CVE-2017-14346 in Blog
Summary
by MITRE
upload.php in tianchoy/blog through 2017-09-12 allows unrestricted file upload and PHP code execution by using the image/jpeg, image/pjpeg, image/png, or image/gif content type for a .php file.
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Analysis
by VulDB Data Team • 11/15/2019
The vulnerability identified as CVE-2017-14346 resides in the upload.php component of the tianchoy/blog web application, which was vulnerable through September 12, 2017. This issue represents a critical security flaw that enables attackers to bypass file upload restrictions and execute arbitrary PHP code on the target system. The vulnerability stems from insufficient validation of file content types during the upload process, specifically when handling image file formats such as jpeg, pjpeg, png, and gif. Attackers can exploit this weakness by renaming malicious PHP files with these image extensions while maintaining the actual PHP code within the file content, effectively circumventing the intended file type restrictions.
The technical implementation of this vulnerability allows for unrestricted file upload operations where the application fails to properly verify the actual content of uploaded files against their declared MIME types. When a user uploads a file with a content type of image/jpeg, image/pjpeg, image/png, or image/gif, the system accepts the file without performing proper validation checks on the file's actual binary content. This misconfiguration creates a pathway for attackers to upload PHP files that contain malicious code, which can then be executed by the web server when accessed through the application's web interface. The flaw operates at the application layer and directly violates secure coding principles related to input validation and file handling.
The operational impact of this vulnerability is severe and far-reaching, as it provides attackers with complete code execution privileges on the affected server. Successful exploitation can lead to full system compromise, data exfiltration, and persistent access to the target environment. Attackers can upload web shells, backdoors, or other malicious payloads that enable them to perform arbitrary commands, establish reverse shells, and maintain long-term access to the compromised system. This vulnerability directly maps to CWE-434, which describes insecure file upload scenarios where applications accept files without proper validation of their content. The risk is amplified by the fact that the vulnerability affects a widely used blogging platform, potentially exposing numerous installations to remote code execution attacks.
Mitigation strategies for this vulnerability should focus on implementing robust file upload validation mechanisms that go beyond simple MIME type checking. Organizations should enforce strict file type validation by examining the actual file content rather than relying solely on client-provided headers or extensions. The recommended approach includes implementing content-based file validation using magic number detection, rejecting files with executable extensions, and storing uploaded files outside the web root directory. Additionally, proper access controls should be implemented to ensure that uploaded files cannot be executed directly by the web server. This vulnerability aligns with ATT&CK technique T1190, which covers the exploitation of vulnerabilities in web applications to gain code execution capabilities, and demonstrates the critical importance of input validation in preventing file upload related attacks.