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CVE-2026-40575 critical CVSS 9.1

Vulnerability in github.com/oauth2-proxy/oauth2-proxy/v7 (CVE-2026-40575)

Summary

Vulnerability in github.com/oauth2-proxy/oauth2-proxy/v7 (CVE-2026-40575). Confidential information can be exposed externally. Mitigation: upgrade to 7.15.2 or later.

Original description

The description as published by the source.

Impact

A configuration-dependent authentication bypass exists in OAuth2 Proxy.

Deployments are affected when all of the following are true:

  • OAuth2 Proxy is configured with --reverse-proxy
  • and at least one rule is defined with --skip_auth_routes or the legacy --skip-auth-regex

OAuth2 Proxy may trust a client-supplied X-Forwarded-Uri header when --reverse-proxy is enabled and --skip-auth-route or --skip-auth-regex is configured. An attacker can spoof this header so OAuth2 Proxy evaluates authentication and skip-auth rules against a different path than the one actually sent to the upstream application.

This can result in an unauthenticated remote attacker bypassing authentication and accessing protected routes without a valid session.

Patches

This issue is addressed as part of the newly introduced --trusted-proxy-ip flag in v7.15.2. If you leave it unset, OAuth2 Proxy will continue to trust ALL source IPs (0.0.0.0/0) for backwards compatibility, which means a client may still be able to spoof forwarded headers. Therefore after upgrading we urge you to use the new --trusted-proxy-ip flag to set the IPs or CIDR ranges of the reverse proxies that are allowed to send X-Forwarded-* headers and furthermore implement the mitigation steps outlined below to properly configure your load balancer infrastructure.

Mitigation

  • Strip any client-provided X-Forwarded-Uri header at the reverse proxy or load balancer level
  • Explicitly overwrite…

Source: NIST National Vulnerability Database 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-2026-40575 has been found in github.com/oauth2-proxy/oauth2-proxy/v7.
Confidential information can be exposed externally. CVSS score: 9.1/10.
What to do: upgrade github.com/oauth2-proxy/oauth2-proxy/v7 to 7.15.2 or later.
If unsure, ask your IT team or search "github.com/oauth2-proxy/oauth2-proxy/v7 CVE-2026-40575" on the vendor's site.

CVE-2026-40575 (github.com/oauth2-proxy/oauth2-proxy/v7) — CWE-290 / CVSS v3 9.1
Attack vector: remote (network-reachable) / unauthenticated / no user interaction
Patched: 7.15.2 — 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

A vulnerability (CWE-290) exists in github.com/oauth2-proxy/oauth2-proxy/v7.

📍 Affected scope

Check the vendor advisory for the affected versions of github.com/oauth2-proxy/oauth2-proxy/v7.

🔥 Severity

Severity: Critical (CVSS 9.1/10). Confidential information can be exposed externally.

🔧 How to fix

Update to 7.15.2.

🛡️ 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 'github.com/oauth2-proxy/oauth2-proxy/v7' . 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 'github.com/oauth2-proxy/oauth2-proxy/v7' . | 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 github.com/oauth2-proxy/oauth2-proxy/v7 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 github.com/oauth2-proxy/oauth2-proxy/v7 to 7.15.2

    ステージング環境で 7.15.2 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

go github.com/oauth2-proxy/oauth2-proxy/v7
[{"type":"ECOSYSTEM","events":[{"introduced":"0"},{"fixed":"7.15.2"}]}]

References

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