What is CVE-2026-21857?

### Summary Authenticated users with backup permissions can read arbitrary files within the webroot via path traversal in the Backup addon's file export functionality. ### Details The Backup addon does not validate the `EXPDIR` POST parameter against the UI-generated allowlist of permitted directories. An attacker can supply relati

How severe is CVE-2026-21857?

No CVSS score has been assigned to CVE-2026-21857 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-21857?

CVE-2026-21857 affects the following packages: redaxo/source (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2026-21857?

Update redaxo/source to 5.20.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-21857 is resolved across your whole dependency graph.

How do I detect CVE-2026-21857 in my Packagist dependencies?

Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for redaxo/source, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.

How do I mitigate CVE-2026-21857 if there is no patch (or I can't update yet)?

Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Is CVE-2026-21857 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-21857 yet. This does not mean the vulnerability cannot be exploited — absence of public exploits does not imply safety. Apply the recommended fix and use O3 Security to monitor your exposure.

What is the EPSS score for CVE-2026-21857?

CVE-2026-21857 has an EPSS (Exploit Prediction Scoring System) score of 0.5%, placing it in the 45th percentile of all CVEs. EPSS is maintained by FIRST.org and estimates the probability that a vulnerability will be exploited in the wild within the next 30 days. This score indicates relatively lower exploitation probability, though the CVSS severity should still guide your patching priority.

What type of vulnerability is CVE-2026-21857?

CVE-2026-21857 is classified as Path Traversal (CWE-22), CWE-24 (CWE-24). These weakness types describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation. This is a high-impact weakness class that often enables remote code execution or data exposure.

When was CVE-2026-21857 published, and has it been updated?

CVE-2026-21857 was published on January 7, 2026 and was last updated on October 28, 2026. Advisory data evolves as severity scores, affected ranges, and exploit intelligence are revised — always check the latest version of the advisory before acting.

🐘 Packagist

Not in CISA KEV

CVE-2026-21857 — source

CVE-2026-21857 is a Path Traversal vulnerability in redaxo/source. A fix is available for redaxo/source — see the affected versions and patch details below.

Redaxo has Path Traversal in Backup Addon Leading to Arbitrary File Read

Also known asGHSA-824x-88xg-cwrv

Published

Jan 7, 2026

Updated

Oct 28, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Nov 2, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

Proof-of-concept exploit code exists

CISA’s SSVC triage found public proof-of-concept exploit code for this CVE, though no confirmed active exploitation.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-21857.

EPSS Exploitation Probability

via FIRST.org ↗

0.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs45th percentile — riskier than 45% of all scored CVEsHighest risk

Probability of exploitation in the next 30 days, from FIRST.org EPSS.

Real-World Exposure

1 pkg affected

🐘redaxo/source

Real-time download stats are indexed for npm and PyPI packages. This vulnerability affects Packagist packages — download data is not available via public APIs for these ecosystems.

Description

Summary

Authenticated users with backup permissions can read arbitrary files within the webroot via path traversal in the Backup addon's file export functionality. <img width="664" height="899" alt="image" src="https://github.com/user-attachments/assets/fd1ca69e-b275-4daf-9a62-621cde6525f5" /> <img width="2358" height="445" alt="image" src="https://github.com/user-attachments/assets/fad81152-9e1b-413e-9823-09540a23e2fb" />

Details

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.

Vulnerable code:

redaxo/src/addons/backup/pages/export.php (lines 72-76) – directly uses $_POST['EXPDIR']
redaxo/src/addons/backup/lib/backup.php (lines ~413 & ~427) – concatenates unsanitized user input with base path

This allows disclosure of sensitive files such as:

redaxo/data/core/config.yml → database credentials + password hashes of all backend users
.env, custom configuration files, logs, uploaded malicious files, etc.

Affected versions

≤ 5.20.1 (confirmed working)

Patched versions

None (as of 2025-12-09)

PoC – Extracting database credentials and password hashes

Log in as any user with Backup permission
Go to Backup → Export → Files

Intercept the request with Burp Suite

Change one EXPDIR[] value to ../../../../var/www/html/redaxo/data/core

Send request → download archive
<img width="423" height="131" alt="image" src="https://github.com/user-attachments/assets/db8a8bda-cdaf-4dea-812f-1e312da908e2" />
Extract and open data/core/config.yml
<img width="859" height="281" alt="image" src="https://github.com/user-attachments/assets/c8112ce1-5a1d-435f-953b-7eb4e711e042" />

Result: plaintext database password <img width="2534" height="1198" alt="image" src="https://github.com/user-attachments/assets/218ae917-868a-437e-98b0-6471b82c0b10" />

Impact

Full compromise of the REDAXO installation:

Database takeover
Password hash extraction → offline cracking → admin access
When combined with other vulnerabilities → RCE

CVSS 4.0 vector & score below.

Credits

Discovered by: Łukasz Rybak

Affected Packages

1 total 1 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`redaxo/source`	all versions	5.20.2`composer require redaxo/source:^5.20.2`

Affected Products

1 product · 1 configurations

Application

redaxoredaxo

< 5.20.2

range

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for redaxo/source, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update redaxo/source to 5.20.2 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-21857 is resolved across your whole dependency graph.
Workarounds
Resolve every user-supplied path to its canonical form and reject anything that escapes the intended directory, and run the component under an account that has no read or write access outside the directory it legitimately serves.

Frequently Asked Questions

### Summary Authenticated users with backup permissions can read arbitrary files within the webroot via path traversal in the Backup addon's file export functionality. <img width="664" height="899" alt="image" src="https://github.com/user-attachments/assets/fd1ca69e-b275-4daf-9a62-621cde6525f5" /> <img width="2358" height="445" alt="image" src="https://github.com/user-attachments/assets/fad81152-9e1b-413e-9823-09540a23e2fb" /> ### Details The Backup addon does not validate the `EXPDIR` POST parameter against the UI-generated allowlist of permitted directories. An attacker can supply relati