How severe is CVE-2026-84361?

No CVSS score has been assigned to CVE-2026-84361 yet. Review the advisory details and affected package list to assess your exposure.

Which packages are affected by CVE-2026-84361?

CVE-2026-84361 affects the following packages: composer/composer (Packagist), composer/composer (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2026-84361?

Update composer/composer to 2.10.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-84361 is resolved across your whole dependency graph.

How do I detect CVE-2026-84361 in my Packagist dependencies?

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

How do I mitigate CVE-2026-84361 if there is no patch (or I can't update yet)?

Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Is CVE-2026-84361 actively exploited in the wild?

No public exploit code has been indexed for CVE-2026-84361 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-2026-84361?

CVE-2026-84361 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-2026-84361?

CVE-2026-84361 is classified as OS Command Injection (CWE-78). 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-2026-84361 published, and has it been updated?

CVE-2026-84361 was published on September 1, 2026 and was last updated on September 29, 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-2026-84361 — composer

Fix: composer/composer@0aac505

CVE-2026-84361 is a OS Command Injection vulnerability in composer/composer. A fix is available for composer/composer — see the affected versions and patch details below.

Composer: Perforce source URL permits P4PORT `rsh:` command execution

Also known asBIT-composer-2026-84361GHSA-rvx4-ffvw-m9q3

Published

Sep 1, 2026

Updated

Sep 29, 2026

Affected

2 pkgs

Patched

2 / 2

Exploits

None indexed

Exploitation data as of Oct 15, 2026 · OSV.dev, NVD, FIRST.org (EPSS)

Exploitation Status

No confirmed exploitation observed yet

A successful exploit gives an attacker total control of the affected component, not partial access.
CISA’s own triage has not observed active exploitation or public proof-of-concept code for this CVE as of its last assessment.

Exploitation and automatability from CISA’s SSVC triage for CVE-2026-84361.

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

2 pkgs affected

🐘composer/composer🐘composer/composer

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

If the p4 Perforce CLI client is installed, a malicious dependency package from a package repository allowing arbitrary perforce source URLs (packagist.org is safe) could execute arbitrary commands when running composer install or composer update. Composer passed a package's Perforce source address to the p4 CLI client without validating it. The p4 CLI client accepts addresses that mean "run this local command" instead of "connect to this server". This is remote code execution with the privileges of the user or CI account running Composer.

Am I affected?

You are only affected if all of the following are true:

The Perforce p4 command line client is installed and on the PATH of the machine running Composer.
An attacker can control a package metadata's source section with a perforce type. Packagist.org does not allow perforce source metadata, so you are only exploitable if you rely on another Composer repository (any custom composer-type repository, or an inline package repository entry), or a composer.lock file you obtained from somewhere you do not trust.
The package gets installed from source, either because it has no dist artifact or because source installs are selected (for example --prefer-source).

Plainly not affected: anyone without the p4 client installed, which is the large majority of Composer users. Perforce is an optional VCS integration. Also not affected: projects that only consume packages from Packagist.org, which does not allow Perforce source repositories and therefore cannot serve a package with a Perforce source address.

Most realistic way to get hit: a developer workstation or CI image that has Perforce tooling installed, pulling packages from a private or third party Composer repository that an attacker has compromised.

Patched versions

Composer now validates Perforce source addresses before handing them to the p4 client, and accepts only real network endpoints (an optional tcp/ssl transport with a host and port). Addresses that make the client spawn a local process are rejected, and the package fails validation on both update and install, before any p4 command runs. Fixed in Composer 2.10.3 and 2.2.30.

Note: If you legitimately use Perforce with an unusual P4PORT value that is not a plain host and port, Composer will now reject it.

Workarounds

Upgrading is the only complete fix.

Risk reduction short of upgrading:

Remove the p4 client from the PATH of machines that run Composer but do not use Perforce. This fully blocks this specific attack, since the vulnerability depends on that client being present.
Restrict configured repositories to sources you control or trust, and treat lock files from untrusted sources as untrusted input.

Affected Packages

2 total 2 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`composer/composer`	≥ 2.3.0&&< 2.10.3	2.10.3`composer require composer/composer:^2.10.3`
🐘Packagist	`composer/composer`	≥ 1.0&&< 2.2.30	2.2.30`composer require composer/composer:^2.2.30`

Detection & mitigation playbook

Open-source dependency

Detect
Scan your dependency tree (package-lock.json, pnpm-lock.yaml, requirements.txt, go.sum, etc.) for composer/composer, including transitive dependencies — a direct dependency you never call can still pull in a vulnerable version.
Fix
Update composer/composer to 2.10.3 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2026-84361 is resolved across your whole dependency graph.
Workarounds
Stop passing untrusted input into the interpreter or shell: call the affected binary with an argument array rather than a composed command string, reject anything outside a strict allowlist of expected values, and run the component under an account that cannot reach beyond the work it legitimately does.

Fixing This On Your OS

If you run this on a Linux distribution, patch through your package manager against the distro's own security advisory below — it tracks the exact backported fix for your release, which can ship on a different timeline (and sometimes a different severity) than the upstream project.

Red HatImportant

Workaround published by Red Hat

To mitigate this issue, avoid installing the Perforce `p4` client on systems where Composer is used, unless explicitly required. Additionally, ensure that Composer only processes dependencies from trusted repositories and `composer.lock` files to prevent the introduction of malicious `source.url` values.

Source: Red Hat security advisory for CVE-2026-84361 (CC BY 4.0)

Product	Fixed in	Advisory
Red Hat Hardened Images	`composer-main-2.10.3-1.hum1`	RHSA-2026:63151

Frequently Asked Questions

## Summary If the `p4` Perforce CLI client is installed, a malicious dependency package from a package repository allowing arbitrary perforce source URLs (packagist.org is safe) could execute arbitrary commands when running `composer install` or `composer update`. Composer passed a package's Perforce source address to the `p4` CLI client without validating it. The `p4` CLI client accepts addresses that mean "run this local command" instead of "connect to this server". This is remote code execution with the privileges of the user or CI account running Composer. ## Am I affected? You are only

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