Contao: Cross-site scripting in the comments bundle
An unauthenticated front end visitor can post a comment containing an XSS injection. The victim is any back end user who opens the Comments module, and moderation makes exposure certain rather than preventing it. No Content-Security-Policy header is sent on the Contao back end, so nothing mitigates the inline handler.
Impact
Anyone on the internet can inject script that executes in the Contao back end origin, under the session of whichever user opens the Comments module, with no click and no hover. From there the payload acts as that user through the back end: reading any module they can reach, creating a new administrator, or editing a template, which on Contao is a documented path from back end write access to code execution. Moderation does not help and in fact guarantees exposure, since unpublished comments are still inserted and a moderator has to open the list to act on them.
What to do
Update contao/comments-bundle to version 5.3.50, 5.7.12, or later.
Affected software
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| Platform | Package | Vulnerable versions | Fixed in |
|---|---|---|---|
| Composer package | contao/comments-bundle | >= 4.0.0, < 5.3.50, >= 5.4.0-RC1, < 5.7.12 | 5.3.50, 5.7.12 |
References
- CVSS vector
CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N- Weakness (CWE)
CWE-116, CWE-79- Platform
- Composer
- Package
contao/comments-bundle- Disclosed
- 09.10.2026
- Updated
- 11.10.2026 10:32
Sources and licenses · Edited or translated by DockRay; source rights and applicable licenses are retained.
OSV / GitHub Advisory Database - GHSA-628f-v4f6-p37r - CC BY 4.0
Vulnerability history: contao/comments-bundle
All published vulnerabilities of this package (Composer package), newest first. Shows whether this is a one-off slip or a package that needs watching.
- Total entries
- 2
- First → latest
- 04.2024 10.2026
- Without a fix
- 0
- Exploited in attacks
- 0
Severity breakdown
- Critical 1
- Medium 1
Disclosures per year
- 2024: 1
- 2025: 0
- 2026: 1
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Contao: Cross-site scripting in the comments bundle this entry
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