CVE-2006-5863 in LetterIt
Summary
by MITRE
PHP remote file inclusion vulnerability in inc/session.php for LetterIt 2 allows remote attackers to execute arbitrary PHP code via a URL in the lang parameter.
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Analysis
by VulDB Data Team • 04/27/2026
The vulnerability described in CVE-2006-5863 represents a critical remote file inclusion flaw affecting the LetterIt 2 web application. This issue resides within the inc/session.php file where the application fails to properly validate user-supplied input before incorporating it into file inclusion operations. The vulnerability specifically manifests when the lang parameter is manipulated by an attacker to reference external URLs, enabling arbitrary code execution on the target system. The flaw stems from improper input sanitization and the application's reliance on user-provided data without adequate validation mechanisms.
This vulnerability operates under the broader category of insecure direct object references and remote code execution threats, with direct implications for the principle of least privilege and input validation. The technical implementation allows attackers to inject malicious URLs through the lang parameter, which are then processed by the PHP include or require functions. When these functions execute with attacker-controlled input, they can load and execute remote PHP scripts, effectively granting unauthorized code execution capabilities. The vulnerability's classification aligns with CWE-98 and CWE-88, specifically addressing weaknesses in PHP's file inclusion mechanisms and improper input validation.
The operational impact of this vulnerability is severe as it enables attackers to gain complete control over the affected web server. Once exploited, adversaries can execute arbitrary commands, access sensitive data, modify application functionality, and potentially establish persistent backdoors. The remote nature of the attack means that exploitation does not require local system access, making it particularly dangerous for web applications. The vulnerability affects the confidentiality, integrity, and availability of the target system, representing a significant threat to organizational security posture. This flaw directly impacts the application's security controls and can lead to data breaches, system compromise, and unauthorized access to sensitive information.
Mitigation strategies for this vulnerability should include immediate patching of the LetterIt 2 application to address the file inclusion flaw. Organizations must implement proper input validation and sanitization techniques to prevent malicious URLs from being processed by the application. The recommended approach involves using allowlists for parameter values, implementing proper URL validation, and avoiding dynamic file inclusion with user-supplied data. Security measures should also include restricting file inclusion operations to local paths only and implementing web application firewalls to detect and block suspicious URL patterns. Additionally, the principle of least privilege should be enforced by ensuring that web applications run with minimal required permissions and that input parameters are properly escaped before processing. This vulnerability serves as a reminder of the critical importance of secure coding practices and input validation in preventing remote code execution attacks, with implications for the broader security community's understanding of PHP application security.