Synacor Zimbra Collaboration up to 10.1.20 Classic UI cross site scripting

Summaryinfo

A vulnerability described as problematic has been identified in Synacor Zimbra Collaboration up to 10.1.20. The affected element is an unknown function of the component Classic UI. Executing a manipulation can lead to cross site scripting. This vulnerability is handled as CVE-2026-66912. The attack can be executed remotely. There is not any exploit available. Upgrading the affected component is recommended.

Detailsinfo

A vulnerability has been found in Synacor Zimbra Collaboration up to 10.1.20 and classified as problematic. This vulnerability affects an unknown code block of the component Classic UI. The manipulation with an unknown input leads to a cross site scripting vulnerability. The CWE definition for the vulnerability is CWE-79. The product does not neutralize or incorrectly neutralizes user-controllable input before it is placed in output that is used as a web page that is served to other users. As an impact it is known to affect integrity. CVE summarizes:

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. This issue was fixed in version 10.1.21

The advisory is available at cert.pl. This vulnerability was named CVE-2026-66912 since 07/28/2026. The exploitation appears to be easy. The attack can be initiated remotely. Successful exploitation requires user interaction by the victim. The technical details are unknown and an exploit is not available. This vulnerability is assigned to T1059.007 by the MITRE ATT&CK project.

Upgrading to version 10.1.21 eliminates this vulnerability.

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Productinfo

Type

• Groupware Software

Vendor

• Synacor

Name

• Zimbra Collaboration

Version

• 10.1.0
• 10.1.1
• 10.1.2
• 10.1.3
• 10.1.4
• 10.1.5
• 10.1.6
• 10.1.7
• 10.1.8
• 10.1.9
• 10.1.10
• 10.1.11
• 10.1.12
• 10.1.13
• 10.1.14
• 10.1.15
• 10.1.16
• 10.1.17
• 10.1.18
• 10.1.19
• 10.1.20

License

• free

Website

• Vendor: https://synacor.com/

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