CVE-2016-2049 in PHP OpenID Library
Summary
by MITRE
examples/consumer/common.php in JanRain PHP OpenID library (aka php-openid) improperly checks the openid.realm parameter against the SERVER_NAME element in the SERVER superglobal array, which might allow remote attackers to hijack the authentication of arbitrary users via vectors involving a crafted HTTP Host header.
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Analysis
by VulDB Data Team • 07/13/2018
The vulnerability identified as CVE-2016-2049 resides within the JanRain PHP OpenID library, specifically in the examples/consumer/common.php file where the implementation fails to properly validate the openid.realm parameter against the SERVER_NAME element in the SERVER superglobal array. This flaw represents a critical security weakness in the OpenID authentication mechanism that could enable remote attackers to manipulate the authentication flow and potentially hijack user sessions. The issue stems from an inadequate validation process that does not sufficiently verify the authenticity of the realm parameter, creating an opportunity for attackers to exploit the trust relationship established during OpenID authentication.
The technical flaw manifests when the library processes the openid.realm parameter by comparing it against the SERVER_NAME element without proper sanitization or comprehensive validation checks. This vulnerability is particularly dangerous because it allows attackers to craft malicious HTTP Host headers that can bypass the intended security measures. The improper validation occurs at the application level where the library fails to implement robust input validation mechanisms that would normally be expected in secure authentication systems. This type of vulnerability falls under CWE-284 Access Control, specifically related to inadequate access control mechanisms that allow unauthorized users to manipulate system behavior.
The operational impact of this vulnerability is significant as it enables man-in-the-middle attacks and session hijacking scenarios where attackers can redirect authentication flows to malicious domains. Remote attackers can exploit this weakness by crafting HTTP requests with manipulated Host headers that cause the OpenID library to accept forged realm parameters, thereby allowing them to intercept and potentially manipulate user authentication tokens. This vulnerability directly impacts the integrity and authenticity of the OpenID authentication process, potentially allowing attackers to impersonate legitimate users and gain unauthorized access to protected resources. The attack vector is particularly concerning because it operates at the HTTP protocol level and can be executed without requiring any special privileges or local access to the target system.
Organizations using the affected php-openid library should immediately implement mitigations including updating to patched versions of the library, implementing proper input validation for all OpenID parameters, and configuring web servers to properly handle Host header validation. The recommended approach involves implementing comprehensive validation checks that verify the realm parameter against multiple sources including the actual request URI, proper hostname validation, and implementing strict access control policies. Security teams should also consider implementing network-level controls such as firewall rules that restrict access to OpenID endpoints and monitor for suspicious Host header patterns. This vulnerability aligns with ATT&CK technique T1566 Credential Access through manipulation of authentication flows and represents a classic example of how improper input validation can lead to authentication bypass scenarios. The mitigation strategy should include thorough code review processes to identify similar validation weaknesses and implementation of defense-in-depth measures that protect against multiple attack vectors.