CVE-2018-16352 in WeaselCMS
Summary
by MITRE
There is a PHP code upload vulnerablity in WeaselCMS 0.3.6 via index.php because code can be embedded at the end of a .png file when the image/png content type is used.
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Analysis
by VulDB Data Team • 03/20/2020
The vulnerability identified as CVE-2018-16352 represents a critical file upload security flaw in WeaselCMS version 0.3.6 that stems from inadequate input validation and content type verification mechanisms. This weakness allows attackers to bypass security measures designed to prevent arbitrary code execution by embedding PHP code within image files, specifically exploiting the handling of png file uploads through the index.php endpoint. The vulnerability manifests when the application fails to properly validate the file content against its declared MIME type, creating an opportunity for malicious code injection.
The technical implementation of this vulnerability involves the manipulation of file upload processes where the system accepts image files with the image/png content type but does not perform thorough validation of the actual file content. Attackers can append PHP code to the end of legitimate png files, taking advantage of the fact that png files can contain arbitrary data beyond their standard image structure. This technique exploits the trust placed in the content type header and the assumption that files with png extensions are purely image data. The flaw resides in the application's failure to validate the actual file content against its declared type, which is a fundamental security principle that should be enforced during file upload processing. This vulnerability aligns with CWE-434 which describes insecure file upload handling, where applications accept files without proper validation of their content and type.
The operational impact of this vulnerability is severe and potentially catastrophic for systems running affected WeaselCMS versions. An attacker with access to the upload functionality can execute arbitrary PHP code on the server, potentially leading to complete system compromise, data exfiltration, and persistence mechanisms. The vulnerability enables attackers to establish backdoors, escalate privileges, or use the compromised server as a staging ground for further attacks. The attack vector is particularly dangerous because it leverages legitimate file upload functionality, making detection more challenging and allowing attackers to maintain stealth while executing malicious code. This type of vulnerability directly relates to ATT&CK technique T1059.007 which covers Scripting, specifically PHP scripting, and T1078 which covers Valid Accounts, as the attack typically requires an authenticated user with upload privileges.
Mitigation strategies for CVE-2018-16352 must address both the immediate vulnerability and implement comprehensive security controls to prevent similar issues. Organizations should implement strict file validation mechanisms that examine actual file content rather than relying solely on MIME type headers or file extensions. This includes performing binary analysis of uploaded files to ensure they match their declared types and implementing proper file type whitelisting. The recommended approach involves using dedicated libraries or tools to verify file integrity, implementing multiple validation layers, and ensuring that uploaded files are stored outside the web root or properly configured to prevent execution. Additionally, implementing proper access controls and least privilege principles can limit the impact of successful exploitation, while regular security audits and penetration testing should be conducted to identify similar vulnerabilities in other applications. The solution should also include proper logging and monitoring of file upload activities to detect suspicious behavior and implement automatic file type checking as part of the application's security architecture.