CVE-2006-1895 in phpBB
Summary
by MITRE
Direct static code injection vulnerability in includes/template.php in phpBB allows remote authenticated users with write access to execute arbitrary PHP code by modifying a template in a way that (1) bypasses a loose ".*" regular expression to match BEGIN and END statements in overall_header.tpl, or (2) is used in an eval statement by includes/bbcode.php for bbcode.tpl.
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Analysis
by VulDB Data Team • 07/24/2018
The vulnerability identified as CVE-2006-1895 represents a critical direct static code injection flaw within the phpBB bulletin board system that fundamentally compromises the security posture of affected installations. This vulnerability exists in the template processing mechanisms of phpBB, specifically within the includes/template.php file, creating a pathway for authenticated attackers to execute arbitrary PHP code on vulnerable systems. The flaw stems from inadequate input validation and sanitization within the template parsing logic, allowing malicious users with write permissions to inject malicious code that gets executed during template rendering processes.
The technical implementation of this vulnerability exploits two distinct attack vectors that leverage different aspects of phpBB's template handling architecture. The first vector involves bypassing a loose regular expression pattern matching mechanism that is designed to validate BEGIN and END statements within template files such as overall_header.tpl. This loose pattern matching fails to properly validate template syntax, allowing attackers to inject malformed template constructs that evade detection while still maintaining the structural integrity required for code execution. The second attack vector utilizes the eval statement processing within includes/bbcode.php for handling bbcode.tpl files, where malicious template content gets directly evaluated as PHP code without proper sanitization. Both attack paths demonstrate a fundamental failure in input validation and code execution isolation within the phpBB template engine.
The operational impact of this vulnerability extends far beyond simple code execution capabilities, as it provides authenticated attackers with complete control over affected systems. Since the vulnerability requires only write access to template files, it can be exploited by users who have been granted basic administrative privileges or even regular user accounts with template modification permissions. This means that attackers can escalate their privileges and potentially compromise entire installations through simple template modifications. The vulnerability creates a persistent backdoor mechanism that can be used for data exfiltration, system reconnaissance, and further lateral movement within compromised networks, making it particularly dangerous for organizations relying on phpBB for community forums or internal communication platforms.
Organizations affected by this vulnerability should implement immediate mitigations including restricting write permissions for template files to only trusted administrators, implementing comprehensive input validation for all template modifications, and deploying web application firewalls to monitor for suspicious template content patterns. The vulnerability aligns with CWE-94, which describes improper validation of code in interpreted languages, and specifically maps to ATT&CK technique T1059.007 for execution through PHP code injection. Additionally, the vulnerability demonstrates characteristics of CWE-20, or improper input validation, and CWE-74, or injection flaws, making it a multi-faceted security weakness that requires layered defensive measures. Regular security audits of template handling mechanisms and implementation of automated template content scanning should be prioritized to prevent similar vulnerabilities in future deployments.