CVE-2006-2330 in PHP-Fusion
Summary
by MITRE
PHP-Fusion 6.00.306 and earlier, running under Apache HTTP Server 1.3.27 and PHP 4.3.3, allows remote authenticated users to upload files of arbitrary types using a filename that contains two or more extensions that ends in an assumed-valid extension such as .gif, which bypasses the validation, as demonstrated by uploading then executing an avatar file that ends in ".php.gif" and contains PHP code in EXIF metadata.
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Analysis
by VulDB Data Team • 07/30/2022
This vulnerability exists in PHP-Fusion versions 6.00.306 and earlier when deployed on Apache HTTP Server 1.3.27 with PHP 4.3.3, representing a critical server-side file upload validation bypass flaw. The vulnerability stems from insufficient input sanitization and file extension validation mechanisms within the application's avatar upload functionality. Attackers can exploit this weakness by crafting malicious filenames containing multiple extensions where the final extension appears legitimate, such as .gif, .jpg, or .png, while the preceding extension is typically a server-side executable format like .php. This technique leverages the application's failure to properly validate file extensions through comprehensive checking rather than relying solely on the final file extension.
The technical implementation of this vulnerability exploits a fundamental flaw in the file validation logic that typically checks only the final file extension against a whitelist of allowed extensions. When a user uploads a file named "malicious.php.gif", the system may accept it because the final extension .gif is in the allowed list, while the preceding .php component is ignored or improperly handled during validation. This misconfiguration creates an opportunity for attackers to execute arbitrary code on the server, as the web server will interpret the file as an image due to its .gif extension while the actual executable content remains hidden within the file's metadata or actual content.
The operational impact of this vulnerability is severe and can lead to complete system compromise, as demonstrated by the ability to upload PHP code within EXIF metadata of image files. Attackers can leverage this vulnerability to execute arbitrary commands on the server, potentially gaining full administrative control over the web application and underlying system. The attack vector requires only authenticated access to the application, making it particularly dangerous as it can be exploited by users with legitimate accounts. This vulnerability aligns with CWE-434 which describes insecure file upload vulnerabilities where applications accept files without proper validation, and represents a classic example of the ATT&CK technique T1190 - Exploit Public-Facing Application, specifically targeting the upload functionality of web applications.
The exploitation process involves creating a malicious file with a double extension such as .php.gif, .asp.jpg, or similar combinations, where the final extension appears legitimate to the upload validation system while the initial extension contains executable code. When the file is processed by the web server, it may be interpreted as an image file due to the final extension, but the actual content can contain PHP code that executes when the file is accessed. This vulnerability also demonstrates the importance of implementing proper file type detection and validation beyond simple extension checking, as relying solely on file extensions provides inadequate protection against such attacks. Organizations should implement comprehensive file validation mechanisms that verify file content, not just extensions, and should employ multiple layers of security including proper file handling, access controls, and regular security audits to prevent such exploitation scenarios.