Executive brief
### 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
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
Affected products
- Go github.com/oauth2-proxy/oauth2-proxy
- Go github.com/oauth2-proxy/oauth2-proxy/v7