Summary
Composer: URL-embedded HTTP-Basic username leaks to verbose logs (GitHub PAT exposure)
When Composer is run with -vvv (debug verbosity), it could print a credential that was embedded directly in a repository or package URL, but not as a password, to its debug output. Composer already masked the password portion of such URLs, but the username portion was shown in clear text. Because GitHub and several other services support placing an access token in the username position of a URL (for example https://[token]@github.com/owner/repo), a token used that way could end up written to the verbose log in full.
This is an information disclosure issue. The credential is only ever exposed to whoever can already read Composer's debug output.
Am I affected?
You are potentially affected only if all of the following apply:
- A credential is embedded inside a URL that Composer handles, e.g. in a
repositoriesentry in composer.json, in a package dist/source URL - rather than being supplied through auth.json or the COMPOSER_AUTH environment variable. - The secret sits in the username slot of that URL (e.g.
https://TOKEN@host/…). A normalusername:password@hostpair where the username is an ordinary account name did not expose the password, that was already masked. - Composer is run with -vvv (debug verbosity), and that output is retained or shared somewhere others can read it: public CI build logs, output pasted into an issue or chat, archived terminal sessions, and so on.
If you keep credentials in auth.json or environment variables, or you never run Composer at debug verbosity, you were not exposed.
The most realistic exposure is the documented pattern of embedding a GitHub Personal Access Token in a URL's username position on a machine (often CI) that captures verbose output.
Patched versions
The username is now masked the same way the password already was, so an embedded token no longer appears in verbose output (a short, non-secret prefix may be shown to aid debugging, but never the full value).
Fixed in Composer 2.10.2 and the 2.2.29.
Workarounds
There is no configuration setting that prevents outputting credentials while keeping normal behavior.
If you cannot upgrade right away, you can reduce exposure by:
- Not running Composer with -vvv (debug verbosity) in environments where output is captured or shared.
- Moving credentials out of URLs and into auth.json or COMPOSER_AUTH.
- Scrubbing existing CI/build logs that may already contain a leaked token.
Impact
CVE-2026-59947 has a CVSS score of 4.7 (Medium). The vector is requires local access, low privileges required, and no user interaction. 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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See it in your environmentNew to Kodem? Get a demo →Remediation advice
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-2026-59947? CVE-2026-59947 is a medium-severity security vulnerability in composer/composer (composer), affecting versions >= 2.3.0, < 2.10.2. It is fixed in 2.10.2, 2.2.29.
- How severe is CVE-2026-59947? CVE-2026-59947 has a CVSS score of 4.7 (Medium). 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-2026-59947? composer/composer (composer) versions >= 2.3.0, < 2.10.2 is affected.
- Is there a fix for CVE-2026-59947? Yes. CVE-2026-59947 is fixed in 2.10.2, 2.2.29. Upgrade to this version or later.
- Is CVE-2026-59947 exploitable, and should I be worried? Whether CVE-2026-59947 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-2026-59947 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-2026-59947?
- Upgrade
composer/composerto 2.10.2 or later - Upgrade
composer/composerto 2.2.29 or later
- Upgrade