CVE-2026-40479 is a medium-severity (CVSS 5.4) Cross-site Scripting (XSS) vulnerability in kimai/kimai. A fix is available for kimai/kimai — see the affected versions and patch details below.
Kimai: Stored XSS via Incomplete HTML Attribute Escaping in Team Member Widget
Exploitation Status
Proof-of-concept exploit code exists
- CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.
Exploitation and automatability from CISA’s SSVC triage for CVE-2026-40479.
EPSS Exploitation Probability
Probability of exploitation in the next 30 days, from FIRST.org EPSS.
How urgent is this, really
Where this sits among everything scored
Real-World Exposure
kimai/kimaiReal-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.
Description
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 = {
'&': '&',
'<': '<',
'>': '>',
// MISSING: '"': '"'
// MISSING: "'": '''
};
Affected code files:
assets/js/plugins/KimaiEscape.js:24-38— incomplete escape functionassets/js/forms/KimaiTeamForm.js:77,86— replacement + innerHTMLtemplates/macros/widgets.html.twig:126—title="{{ tooltip }}"in avatar macrotemplates/form/blocks.html.twig:104—{{ widgets.avatar('__INITIALS__', '__COLOR__', '__DISPLAY__') }}
PoC
Please extract the uploaded compressed file before proceeding
- ./setup.sh
- ./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
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | kimai/kimai | all versions | 2.53.0composer require kimai/kimai:^2.53.0 |
Affected Products
kimaikimaiDetection & mitigation playbook
Open-source dependencyDetect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for kimai/kimai, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update kimai/kimai to 2.53.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-40479 is resolved across your whole dependency graph.
Workarounds
Escape or sanitise the affected output on the server side rather than relying on client-side filtering, and add a Content-Security-Policy that blocks inline script execution so injected markup cannot run even if it reaches the page.
Frequently Asked Questions
Is CVE-2026-40479 in your dependencies?
Find it across Packagist, including transitive dependencies.