CVE-2005-3416 in phpBB
Summary
by MITRE
phpBB 2.0.17 and earlier, when register_globals is enabled and the session_start function has not been called to handle a session, allows remote attackers to bypass security checks by setting the $_SESSION and $HTTP_SESSION_VARS variables to strings instead of arrays, which causes an array_merge function call to fail.
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Analysis
by VulDB Data Team • 06/11/2019
The vulnerability described in CVE-2005-3416 represents a critical security flaw in phpBB versions 2.0.17 and earlier that exploits a fundamental misconfiguration in session handling mechanisms. This issue specifically targets installations where the register_globals directive is enabled, creating an exploitable condition that undermines the application's authentication and authorization controls. The vulnerability stems from phpBB's improper validation of session variables, particularly when the session_start function has not been invoked to properly initialize session handling. When register_globals is enabled, PHP automatically creates global variables from request data, which creates a dangerous intersection with phpBB's session management logic that relies on specific variable types to maintain security boundaries.
The technical exploitation of this vulnerability occurs through a sophisticated manipulation of session variable types within the phpBB application's codebase. Attackers can specifically set the $_SESSION and $HTTP_SESSION_VARS variables to string values rather than the expected array structures, which fundamentally disrupts the array_merge function calls that phpBB uses to process session data. This manipulation causes the array_merge function to fail because it expects array inputs but receives strings instead, leading to a cascade of security checks that can be bypassed entirely. The flaw operates at a fundamental level within phpBB's session initialization process, where the application assumes these variables will always be arrays and does not properly validate their type before processing them. This type confusion vulnerability creates a path for attackers to circumvent authentication mechanisms that depend on proper session state management, potentially allowing unauthorized access to protected resources and administrative functions.
The operational impact of this vulnerability extends beyond simple privilege escalation to encompass complete system compromise when attackers can leverage the bypassed security checks. The vulnerability is particularly dangerous in environments where register_globals is enabled, which was common in many production servers during the time this vulnerability was prevalent. Attackers can exploit this condition to gain unauthorized access to user accounts, manipulate forum content, and potentially escalate privileges to administrative levels. The vulnerability affects the core authentication and authorization mechanisms of phpBB, making it possible for attackers to bypass user authentication entirely by manipulating session variables before proper session initialization occurs. This creates a persistent security risk that can be exploited repeatedly, as the flaw exists in the application's core session handling logic rather than in specific user-facing features or modules.
Mitigation strategies for this vulnerability require immediate implementation of multiple defensive measures to address both the immediate exploitation vector and underlying configuration issues. The most critical remediation involves disabling the register_globals directive in PHP configuration, as this setting is inherently dangerous and should never be enabled in production environments according to security best practices. System administrators must also ensure that the session_start function is properly called before any session variables are accessed or manipulated within phpBB applications. Additionally, code-level patches should be implemented to validate variable types before processing session data, specifically ensuring that $_SESSION and $HTTP_SESSION_VARS are properly validated as arrays before any array_merge operations occur. This vulnerability aligns with CWE-192, which addresses improper validation of session variables, and represents a classic example of how insecure configuration settings can create exploitable conditions that bypass application-level security controls. Organizations should also consider implementing runtime monitoring and intrusion detection systems to identify attempts to manipulate session variables in ways that could indicate exploitation attempts. The vulnerability demonstrates the critical importance of proper session management practices and the dangers of relying on insecure PHP configuration settings that were common during the era when this vulnerability was prevalent.