CVE-2026-40575 OAuth2 Proxy has an Authentication Bypass via X-Forwarded-Uri Header Spoofing
Attackers can bypass authentication and access protected routes by spoofing the X-Forwarded-Uri header in specific reverse proxy configurations.
- Exploited in the wild
- Not known
- Login needed
- Not needed
- Attackable
- Over the internet
- Victim action needed
- Not needed
- Fix
- Available
What is CVE-2026-40575?
CVE-2026-40575 is a critical authentication bypass vulnerability in oauth2-proxy, published on 21 Apr 2026. An attacker can exploit it over the internet without logging in, with no action from the victim.
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.
Weakness: CWE-290
Which versions are affected by CVE-2026-40575?
It affects 1 product.
Linux distribution packages (1)
oauth2-proxy Red Hat:hummingbird:1 | All versions | 0:7.15.4-0.1.hum1 |
Products include Oauth2 Proxy Project Oauth2 Proxy.
How do I fix CVE-2026-40575?
Upgrade to a fixed version.
Upgrade, and rotate credentials and sessions that may have been exposed. More about Authentication bypass.
Is CVE-2026-40575 being exploited?
There is no known exploitation of CVE-2026-40575 in the wild and no public exploit code.
Other vulnerabilities in oauth2-proxy
- CVE-2026-34457 OAuth2 Proxy: Health Check User-Agent Matching Bypasses Authentication in auth_request Mode
- CVE-2025-54576 OAuth2-Proxy has authentication bypass in oauth2-proxy skip_auth_routes due to Query Parameter inclusion
- CVE-2017-1000069 Cross-site Request Forgery (CSRF)
- CVE-2026-41059 OAuth2 Proxy has an Authentication Bypass via Fragment Confusion in skip_auth_routes and skip_auth_regex
- CVE-2020-11053 Open Redirect in OAuth2 Proxy
Sources
Also known as MINI-3f4m-gp5w-9f2p, MINI-mmxf-q5j4-jm29, RHSA-2026:58471.