CVE-2015-8371 — composer
HIGHCVE-2015-8371 is a high-severity (CVSS 8.8) CWE-345 vulnerability in composer/composer. 1 public exploit or proof-of-concept reference is indexed, so weaponization risk is real. A fix is available for composer/composer — see the affected versions and patch details below.
Composer allows cache poisoning from other projects built on the same host
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.
- A successful exploit gives an attacker total control of the affected component, not partial access.
Exploitation and automatability from CISA’s SSVC triage for CVE-2015-8371.
EPSS Exploitation Probability
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
composer/composerReal-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 before 2016-02-10 allows cache poisoning from other projects built on the same host. This results in attacker-controlled code entering a server-side build process. The issue occurs because of the way that dist packages are cached. The cache key is derived from the package name, the dist type, and certain other data from the package repository (which may simply be a commit hash, and thus can be found by an attacker). Versions through 1.0.0-alpha11 are affected, and 1.0.0 is unaffected.
Affected Packages
| Ecosystem | Package | Vulnerable range | Fix |
|---|---|---|---|
| 🐘Packagist | composer/composer | all versions | 1.0.0composer require composer/composer:^1.0.0 |
Affected Products
composergetcomposerResearch use only. For defensive security, authorized penetration testing, and academic research only. Never execute exploit code against systems without explicit written authorization.
Detection & mitigation playbook
Open-source dependencyDetect
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 1.0.0 or later, then make sure no transitive (indirect) dependency still pins the vulnerable range — O3 confirms CVE-2015-8371 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
Is CVE-2015-8371 in your dependencies?
Find it across Packagist, including transitive dependencies.