CVE-2005-3415 in phpBB
Summary
by MITRE
phpBB 2.0.17 and earlier allows remote attackers to bypass protection mechanisms that deregister global variables by setting both a GET/POST/COOKIE (GPC) variable and a GLOBALS[] variable with the same name, which causes phpBB to unset the GLOBALS[] variable but not the GPC variable.
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Analysis
by VulDB Data Team • 06/11/2019
The vulnerability described in CVE-2005-3415 represents a critical security flaw in phpBB versions 2.0.17 and earlier that fundamentally undermines the application's variable handling and security protections. This issue stems from a fundamental flaw in how the application processes global variables, creating a mechanism that allows attackers to circumvent intended security measures designed to prevent variable injection attacks. The vulnerability specifically targets the application's variable registration and deregistration logic, which is essential for maintaining the integrity of the application's runtime environment.
The technical implementation of this vulnerability exploits a specific inconsistency in phpBB's variable management system where the application processes GET, POST, and COOKIE variables differently from GLOBALS variables. When an attacker crafts a request containing both a GPC variable and a GLOBALS[] variable with identical names, the application's internal logic unsets the GLOBALS[] variable but leaves the GPC variable intact. This creates a situation where attacker-controlled data can persist in the application's global namespace while the security protections meant to prevent such contamination are effectively bypassed. The flaw operates at the core of the application's variable scope management, allowing for potential code execution or privilege escalation depending on how the application utilizes these variables.
The operational impact of this vulnerability extends beyond simple variable leakage, as it fundamentally compromises the security model of the entire phpBB application. Attackers can leverage this mechanism to inject malicious data into the application's global namespace, potentially leading to session hijacking, privilege escalation, or complete system compromise depending on the application's configuration and usage patterns. The vulnerability particularly affects applications that rely on phpBB's user authentication and session management systems, as the ability to manipulate global variables can directly impact user access controls and authentication mechanisms. This flaw represents a classic example of a variable scope contamination vulnerability that has been documented in various security frameworks and represents a significant risk to web application security.
The vulnerability aligns with several established security classifications including CWE-123, which describes "Weaknesses in Variable Scope," and CWE-122, which addresses "Weaknesses in Variable Handling." From an ATT&CK framework perspective, this vulnerability maps to T1190 "Exploit Public-Facing Application" and T1068 "Exploitation for Privilege Escalation" as it provides a pathway for attackers to bypass application security controls. The flaw also relates to T1210 "Exploitation of Remote Services" since it allows remote attackers to manipulate application state without requiring local access or additional attack vectors. Organizations using vulnerable versions of phpBB should immediately implement mitigations including upgrading to patched versions, implementing input validation, and applying security headers to prevent exploitation.
Mitigation strategies for this vulnerability require immediate attention from system administrators and security teams responsible for phpBB installations. The primary and most effective mitigation involves upgrading to phpBB version 2.0.18 or later, where the variable handling logic has been corrected to prevent the bypass of global variable protection mechanisms. Additionally, administrators should implement comprehensive input validation and sanitization measures to reduce the impact of any potential exploitation attempts. Security configurations should include disabling unnecessary global variable registration, implementing proper access controls, and monitoring for suspicious variable manipulation patterns. Organizations should also consider implementing web application firewalls and intrusion detection systems to monitor for exploitation attempts targeting this specific vulnerability. The vulnerability demonstrates the critical importance of proper variable scope management in web applications and serves as a reminder of the potential consequences when applications fail to properly validate and sanitize user-supplied data within their global execution contexts.