Stored XSS in HumHub Comment Deletion Notification

Executive Summary

HumHub 1.18.4 has a stored cross-site scripting (XSS) vulnerability in the comment-deletion notification system. A Space administrator can delete another user's comment and insert malicious HTML or JavaScript into the deletion reason. When the notification is viewed by the original comment author, the script executes in their authenticated session, allowing unauthorized actions.

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Detection Guidance

To detect this vulnerability, inspect HumHub comment deletion notifications for suspicious HTML/JavaScript in deletion reasons. Check notification dropdowns for unexpected script execution. Review server logs for unauthorized administrative actions following comment deletions. Ensure HumHub is updated to a patched version.

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Impact Analysis

An attacker with Space administrator privileges could inject malicious scripts via comment deletion reasons. When a victim views the notification, the script runs in their browser session, potentially allowing the attacker to change passwords, take over accounts, or perform other unauthorized actions within the victim's session.

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Compliance Impact

This vulnerability could lead to unauthorized access or data breaches, violating confidentiality requirements under GDPR and HIPAA. It undermines access controls and could result in unauthorized data exposure or modification, posing significant compliance risks.

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Mitigation Strategies

Immediately update HumHub to the latest patched version to address the XSS flaw. Restrict Space administrator privileges to trusted users only. Monitor notification systems for unusual activity. Disable HTML rendering in deletion reasons if possible until patched.

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