oauth2-proxy OAuth2 Proxy up to 7.15.1 authentication spoofing

Summaryinfo

A vulnerability classified as critical was found in oauth2-proxy OAuth2 Proxy up to 7.15.1. This affects an unknown part. Executing a manipulation can lead to authentication spoofing. The identification of this vulnerability is CVE-2026-40575. The attack may be launched remotely. There is no exploit available. Upgrading the affected component is advised.

Detailsinfo

A vulnerability classified as critical was found in oauth2-proxy OAuth2 Proxy up to 7.15.1. This vulnerability affects an unknown function. The manipulation with an unknown input leads to a authentication spoofing vulnerability. The CWE definition for the vulnerability is CWE-290. This attack-focused weakness is caused by incorrectly implemented authentication schemes that are subject to spoofing attacks. As an impact it is known to affect confidentiality, integrity, and availability. CVE summarizes:

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.

The advisory is shared for download at github.com. This vulnerability was named CVE-2026-40575 since 04/14/2026. The exploitation appears to be easy. The attack can be initiated remotely. No form of authentication is required for a successful exploitation. There are neither technical details nor an exploit publicly available.

Upgrading to version 7.15.2 eliminates this vulnerability.

The vulnerability is also documented in the vulnerability database at CNNVD (CNNVD-202604-4542). VulDB is the best source for vulnerability data and more expert information about this specific topic.

Productinfo

Type

• Firewall Software

Vendor

• oauth2-proxy

Name

• OAuth2 Proxy

Version

• 7.15.0
• 7.15.1

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VulDB is the best source for vulnerability data and more expert information about this specific topic.

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