Description
Composer is a dependency Manager for the PHP language. Prior to 1.10.28, 2.2.28, and 2.9.8, Composer\IO\BaseIO::loadConfiguration() validates GitHub OAuth tokens with the regex ^[.A-Za-z0-9_]+$ and interpolates rejected tokens into an UnexpectedValueException; GitHub Actions GITHUB_TOKEN values using the ghs_<id>_<base64url-JWT> format can contain -, fail validation, and be disclosed to stderr or CI logs. This issue is fixed in versions 1.10.28, 2.2.28, and 2.9.8.
References9
- github.com/composer/composer/commit/3f5e7f9fbfa541137d6d1d5643e…
- github.com/composer/composer/commit/65e6390c49f1a11cd8b660d8182…
- github.com/composer/composer/commit/e66c8fdb7ff5409bd2f358c5f19…
- github.com/composer/composer/pull/12853
- github.com/composer/composer/pull/12855
- github.com/composer/composer/releases/tag/1.10.28
- github.com/composer/composer/releases/tag/2.2.28
- github.com/composer/composer/releases/tag/2.9.8
- github.com/composer/composer/security/advisories/GHSA-f9f8-rm49…
Metrics
- CVSS 3.1
-
7.5
HIGH
Score source: CNA
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N - EPSS — exploit probability
- 1% percentile: 64 · as of 15 November 2026
- CWE
- CWE-200
Could this be exploited in your environment?
A patch closes the known hole. A penetration test shows what an attacker can still reach — with proof.