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

> An unauthenticated attacker can inject scripts via comment metadata that execute in the backend when moderators view comments, potentially leading to session hijacking.

- **Severity:** Critical 9.3 (`CVSS:3.1/AV:N/AC:L/PR:N/UI:R/S:C/C:H/I:H/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Over the internet
- **Victim action needed:** A user has to click or open something
- **Fix available:** Yes
- **Published:** 9 Oct 2026
- **Updated:** 9 Oct 2026
- **Also known as:** GHSA-628f-v4f6-p37r

## What is CVE-2026-107845?

CVE-2026-107845 is a critical cross-site scripting vulnerability in contao, published on 9 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.

### Official 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 Unpublished comments remain visible to moderators, so moderation does not prevent exposure.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.

Weakness: CWE-79 (Improper Neutralization of Input During Web Page Generation), CWE-116 (Improper Encoding or Escaping of Output)

## Which versions are affected by CVE-2026-107845?

4 open source packages ship an affected version, including contao/comments-bundle.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `contao/comments-bundle` | Packagist | From 4.0.0 | 5.3.50 |
| `contao/comments-bundle` | Packagist | From 4.0.0 | 5.3.50 |
| `contao/comments-bundle` | Packagist | From 5.4.0-RC1 | 5.7.12 |
| `contao/comments-bundle` | Packagist | From 5.4.0-RC1 | 5.7.12 |

## How do I fix CVE-2026-107845?

Upgrade contao/comments-bundle to a fixed version for your release line: 5.3.50 or 5.7.12.

## Is CVE-2026-107845 being exploited?

There is no known exploitation of CVE-2026-107845 in the wild and no public exploit code.

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-107845 and fix it if it is affected.

What it is: CVE-2026-107845 is a critical cross-site scripting vulnerability in contao, published on 9 Oct 2026. An attacker can exploit it over the internet without logging in, and only if a user opens a file or follows a link.
Exploitation: There is no known exploitation of CVE-2026-107845 in the wild and no public exploit code.

Affected packages and fixed versions:
- contao/comments-bundle (Packagist): affected from 4.0.0; fixed in 5.3.50
- contao/comments-bundle (Packagist): affected from 4.0.0; fixed in 5.3.50
- contao/comments-bundle (Packagist): affected from 5.4.0-RC1; fixed in 5.7.12
- contao/comments-bundle (Packagist): affected from 5.4.0-RC1; fixed in 5.7.12

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-107845/ (Markdown: https://insights.sbomify.com/CVE-2026-107845/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-107845
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-107845
- OSV: https://osv.dev/vulnerability/CVE-2026-107845

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-107845/
Summaries are generated and may contain mistakes; the official description above is the record.