CVE-2026-34457: OAuth2 Proxy: Health Check User-Agent Matching Bypasses Authentication in auth_request Mode

Severity: critical (CVSS 9.1 v3.1)
Exploited in the wild: not listed in CISA KEV
EPSS: 0.5% probability of exploitation in the next 30 days
Public exploit or detection template: none known
Published: 2026-04-14 · updated 2026-07-24
Weakness: CWE-290

Description

OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Versions prior to 7.15.2 contain a configuration-dependent authentication bypass in deployments where OAuth2 Proxy is used with an auth_request-style integration (such as nginx auth_request) and either --ping-user-agent is set or --gcp-healthchecks is enabled. In affected configurations, OAuth2 Proxy treats any request with the configured health check User-Agent value as a successful health check regardless of the requested path, allowing an unauthenticated remote attacker to bypass authentication and access protected upstream resources. Deployments that do not use auth_request-style subrequests or that do not enable --ping-user-agent/--gcp-healthchecks are not affected. This issue is fixed in 7.15.2.

Affected products

oauth2-proxy: before 7.15.2 — fixed in 7.15.2

How to fix

Upgrade to a fixed version: oauth2-proxy 7.15.2. Check the vendor advisory for mitigations.

References

Get alerted when CVE-2026-34457 or the next vulnerability affects your stack