GHSA-pxq7-h93f-9jrg OAuth2 Proxy has an Authentication Bypass via Fragment Confusion in skip_auth_routes and skip_auth_regex

• Go github.com/oauth2-proxy/oauth2-proxy/v7: >= 7.5.0, < 7.15.2 → fixed in 7.15.2

Impact A configuration-dependent authentication bypass exists in OAuth2 Proxy. Deployments are affected when all of the following are true: • Use of `skip_auth_routes` or the legacy `skip_auth_regex` * Use of patterns that can be widened by attacker-controlled suffixes, such as `^/foo/.*/bar$` causing potential exposure of `/foo/secret` * Protected upstream applications that interpret `#` as a fragment delimiter or otherwise route the request to the protected base path In deployments that rely on these settings, an unauthenticated attacker can send a crafted request containing a number sign in the path, including the browser-safe encoded form `%23`, so that OAuth2 Proxy matches a public allowlist rule while the backend serves a protected resource. Deployments that do not use these skip-auth options, or that only allow exact public paths with tightly scoped method and path rules, ARE NOT affected. Patches A fix has been implemented to normalize request paths more conservatively before skip-auth matching so fragment content does not influence allowlist decisions. Released as part of `v7.15.2` Workarounds Users who cannot upgrade immediately can reduce exposure by tightening or removing `skip_auth_routes` and `skip_auth_regex` rules, especially patterns that use broad wildcards across path segments. Recommended mitigations: • Replace broad rules with exact, anchored public paths and explicit HTTP methods • Reject requests whose path contains `%23` or `#` at the ingress, load balancer, or WAF level • Avoid placing sensitive application paths behind broad `skip_auth_routes` rules