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CVE-2026-54603 high CVSS 8.6

Information Disclosure in oauth2 (CVE-2026-54603)

Summary

Vulnerability in oauth2 (CVE-2026-54603). Confidential information can be exposed externally. Exploitable via GET /leak. Mitigation: upgrade to 2.0.22 or later.

Original description

The description as published by the source.

Summary

When an application uses OAuth2::Client (typically via an OAuth2::AccessToken) and the configured authorization server returns a redirect whose Location header is a protocol-relative URI of the form //attacker.example/leak, OAuth2::Client#request resolves the redirect with response.response.env.url.merge(location). Per RFC 3986 §5.2, an input that starts with // is a network-path reference and replaces the authority of the base URL: URI("http://idp.trusted/userinfo").merge("//attacker.example/leak") returns http://attacker.example/leak. The recursive request(verb, full_location, req_opts) call then re-sends the request to the attacker host while preserving the Authorization: Bearer header that OAuth2::AccessToken#configure_authentication! installed on req_opts[:headers] for the original request.

The result is a one-shot cross-origin credential disclosure: any 30x response from the IdP that an attacker can influence (a compromised endpoint, a tenant-controlled IdP in a multi-tenant deployment, or an open-redirect handler that does not normalise the Location it emits) can extract the bearer access token of the calling user.

Affected

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-2026-54603 has been found in oauth2.
Attackers can target a specific entry point like GET /leak over the network to misuse the product.
Confidential information can be exposed externally. CVSS score: 8.6/10.
What to do: upgrade oauth2 to 2.0.22 or later.
If unsure, ask your IT team or search "oauth2 CVE-2026-54603" on the vendor's site.

CVE-2026-54603 (oauth2) — CWE-200 / CVSS v3 8.6
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Attack surface: GET /leak / GET /userinfo / GET ///127.0.0.1 / Location
Patched: 2.0.22 — 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 oauth2. Attackers reach the vulnerable code path via GET /leak without authentication.

📍 Affected scope

Check the vendor advisory for the affected versions of oauth2. Attack surface: GET /leak / GET /userinfo / GET ///127.0.0.1 / Location.

🔥 Severity

Severity: High (CVSS 8.6/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 2.0.22.

🛡️ 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 GET /leak requests with malformed payloads or SQL meta-characters. Run grep -r 'oauth2' . 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 'oauth2' . | 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 oauth2 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
    Hunt for indicators of compromise detect 
    grep 'GET /leak' /var/log/nginx/access.log | grep -E '(unusual_payload|sqli_pattern)'

    アクセスログで GET /leak への異常なリクエスト (不正な認証ヘッダ・SQLメタ文字)を過去 30〜90日分捜索。WAF/SIEM があれば該当パスのアラート発火履歴を確認。

  3. 3
    Apply patch patch 
    Upgrade oauth2 to 2.0.22

    ステージング環境で 2.0.22 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と、Step 2 で見つけた異常検知の続報チェックを含めること。

  4. 4
    Post-deployment verification verify 
    Replay attack against GET /leak on staging to confirm patch closes the vector

    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 Step 2 と同じログクエリでアラート再発が無いか継続監視。

Affected packages

rubygems oauth2
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"2.0.22"}]}]

Fix status by distribution

Fixed packages published by each distribution for this CVE

References

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