# CVE-2026-21857: Redaxo has Path Traversal in Backup Addon Leading to Arbitrary File Read

> Authenticated users with backup permissions can read arbitrary files within the webroot via path traversal in the Redaxo Backup addon.

- **Severity:** High 8.3 (`CVSS:4.0/AV:N/AC:L/AT:N/PR:H/UI:N/VC:H/VI:N/VA:N/SC:H/SI:H/SA:N`)
- **Exploited in the wild:** Not known
- **Login needed:** An administrator
- **Attackable:** Over the internet
- **Victim action needed:** Not needed
- **Fix available:** Yes
- **Published:** 7 Jan 2026
- **Updated:** 8 Jan 2026
- **Also known as:** GHSA-824x-88xg-cwrv

## What is CVE-2026-21857?

CVE-2026-21857 is a high-severity path traversal vulnerability in redaxo, published on 7 Jan 2026. An attacker needs administrator access to exploit it, with no action from the victim.

### Official description

REDAXO is a PHP-based content management system. Prior to version 5.20.2, authenticated users with backup permissions can read arbitrary files within the webroot via path traversal in the Backup addon's file export functionality. The Backup addon does not validate the `EXPDIR` POST parameter against the UI-generated allowlist of permitted directories. An attacker can supply relative paths containing `../` sequences (or even absolute paths inside the document root) to include any readable file in the generated `.tar.gz` archive. Version 5.20.2 fixes this issue.

Weakness: CWE-24 (Path Traversal: '../filedir'), CWE-22 (Improper Limitation of a Pathname to a Restricted Directory)

## Which versions are affected by CVE-2026-21857?

2 open source packages ship an affected version, including redaxo/source. It affects 1 product.


| Package | Ecosystem | Affected | Fixed in |
| --- | --- | --- | --- |
| `redaxo/source` | Packagist | All versions | 5.20.2 |
| `redaxo/source` | Packagist | All versions | 5.20.2 |

Products: Redaxo Redaxo.

## How do I fix CVE-2026-21857?

Upgrade redaxo/source to 5.20.2 or later.

## Is CVE-2026-21857 being exploited?

It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21857 exists.

Public exploit code:

- CVE-2026-21857 - Redaxo has Path Traversal in Backup Addon Leading to Arbitrary File Read (github_poc): https://github.com/lukasz-rybak/CVE-2026-21857

## Other vulnerabilities in redaxo

- [CVE-2018-18200](https://insights.sbomify.com/CVE-2018-18200/): SQL injection in n/a (critical 9.8)
- [CVE-2018-17831](https://insights.sbomify.com/CVE-2018-17831/): SQL injection in n/a (critical 9.8)
- [CVE-2006-2843](https://insights.sbomify.com/CVE-2006-2843/): Code injection in n/a (high 7.5)
- [CVE-2006-2844](https://insights.sbomify.com/CVE-2006-2844/): Multiple PHP remote file inclusion vulnerabilities in Redaxo 3.0 allow remote attackers to execute arbitrary PHP code via a URL in the REX[I (high 7.5)
- [CVE-2006-2845](https://insights.sbomify.com/CVE-2006-2845/): Code injection in n/a (high 7.5)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-21857 and fix it if it is affected.

What it is: CVE-2026-21857 is a high-severity path traversal vulnerability in redaxo, published on 7 Jan 2026. An attacker needs administrator access to exploit it, with no action from the victim.
Exploitation: It is not confirmed as exploited in the wild, but public exploit code for CVE-2026-21857 exists.

Affected packages and fixed versions:
- redaxo/source (Packagist): affected all versions; fixed in 5.20.2
- redaxo/source (Packagist): affected all versions; fixed in 5.20.2

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-2026-21857/ (Markdown: https://insights.sbomify.com/CVE-2026-21857/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-21857
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-21857
- OSV: https://osv.dev/vulnerability/CVE-2026-21857

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-21857/
Summaries are generated and may contain mistakes; the official description above is the record.