How severe is CVE-2023-43655?

CVE-2023-43655 has a CVSS score of 6.4/10, rated MEDIUM. Review your exposure and patch according to your risk tolerance.

Which packages are affected by CVE-2023-43655?

CVE-2023-43655 affects the following packages: composer/composer (Packagist), composer/composer (Packagist), composer/composer (Packagist). Ecosystems affected: Packagist.

How do I fix CVE-2023-43655?

Update composer/composer to 1.10.27 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-43655 is resolved across your whole dependency graph.

How do I detect CVE-2023-43655 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-2023-43655 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.

Is CVE-2023-43655 actively exploited in the wild?

No public exploit code has been indexed for CVE-2023-43655 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-2023-43655?

CVE-2023-43655 has an EPSS (Exploit Prediction Scoring System) score of 1.5%, placing it in the 75th 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-2023-43655?

CVE-2023-43655 is classified as CWE-74 (CWE-74). This weakness type describe the underlying flaw category, which helps determine the potential impact and the right class of mitigation.

When was CVE-2023-43655 published, and has it been updated?

CVE-2023-43655 was published on September 29, 2023 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

MEDIUM severity

CVE-2023-43655 — composer

MEDIUMFix: composer/composer@4fce147

CVE-2023-43655 is a medium-severity (CVSS 6.4) CWE-74 vulnerability in composer/composer. A fix is available for composer/composer — see the affected versions and patch details below.

Remote Code Execution via web-accessible composer.phar

Also known asBIT-composer-2023-43655GHSA-jm6m-4632-36hf

Published

Sep 29, 2023

Updated

Oct 28, 2026

Affected

3 pkgs

Patched

3 / 3

Exploits

None indexed

Exploitation data as of Nov 8, 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-2023-43655.

EPSS Exploitation Probability

via FIRST.org ↗

1.5%probability of exploitation in next 30 days

Lower Risk0.00%

Lower risk than most CVEs75th percentile — riskier than 75% of all scored CVEsHighest risk

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

How urgent is this, really

Where this sits among everything scored

Real-World Exposure

3 pkgs affected

🐘composer/composer🐘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

Composer is a dependency manager for PHP. Users publishing a composer.phar to a public web-accessible server where the composer.phar can be executed as a php file may be subject to a remote code execution vulnerability if PHP also has register_argc_argv enabled in php.ini. Versions 2.6.4, 2.2.22 and 1.10.27 patch this vulnerability. Users are advised to upgrade. Users unable to upgrade should make sure register_argc_argv is disabled in php.ini, and avoid publishing composer.phar to the web as this is not best practice.

Affected Packages

3 total 3 fixed

Ecosystem	Package	Vulnerable range	Fix
🐘Packagist	`composer/composer`	all versions	1.10.27`composer require composer/composer:^1.10.27`
🐘Packagist	`composer/composer`	≥ 2.0.0&&< 2.2.22	2.2.22`composer require composer/composer:^2.2.22`
🐘Packagist	`composer/composer`	≥ 2.3.0&&< 2.6.4	2.6.4`composer require composer/composer:^2.6.4`

Affected Products

3 products · 6 configurations

debian linuxdebian

1 version

10.0

fedorafedoraproject

2 versions

3738

Application

composergetcomposer

≥ 2.3.0 && < 2.6.4

range

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 1.10.27 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2023-43655 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.

Frequently Asked Questions

Composer is a dependency manager for PHP. Users publishing a composer.phar to a public web-accessible server where the composer.phar can be executed as a php file may be subject to a remote code execution vulnerability if PHP also has `register_argc_argv` enabled in php.ini. Versions 2.6.4, 2.2.22 and 1.10.27 patch this vulnerability. Users are advised to upgrade. Users unable to upgrade should make sure `register_argc_argv` is disabled in php.ini, and avoid publishing composer.phar to the web as this is not best practice.

O3 Security · Impact-Aware SCA

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