CVE-2015-8371 in Composer
Summary
by MITRE • 09/21/2023
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.
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Analysis
by VulDB Data Team • 08/25/2025
The vulnerability CVE-2015-8371 represents a critical cache poisoning flaw in the Composer dependency management system for php applications. This vulnerability exists in Composer versions prior to 2016-02-10 and specifically affects the way dist packages are cached during the build process. The flaw stems from insufficient cache key derivation mechanisms that fail to adequately protect against malicious interference from other projects hosted on the same system. When multiple projects share the same caching infrastructure, an attacker can manipulate the cache by creating malicious packages that exploit the predictable cache key generation process. This vulnerability directly maps to CWE-200, which addresses information exposure, and CWE-444, which covers insufficient input validation.
The technical implementation of this vulnerability occurs when Composer generates cache keys for dist packages using predictable elements such as package names, dist types, and repository metadata including commit hashes. Since commit hashes can be easily discovered or guessed by attackers, they become part of the cache key generation process, creating opportunities for cache poisoning attacks. The cache key construction process fails to incorporate sufficient entropy or cryptographic protection to ensure that different packages cannot collide or interfere with each other's cached representations. This allows an attacker to craft malicious package distributions that will be cached under legitimate package names, effectively enabling code injection into the build process of other projects. The vulnerability operates at the intersection of software supply chain security and cache management protocols, creating a path for persistent malicious code delivery.
The operational impact of this vulnerability extends beyond simple code injection to encompass complete compromise of server-side build processes and potential system-wide infiltration. When an attacker successfully poisons the cache, any project that depends on the affected package will execute the attacker-controlled code during its build process, potentially leading to remote code execution, data exfiltration, or further system compromise. The vulnerability is particularly dangerous in shared hosting environments or containerized deployments where multiple projects may share the same Composer cache directory. This creates a scenario where a single malicious actor can compromise numerous projects simultaneously, making the attack vector highly scalable. The attack follows typical supply chain compromise patterns described in the MITRE ATT&CK framework under the T1195.002 technique for supply chain compromise, where attackers target dependency management systems to gain access to multiple downstream systems.
Mitigation strategies for CVE-2015-8371 require immediate version upgrades to Composer 1.0.0 or later, which implements proper cache key generation mechanisms that prevent cross-project interference. Organizations should also implement cache isolation measures, ensuring that different projects maintain separate cache directories or employ cryptographic protections for cache keys. Additional defensive measures include implementing proper package verification procedures, using trusted package sources exclusively, and monitoring for unauthorized package modifications. The vulnerability highlights the importance of secure cache design principles and demonstrates how seemingly minor implementation flaws in dependency management systems can create significant security risks. Security teams should conduct comprehensive audits of their dependency management systems and ensure that all projects are updated to versions that address this specific cache poisoning vulnerability. The fix implemented in Composer 1.0.0 specifically addresses the root cause by strengthening cache key derivation to include cryptographic hashing of repository metadata, preventing attackers from predicting or manipulating cache entries.