CVE-2017-6413 in mod_auth_openidc
Summary
by MITRE
The "OpenID Connect Relying Party and OAuth 2.0 Resource Server" (aka mod_auth_openidc) module before 2.1.6 for the Apache HTTP Server does not skip OIDC_CLAIM_ and OIDCAuthNHeader headers in an "AuthType oauth20" configuration, which allows remote attackers to bypass authentication via crafted HTTP traffic.
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Analysis
by VulDB Data Team • 09/03/2020
The vulnerability identified as CVE-2017-6413 affects the mod_auth_openidc module, a critical component that implements OpenID Connect authentication and OAuth 2.0 resource server functionality within the Apache HTTP Server ecosystem. This module serves as a bridge between Apache and identity providers, enabling single sign-on capabilities and secure API access control. The flaw exists in versions prior to 2.1.6 and represents a significant security weakness that undermines the fundamental authentication mechanisms designed to protect web applications. The vulnerability specifically targets the handling of HTTP headers within the OAuth 2.0 authentication context, creating a pathway for malicious actors to circumvent the intended security controls.
The technical root cause of this vulnerability stems from improper header processing within the authentication flow. When configured with AuthType oauth20, the module fails to properly filter or skip specific headers that begin with OIDC_CLAIM_ and OIDCAuthNHeader prefixes. These headers are typically used internally by the module to store authentication claims and user information during the OpenID Connect process. However, due to the flawed implementation, attackers can craft HTTP requests that include these headers with arbitrary values, effectively allowing them to inject false authentication data. This behavior violates the principle of least privilege and creates an authentication bypass condition that can be exploited remotely without requiring valid credentials or session tokens.
The operational impact of this vulnerability extends beyond simple authentication bypass to potentially enable full system compromise. An attacker who successfully exploits this vulnerability can gain unauthorized access to protected resources that should only be accessible to authenticated users. This weakness particularly affects web applications that rely on mod_auth_openidc for securing API endpoints, user portals, and sensitive data access points. The remote nature of the exploit means that attackers can target vulnerable systems from anywhere on the internet, making this vulnerability particularly dangerous for organizations with publicly accessible web services. The implications are further exacerbated by the fact that many organizations may not regularly audit their Apache configurations, leaving systems vulnerable for extended periods.
Organizations should prioritize immediate mitigation by upgrading to mod_auth_openidc version 2.1.6 or later, which contains the necessary patches to address the header filtering issue. Additionally, administrators should implement comprehensive monitoring of authentication headers to detect potential exploitation attempts. Security teams should conduct thorough audits of all Apache configurations using this module to ensure proper header handling and prevent unauthorized access to protected resources. The vulnerability aligns with CWE-284, which addresses improper access control, and represents a specific instance of privilege escalation through header manipulation. From an ATT&CK framework perspective, this vulnerability maps to T1078, which covers valid accounts and T1566, related to credential harvesting, as attackers can leverage the bypass to access systems that would normally require proper authentication. Organizations should also consider implementing additional security controls such as rate limiting, IP whitelisting, and enhanced logging to detect and prevent exploitation attempts.