OAuth2 Proxy has an Authentication Bypass via Fragment Confusion in skip_auth_routes and skip_auth_regex

OAuth2 Proxy is a reverse proxy that provides authentication using OAuth2 providers. Versions 7.5.0 through 7.15.1 have a configuration-dependent authentication bypass. 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`; and 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. A fix has been implemented in version 7.15.2 to normalize request paths more conservatively before skip-auth matching so fragment content does not influence allowlist decisions. 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 include replacing broad rules with exact, anchored public paths and explicit HTTP methods; rejecting requests whose path contains `%23` or `#` at the ingress, load balancer, or WAF level; and/or avoiding placing sensitive application paths behind broad `skip_auth_routes` rules.

CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:H/I:L/A:N

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OAuth2 Proxy 安全漏洞

OAuth2 Proxy是OAuth2 Proxy组织的一款能够提供与Google、Github或其他提供商进行身份验证的反向代理。 OAuth2 Proxy 7.5.0版本至7.15.1版本存在安全漏洞，该漏洞源于配置相关的身份验证绕过，当使用可被攻击者控制后缀扩展的跳过身份验证规则时，可能导致未经身份验证的攻击者发送包含井号的请求，使OAuth2 Proxy匹配公共允许列表规则而后端提供受保护资源。

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