Kimai has Stored XSS via Incomplete HTML Attribute Escaping in Team Member Widget

Summary

The client-side escapeForHtml() function in KimaiEscape.js, introduced in commit 89bfa82c (#2959) to fix a JavaScript XSS vulnerability, only escapes <, >, and & but does not escape " (double quote) or ' (single quote). When user-controlled data (profile alias) is placed in an HTML attribute context (title="__DISPLAY__") via the team member form prototype and rendered through innerHTML, the missing quote escaping allows HTML attribute injection, resulting in Stored XSS.

Details

Incomplete security patch. The escapeForHtml() function was meant to prevent XSS but missed quote characters, which are critical for HTML attribute context escaping.

Vulnerable code — assets/js/plugins/KimaiEscape.js:29-33:

const tagsToReplace = {
    '&': '&',
    '<': '&lt;',
    '>': '&gt;',
    // MISSING: '"': '&quot;'
    // MISSING: "'": '&#039;'
};

Affected code files:

• assets/js/plugins/KimaiEscape.js:24-38 — incomplete escape function
• assets/js/forms/KimaiTeamForm.js:77,86 — replacement + innerHTML
• templates/macros/widgets.html.twig:126 — title="{{ tooltip }}" in avatar macro
• templates/form/blocks.html.twig:104 — {{ widgets.avatar('__INITIALS__', '__COLOR__', '__DISPLAY__') }}

PoC

poc.zip

Please extract the uploaded compressed file before proceeding

1. ./setup.sh
2. ./poc_xss.sh

Impact

• Stored XSS: payload persists in the database (user alias field)
• Privilege escalation: ROLE_USER injects XSS that executes in ROLE_ADMIN/ROLE_SUPER_ADMIN browser session