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CVE-2026-40575

Oauth2 Proxy Project Oauth2 Proxy authentication bypass

9.1 CRITICALEPSS 0.73%
  1. Published21 Apr 2026

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.

CVSS 3.1 breakdown

Attack vectorNetwork
Attack complexityLow
Privileges requiredNone
User interactionNone
ScopeUnchanged
ConfidentialityHigh
IntegrityHigh
AvailabilityNone
CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:N

Affected products

Oauth2 Proxy Project Oauth2 Proxy≥ 7.5.0 < 7.15.2

Remediation

Fixed in
Oauth2 Proxy Project Oauth2 Proxy≥ 7.15.2

References

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Frequently asked

Is CVE-2026-40575 being actively exploited?

CVE-2026-40575 is not in the CISA KEV catalog. Its EPSS exploit probability is 0.73%.

How severe is CVE-2026-40575?

CVE-2026-40575 has a CVSS 3.1 base score of 9.1, rated critical. EPSS estimates a 0.73% probability of exploitation.

Which products are affected by CVE-2026-40575?

Affected products include Oauth2 Proxy Project Oauth2 Proxy.

How do I fix CVE-2026-40575?

Upgrade affected software to a fixed version, for example Oauth2 Proxy Project Oauth2 Proxy 7.15.2 or later, then confirm no affected versions remain in your inventory.

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Data from the NVD, CISA KEV catalog and FIRST EPSS. CVSS 3.1 base score shown where available.