CVE-2006-2158 in Guestbook Script
Summary
by MITRE
Dynamic variable evaluation vulnerability in index.php in Stadtaus Guestbook Script 1.7 and earlier, when register_globals is enabled, allows remote attackers to modify arbitrary program variables via parameters, which are evaluated as PHP variable variables, as demonstrated by performing PHP remote file inclusion using the include_files array parameter.
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Analysis
by VulDB Data Team • 06/18/2019
The CVE-2006-2158 vulnerability represents a critical dynamic variable evaluation flaw in the Stadtaus Guestbook Script version 1.7 and earlier, which exploits the dangerous combination of register_globals functionality with improper input validation. This vulnerability specifically targets the index.php file and demonstrates how legacy PHP configurations can create severe security risks when combined with insecure coding practices. The flaw occurs when the register_globals directive is enabled in the PHP configuration, which automatically creates global variables from HTTP request parameters, effectively bypassing normal variable scoping rules and creating an environment where attacker-controlled data can be directly injected into the application's variable namespace.
The technical implementation of this vulnerability relies on PHP's variable variable feature, where variables can be dynamically created and referenced using other variables as their names. When register_globals is enabled, parameters from HTTP requests become automatically available as global variables within the script's scope. Attackers can manipulate the include_files array parameter to inject malicious values that get evaluated as PHP variable variables, allowing them to manipulate the application's internal state and execute arbitrary code. This particular weakness enables remote attackers to perform PHP remote file inclusion attacks by leveraging the dynamic variable evaluation mechanism to load and execute malicious code from remote servers, effectively transforming a simple parameter manipulation into a full remote code execution capability.
The operational impact of this vulnerability extends far beyond simple data manipulation, as it provides attackers with complete control over the affected system's execution environment. When successfully exploited, the vulnerability allows attackers to execute arbitrary PHP code on the server, potentially leading to complete system compromise, data exfiltration, and persistence mechanisms. The attack vector is particularly dangerous because it requires minimal privileges to exploit and can be automated, making it attractive to malicious actors seeking to establish persistent access to vulnerable systems. The vulnerability also demonstrates how legacy PHP security configurations can create dangerous attack surfaces when combined with insecure coding practices, highlighting the importance of proper input validation and secure coding standards.
Mitigation strategies for this vulnerability must address both the immediate exploitation vector and the underlying architectural issues that enabled the flaw. The most effective immediate solution involves disabling the register_globals directive in the PHP configuration, which eliminates the automatic creation of global variables from HTTP parameters and prevents the vulnerability from being exploited through parameter manipulation. Additionally, developers should implement proper input validation and sanitization techniques, ensuring that all user-supplied data is properly filtered before being used in dynamic variable evaluations. The vulnerability aligns with CWE-95, which describes improper neutralization of directives in dynamically evaluated code, and maps to ATT&CK technique T1059.007 for PHP remote file inclusion attacks, emphasizing the need for comprehensive security measures including input validation, secure coding practices, and proper configuration management to prevent similar vulnerabilities from being exploited in modern applications.