CVE-2026-40575: critical vulnerability in oauth2-proxy
OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing
Published · Updated
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28Vexday Risk Score
No sign of exploitation. No public exploitation artifact known so far.
ssvc Trackcvss 9.1epss 0.5%
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.
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N
Affected products
oauth2-proxy · oauth2-proxyRelated CVEs — oauth2-proxy
In the same product, most dangerous first.
CVE-2021-21291MEDIUMSubdomain checking of whitelisted domains could allow unintended redirectsEPSS 1.6%CVE-2025-54576CRITICALOAuth2-Proxy has authentication bypass in oauth2-proxy skip_auth_routes due to Query Parameter inclusionEPSS 1.2%CVE-2021-21411MEDIUMIncorrect authorization in OAuth2-ProxyEPSS 1.1%CVE-2025-64484HIGHOAuth2-Proxy vulnerable to header smuggling via underscore, leading to potential privilege escalationEPSS 0.7%CVE-2026-34457CRITICALOAuth2 Proxy: Health Check User-Agent Matching Bypasses Authentication in auth_request ModeEPSS 0.5%CVE-2026-76835CRITICALOAuth2 Proxy 7.15.2 through 7.15.4 Authentication Bypass via X-Forwarded-Uri Under the Default Trusted Proxy SetEPSS 0.5%