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Vulnerability · Published Apr 21, 2026 · Assigned by GitHub_M

CVE-2026-40575OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing

Critical 9.1

In plain English

A critical-severity authentication bypass by spoofing in oauth2-proxy from oauth2-proxy. There are no confirmed reports of exploitation so far. The chance it is exploited in the next 30 days is estimated at 0.5% (higher than 41% of all known vulnerabilities). Fixed versions are available - upgrade the affected package.

Severity (CVSS 3.1)9.1Critical
Exploit odds (30 days)0.5%top 58.6% of all CVEs
Exploited in the wildNo reportsCISA SSVC: none
Attack toolingNoneno public tooling known

Official description

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.

Affected packages & fixed versions

EcosystemPackageFixed inAdvisory
Gogithub.com/oauth2-proxy/oauth2-proxyno fix listedGO-2026-5236
Gogithub.com/oauth2-proxy/oauth2-proxy/v77.15.2GHSA-7x63-xv5r-3p2x
Gogithub.com/oauth2-proxy/oauth2-proxy/v77.15.2GO-2026-5236

Affected products (as reported)

VendorProductVersions
oauth2-proxy oauth2-proxy >= 7.5.0, < 7.15.2

Weakness: CWE-290 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

References