CVE-2007-6527 in PunBB
Summary
by MITRE
uploadimg.php in the Automatic Image Upload with Thumbnails (imgUpload) module 1.3.2 for PunBB only verifies the Content-type field of uploaded files, which allows remote attackers to upload and execute arbitrary content via a file with a (1) JPG, (2) GIF, or (3) PNG MIME type.
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Analysis
by VulDB Data Team • 09/13/2018
The vulnerability described in CVE-2007-6527 represents a critical security flaw in the imgUpload module version 1.3.2 for PunBB forums, specifically within the uploadimg.php script. This issue stems from an inadequate file validation mechanism that relies solely on the Content-type header field provided by the client during file upload operations. The vulnerability is classified under CWE-434 which addresses the insecure upload of executable files, making it particularly dangerous in web application contexts where user-uploaded content is processed and stored.
The technical implementation of this flaw allows attackers to bypass security checks by manipulating the MIME type header of malicious files. When an attacker uploads a file with a legitimate image extension such as .jpg, .gif, or .png but modifies the Content-type header to match these image types, the system incorrectly assumes the file is safe for execution. This vulnerability specifically affects the image upload functionality that processes thumbnail generation, creating a path for arbitrary code execution when the malicious file is later processed or served. The flaw demonstrates a classic case of insufficient input validation and improper file type verification.
The operational impact of this vulnerability is severe as it enables remote code execution capabilities for attackers who can upload malicious files disguised as images. This allows for complete system compromise through various attack vectors including web shell deployment, database manipulation, or privilege escalation. The vulnerability affects the core functionality of PunBB forums where users can upload images, making it a persistent threat that could be exploited by unauthorized users to gain administrative access or disrupt service availability. Attackers can leverage this weakness to establish persistent access points within the forum infrastructure.
Mitigation strategies for this vulnerability should focus on implementing robust file validation mechanisms that go beyond Content-type header checking. Organizations should implement multiple validation layers including file extension verification, file signature checking, and binary content analysis to ensure uploaded files match their claimed MIME types. The solution must address the fundamental flaw in the imgUpload module by requiring server-side validation of actual file content rather than trusting client-provided metadata. Additionally, implementing proper file access controls, restricting upload permissions to authenticated users only, and monitoring upload activities can significantly reduce the risk of exploitation. This vulnerability aligns with ATT&CK technique T1505.003 which covers "Obfuscated Files or Information" and T1059.007 which addresses "Command and Scripting Interpreter: JavaScript" in contexts where malicious files are uploaded and executed through web applications.