How severe is CVE-2021-23420?

CVE-2021-23420 has a CVSS score of 9.8/10, rated CRITICAL. Immediate patching is strongly recommended.

Which packages are affected by CVE-2021-23420?

CVE-2021-23420 affects the following packages: codeception/codeception (Packagist), codeception/codeception (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2021-23420?

Update codeception/codeception to 3.1.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23420 is resolved across your whole dependency graph.

How do I detect CVE-2021-23420 in my Packagist dependencies?

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

How do I mitigate CVE-2021-23420 if there is no patch (or I can't update yet)?

Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Is CVE-2021-23420 actively exploited in the wild?

Yes. There are 1 known exploit references for CVE-2021-23420, including 1 in-the-wild exploitation observed on GitHub and other sources. Treat this as actively exploitable and prioritize patching immediately. All exploit code should only be run in an isolated sandbox environment for research or authorized testing — never against production systems without explicit written authorization.

What is the EPSS score for CVE-2021-23420?

CVE-2021-23420 has an EPSS (Exploit Prediction Scoring System) score of 2.7%, placing it in the 86th 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-2021-23420?

CVE-2021-23420 is classified as Deserialization of Untrusted Data (CWE-502). This weakness type 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-2021-23420 published, and has it been updated?

CVE-2021-23420 was published on August 11, 2021 and was last updated on July 9, 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

CRITICAL severity

CVE-2021-23420 — codeception

CRITICALFix: Codeception/Codeception#6241

CVE-2021-23420 is a critical-severity (CVSS 9.8) Deserialization of Untrusted Data vulnerability in codeception/codeception. 1 public exploit reference exists, so weaponization risk is real. A fix is available for codeception/codeception — see the affected versions and patch details below.

Deserialization of Untrusted Data in codeception/codeception

Also known asGHSA-4574-qv3w-fcmg

Published

Aug 11, 2021

Updated

Jul 9, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

1 known

Exploitation data as of Oct 9, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

EPSS Exploitation Probability

via FIRST.org ↗

2.7%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs86th percentile — riskier than 86% of all scored CVEsHighest risk

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

How urgent is this, really

CVE-2021-23420 by exploitation likelihood (EPSS) against impact (CVSS). Outside the shaded patch-first corner.

Where this sits among everything scored

Of 385,738 CVEs with a current EPSS score, this one falls in the < 10% band (highlighted). Counts from FIRST.org, log-scaled.

Real-World Exposure

2 pkgs affected

🐘codeception/codeception🐘codeception/codeception

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

This affects the package codeception/codeception from 4.0.0 and before 4.1.22, before 3.1.3. The RunProcess class can be leveraged as a gadget to run arbitrary commands on a system that is deserializing user input without validation.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`codeception/codeception`	all versions	3.1.3`composer require codeception/codeception:^3.1.3`
🐘Packagist	`codeception/codeception`	≥ 4.0.0&&< 4.1.22	4.1.22`composer require codeception/codeception:^4.1.22`

Affected Products

1 product · 2 configurations

Application

codeceptioncodeception

≥ 4.0.0 && < 4.1.22

range

Exploits & PoCs

Research use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.

This affects the package codeception/codeception from 4.0.0 and before 4…

github.comNVDAug 2021

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for codeception/codeception, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update codeception/codeception to 3.1.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2021-23420 is resolved across your whole dependency graph.
Workarounds
Do not deserialise data from untrusted sources: where the format allows it, restrict deserialisation to an explicit allowlist of expected types, and prefer a data-only format (JSON, Protobuf) over one that can reconstruct arbitrary objects until you can upgrade.

Frequently Asked Questions

O3 Security · Impact-Aware SCA

Is CVE-2021-23420 in your dependencies?

Find it across Packagist, including transitive dependencies.

Scan my dependencies How O3 SCA works

CVSS Score

9.8/10CVSS v3 base

Vector breakdown

Attack Vector

Network

Attack Complexity

Low

Privileges Required

None

User Interaction

None

Scope

Unchanged

Confidentiality

High

Integrity

High

Availability

High

Raw vector

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CWE Classification

CWE-502Deserialization of Untrusted Data

Weaponization

No known public exploit tooling found.

OpenSSF Scorecard

Package health score

Codeception

4.9/10

Maintained6/10

Code-Review8/10

Branch-ProtectionN/A

Assessed Oct 5, 2026

Timeline

Disclosed

Aug 11, 2021

First exploit

Aug 19, 2021

Last updated

Jul 9, 2026

Identifiers

CVE-2021-23420

GHSA-4574-qv3w-fcmg

References

Advisorysnyk.io Advisorynvd.nist.gov Advisorygithub.com Fixgithub.com Webgithub.com Webgithub.com Webgithub.com Webgithub.com Webgithub.com Webgithub.com Packagegithub.com Evidencegithub.com

Related vulnerabilities

This CVE is critical severity; 4 of 8 other CVEs with CWE-502 are rated as high or higher (top: critical).

CVE-2025-66455CVE-2025-59953CVE-2026-49400CVE-2026-50646CVE-2026-78683CVE-2026-79657GHSA-gqvg-gmmx-x4hmCVE-2026-55175Browse all CWE-502

Provenance

Sources

OSV.devNVDFIRST.org (EPSS)

Last verifiedJul 9, 2026

CVE-2021-23420 — codeception

EPSS Exploitation Probability

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

Description

Affected Packages

Affected Products

Detection & mitigation playbook

Detect

Fix

Workarounds

Frequently Asked Questions

Is CVE-2021-23420 in your dependencies?