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)?

If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.

How does O3 Security protect against CVE-2026-21857?

O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-21857 can be triaged on real exposure rather than presence alone.

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 44th 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 August 22, 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 — redaxo/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

Aug 22, 2026

Affected

1 pkg

Patched

1 / 1

Exploits

None indexed

Exploitation data as of Sep 18, 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 CVEs44th percentile — riskier than 44% of all scored CVEsHighest risk

EPSS (Exploit Prediction Scoring System) is a daily probability model maintained by FIRST.org. It estimates the likelihood a CVE will be exploited in production environments within the next 30 days, derived from real-world threat intelligence signals.

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

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.

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`

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
If you can't upgrade right away: gate or disable the affected feature, validate untrusted input at the boundary, and avoid passing attacker-controlled data into the vulnerable path. O3's runtime protection blocks exploitation in production as an interim safeguard until the upgrade lands.
How O3 protects you
O3 Security's impact-aware SCA analyses which vulnerable code paths your application actually calls, so a match like CVE-2026-21857 can be triaged on real exposure rather than presence alone.

Tailored to CVE-2026-21857. Runtime protection reduces exposure until a permanent patch is applied and verified — it complements patching, it doesn't replace it.

Frequently Asked Questions

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.

O3 Security · Impact-Aware SCA

Is CVE-2026-21857 in your dependencies?

O3 Security finds CVE-2026-21857 across Packagist dependencies, including transitive ones, and its impact-aware SCA ranks findings by whether your code actually calls the vulnerable path.

Scan my dependencies How O3 SCA works