# REDAXO reflected XSS in backend packages API

Source: https://junglewise.ai/threats/redaxo-reflected-xss-in-backend-packages-api-9ebf14f6  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-04-10. Updated: 2026-05-10  
License: CC BY 4.0 with a link back

Severity: low · CVSS 2.1 · Published 2026-04-10

REDAXO is a content management system used to build and manage websites. A security flaw in its administrative backend allows malicious code to be reflected back to a user through the packages API. While an exploit requires high-level administrative access and a valid security token, it could allow an attacker to perform unauthorized actions or view sensitive data within the management interface.

Technologies: [redaxo/source (Packagist)](https://junglewise.ai/threats/technologies/redaxo-source), [REDAXO](https://junglewise.ai/threats/technologies/redaxo). Vendors: [Packagist](https://junglewise.ai/threats/vendors/packagist), [REDAXO](https://junglewise.ai/threats/vendors/redaxo).

## Quick answers

**Is This vulnerability exploited in the wild?** No. Junglewise Threat Intelligence has no report of This vulnerability being exploited in the wild.

**How severe is This vulnerability?** Low severity, with a CVSS score of 2.1, published 10 April 2026.

**Which products and versions are affected?** redaxo/source (Packagist) < 5.21.0; REDAXO < 5.21.0.

**Is there a fix for This vulnerability?** A patch was published on 2026-04-09: Release 5.21.0 published. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is This vulnerability attacked?** It is attacked over the network, in a web application.

**Am I affected?** Check whether you run redaxo/source (Packagist) or REDAXO at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## Technical details

A reflected Cross-Site Scripting (XSS) vulnerability exists in the REDAXO backend packages API. The root cause is the lack of HTML escaping when the 'function' GET parameter is concatenated into an exception message in 'redaxo/src/core/lib/packages/api_package.php' and subsequently rendered via 'rex_view::error()'. An attacker with high privileges (backend session) can inject arbitrary JavaScript. However, exploitation is mitigated by the requirement of a valid CSRF token ('_csrf_token') for the API call. The vulnerability is patched in version 5.21.0.

## Affected products

- REDAXO core < 5.21.0

## Timeline

- 2026-04-09: patched: Release 5.21.0 published.
- 2026-04-10: advisory: GitHub Advisory GHSA-xq4j-g85q-wf97 published.

## References

- [https://api.github.com/users/NumberOreo1](https://api.github.com/users/NumberOreo1)
- [https://github.com/NumberOreo1](https://github.com/NumberOreo1)
- [https://api.github.com/users/NumberOreo1/gists%7B/gist_id%7D](https://api.github.com/users/NumberOreo1/gists%7B/gist_id%7D)
- [https://api.github.com/users/NumberOreo1/repos](https://api.github.com/users/NumberOreo1/repos)
- [https://avatars.githubusercontent.com/u/122526229?v=4](https://avatars.githubusercontent.com/u/122526229?v=4)
- [https://api.github.com/users/NumberOreo1/events%7B/privacy%7D](https://api.github.com/users/NumberOreo1/events%7B/privacy%7D)

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