Composer: Malicious Package Name Can Write Files Outside Vendor

Published as "Composer: Arbitrary file write outside vendor via malicious transitive package name"

high Composer · Last reviewed Nov 4, 2026

CVE: CVE-2026-59948
GHSA: GHSA-499r-g7pc-vmp9
Packagist: PKSA-zcdk-qnhk-hq2g
Reported: Jul 20, 2026

Lets a malicious package from a third-party repository write files anywhere the Composer user can, which can lead to running code.

Affected and fixed versions

In composer/composer. Find the row for the version you run, and update to the release next to it.

If you run	Update to	Support
2.3.0 – 2.10.1	2.10.2	Supported

Show 1 older branch, no longer supported

1.0.0 – 2.2.28

2.2.29

Upgrade

Run the line for the branch you are on.

composer require composer/composer:^2.10.2

What this means

A malicious package can make Composer write files with content the attacker chooses anywhere Composer's user can write, outside vendor/ and outside your project. Written to the right place, such as a shell startup file, SSH authorized_keys or a cron entry, that can lead to running the attacker's code.

Composer didn't check that every package name was a valid vendor/package name before installing.

Who is affected

Projects that install packages from a third-party Composer repository that doesn't check package names itself. Look at the repositories section of your composer.json. The Composer advisory says Packagist.org and Private Packagist are safe because they validate names. It's a supply-chain risk: a malicious or compromised package has to be in your dependencies.

What to do

Update composer/composer to 2.10.2, or to 2.2.29 if you stay on 2.2. Composer 1.x is also affected, so move to one of those 2.x releases. The fix checks every resolved package name before anything is written to composer.lock or installed, and stops with a security error otherwise.

Until you can update, don't use untrusted package repositories. If you need one, Composer suggests mirroring it through an internal repository such as Private Packagist.

Reported by iliaal.

Check your app with an agent

Paste this into a coding agent that can read your project, such as Claude Code, Codex or Amp. It checks your composer.lock against the versions above and tells you what to update, without changing anything.

Check whether the PHP project you have access to is affected by this security advisory, and tell me what to update. Do a read-only check: don't edit files, don't run composer update or composer require, and don't try to reproduce the flaw.

Advisory: Composer: Malicious Package Name Can Write Files Outside Vendor (CVE-2026-59948, GHSA-499r-g7pc-vmp9)
Details: https://phpnews.net/security/composer/ghsa-499r-g7pc-vmp9

Affected versions, as Composer constraints:
- composer/composer: >=1.0.0,<2.2.29|>=2.3.0,<2.10.2

Fixed releases on branches that still get security fixes:
- 2.3.0 – 2.10.1: update to 2.10.2

1. Find every composer.lock in the project outside vendor/ (a monorepo can have one per app) and read the installed version of each package above. Packages installed as dependencies of other packages count too.
2. Compare each installed version with its constraint: "|" separates alternative ranges, and "," means both bounds apply.
3. For each affected install, read "What this means" at https://phpnews.net/security/composer/ghsa-499r-g7pc-vmp9 and check whether the project meets the conditions it describes (a feature in use, a config value, a driver). Say which conditions you could check and which you couldn't.
4. Report a table: lock file | package | installed version | affected (yes, no or unknown) | conditions met (yes, no or unknown) | update to | evidence. For each affected package, give the command that would fix it, without running it: composer update <package> --with-dependencies when it is only installed as a dependency of another package, or composer require with the fixed version when composer.json requires it directly. If the installed version is on a branch with no fixed release listed, say it needs a move to a newer branch.

Sources

← All Composer advisories