Summary
Composer: Arbitrary file write outside vendor via malicious transitive package name
A maliciously crafted package, published on an untrusted third party repository other than Packagist.org or Private Packagist, can cause Composer to write files outside the vendor/ directory and outside your project, with attacker-controlled content, during a normal install or update through using an invalid package name, which was not correctly validated by Composer.
This is an arbitrary file write that can be used to execute code outside the Composer project's context in which you expected the package code to execute (for example by writing shell startup files, SSH authorized_keys, or a cron entry). It is a supply-chain issue: it requires a malicious or compromised package to be present in the dependency graph, it is not otherwise remotely exploitable against a machine.
The fix makes Composer validate every package produced by dependency resolution before anything is written to composer.lock or installed, and abort with a security error if a package name is not a valid vendor/package name.
Am I affected?
You may be affected if you install packages from an untrusted third party repository, which does not sufficiently validate package names. Packagist.org and Private Packagist are safe, as they validate package names correctly.
Patched versions
Fixed in 2.2.29 and 2.10.2. Composer 1.x is also affected and you should move to a safe 2.x release.
Workarounds
Do not use untrusted package repositories. If you have to, mirror them through an internal repository like Private Packagist.
Impact
Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files. Typical impact: unauthorized file read or write outside the intended directory.
CVE-2026-59948 has a CVSS score of 7.0 (High). The vector is requires local access, no privileges required, and user interaction required. A CVSS score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether this affects your application depends on whether the vulnerable code is present and reachable in your environment. A fixed version is available (2.10.2, 2.2.29); upgrading removes the vulnerable code path.
Affected versions
Security releases
Kodem intelligence
Severity tells you how bad this could be in the worst case. It does not tell you whether you are exposed. Exploitability and impact are functions of runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A vulnerable package can sit in your dependency tree and never run.
Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter. Kodem's runtime-powered SCA identifies whether this CVE is reachable in your applications.
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composer/composer to 2.10.2 or later; composer/composer to 2.2.29 or later
Kodem Kai can prioritize this vulnerability in your dependency tree and generate a fix recommendation.
Frequently Asked Questions
- What is CVE-2026-59948? CVE-2026-59948 is a high-severity path traversal vulnerability in composer/composer (composer), affecting versions >= 2.3.0, < 2.10.2. It is fixed in 2.10.2, 2.2.29. Input manipulates file paths to reach files outside the intended directory, such as configuration or credential files.
- How severe is CVE-2026-59948? CVE-2026-59948 has a CVSS score of 7.0 (High). This score reflects the worst-case severity of the vulnerability, not your specific exposure. Whether it represents real risk in your environment depends on whether the vulnerable code is present and reachable.
- Which versions of composer/composer are affected by CVE-2026-59948? composer/composer (composer) versions >= 2.3.0, < 2.10.2 is affected.
- Is there a fix for CVE-2026-59948? Yes. CVE-2026-59948 is fixed in 2.10.2, 2.2.29. Upgrade to this version or later.
- Is CVE-2026-59948 exploitable, and should I be worried? Whether CVE-2026-59948 is exploitable in your environment depends on whether the vulnerable code is present and reachable. A CVSS score is a worst-case rating; it does not account for your specific deployment, configuration, or usage patterns. Kodem, an Intelligent Application Security platform, uses runtime intelligence to show which vulnerabilities actually execute in production, so you can focus on the ones that represent real risk. Get a demo
- What actually determines whether CVE-2026-59948 is exploitable, and how bad it is? Exploitability and impact are not fixed properties of a CVE. They depend on runtime truth: whether the vulnerable code is present, reachable, and actually executes in your application. A high CVSS score on a dependency that never runs is not the same as real risk. Kodem, an Intelligent Application Security platform, uses runtime intelligence to reveal which vulnerabilities actually execute in production, so teams prioritize the ones that genuinely matter.
- How do I fix CVE-2026-59948?
- Upgrade
composer/composerto 2.10.2 or later - Upgrade
composer/composerto 2.2.29 or later
- Upgrade