embedded JavaScript payload. When the victim opens the message in Classic UI and clicks Reply while composing in HTML mode with reply headers disabled, the unsanitized From header content is rendered as HTML and the JavaScript payload executes in the victim's browser, potentially allowing the attacker to steal session information or perform actions on behalf of the victim.

These issues were fixed in version 10.1.21

Credits

We thank Suraj Disoja (TrustFoundry), who independently discovered CVE-2026-66911 and responsibly reported it to the vendor.