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CVE-2026-45793 high CVSS 7.5

Information Disclosure in composer/composer (CVE-2026-45793)

Summary

Vulnerability in composer/composer (CVE-2026-45793). Confidential information can be exposed externally. Exploitable via GITHUB_TOKEN. Mitigation: upgrade to 1.10.28 or later.

Original description

The description as published by the source.

Summary

Composer leaks the full contents of tokens configured as GitHub OAuth tokens if they do not match Composer's expected format for such tokens to stderr. GitHub has introduced a new format for GitHub Actions GITHUB_TOKEN values. These tokens are validated in the same way by Composer on GitHub Actions. The new format including a - (hyphen) fails Composer's validation and leads to disclosure of the GITHUB_TOKEN in logs.

Many widely-used Actions (e.g. shivammathur/setup-php) auto-register GITHUB_TOKEN into composer's global auth.json, so the leak triggers without any unusual user configuration.

GitHub Actions tokens expire when the associated job finishes, and they are scoped to the respective repository only. So in most regular cases the Composer validation, which errors while leaking the token, also immediately ends the job, expiring the token immediately. Tokens expire at the very latest after 6 hours on GitHub-hosted runners. If you use self-hosted runner, expiration is at most 24 hours after creation. The new token format is being rolled out gradually, so not all repositories are affected yet, but will be soon.

Classic ghp_ PATs are not affected by the regex bug per se, but the same leak primitive applies to any future credential that fails validation for any reason.

Details

When a GitHub token fails regular expression validation of the character set, the rejected token is interpolated verbatim into the UnexpectedValueException message thrown…

Source: GitHub Security Advisories (Global) NVD GitHub Advisory

Auto-generated summary

Assembled by SecPulse from the source data (CVSS, CWE, affected versions) using templates — no AI involved. Check the original description and references below for exact details.

A vulnerability tracked as CVE-2026-45793 has been found in composer/composer.
Attackers can target a specific entry point like GITHUB_TOKEN over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 7.5/10.
What to do: upgrade composer/composer to 1.10.28 or later.
If unsure, ask your IT team or search "composer/composer CVE-2026-45793" on the vendor's site.

CVE-2026-45793 (composer/composer) — CWE-200 / CVSS v3 7.5
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: GITHUB_TOKEN / ghp_ / UnexpectedValueException / main
Patched: 1.10.28 — apply immediately
Plan: 1) Audit SBOM/dependencies, 2) Stage→prod upgrade, 3) Add WAF/proxy monitoring on affected endpoints, 4) Hunt IOCs in logs.
Refs: see the GHSA / vendor advisory / patched release linked on this page.

❓ What is the problem

Information disclosure (CWE-200) exists in composer/composer. Attackers reach the vulnerable code path via GITHUB_TOKEN without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of composer/composer. Attack surface: GITHUB_TOKEN / ghp_ / UnexpectedValueException / main.

🔥 Severity

Severity: High (CVSS 7.5/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 1.10.28.

🛡️ Workaround

Until the patch is applied: disable the affected feature, apply WAF rules, or restrict access via network ACLs.

🔍 Detection

Search webserver/proxy logs for unusual request patterns matching this CVE's known IOCs. Run grep -r 'composer/composer' . against your dependency files (package-lock.json, requirements.txt, go.sum) to find affected services.

Response actions

Concrete steps and command examples for SOC/SRE teams to execute in order

  1. 1
    Identify exposure identify 
    grep -r 'composer/composer' . | grep -v node_modules

    リポジトリと本番環境の依存ファイル (package-lock.json / requirements.txt / go.sum / Gemfile.lock 等) で composer/composer を grep し、稼働しているサービス・バージョンを把握する。

  2. 2
    Apply patch patch 
    Upgrade composer/composer to 1.10.28

    ステージング環境で 1.10.28 に上げて回帰テスト → 本番反映。回帰テストはアプリの主要ハッピーパスを含めること。

  3. 3
    Post-deployment verification verify 
    Confirm patched version is live in production

    パッチ適用後、ステージングで PoC または同等の悪用パターンを再現して脆弱性が閉じたことを確認。本番ではアクセスログ・WAF でアラート再発が無いか継続監視。

Affected packages

composer composer/composer
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"1.10.28"}]}]
Packagist composer/composer
[{"type":"ECOSYSTEM","events":[{"introduced":"1.0"},{"fixed":"1.10.28"}]}]
Bitnami composer
[{"type":"SEMVER","events":[{"introduced":"1.0.0"},{"fixed":"1.10.28"},{"introduced":"2.0.0"},{"fixed":"2.2.28"},{"introduced":"2.3.0"},{"fixed":"2.9.8"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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