CVE-2021-24236 in Imagements Plugin
Summary
by MITRE • 05/06/2021
The Imagements WordPress plugin through 1.2.5 allows images to be uploaded in comments, however only checks for the Content-Type in the request to forbid dangerous files. This allows unauthenticated attackers to upload arbitrary files by using a valid image Content-Type along with a PHP filename and code, leading to RCE.
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Analysis
by VulDB Data Team • 05/09/2021
The CVE-2021-24236 vulnerability affects the Imagements WordPress plugin version 1.2.5 and earlier, presenting a critical security flaw that enables unauthorized remote code execution through improper file validation mechanisms. This vulnerability specifically targets the plugin's comment image upload functionality, where the system relies solely on Content-Type header verification rather than comprehensive file type checking. The flaw demonstrates a fundamental security oversight in the plugin's input validation process, creating an exploitable condition that can be leveraged by unauthenticated attackers to compromise affected WordPress installations.
The technical implementation of this vulnerability stems from the plugin's insufficient validation approach that accepts any file with a legitimate image Content-Type header regardless of the actual file content or extension. Attackers can exploit this by crafting malicious files with PHP extensions such as .php, .phtml, or .php3 while maintaining valid image Content-Type headers like image/jpeg or image/png. This technique bypasses the plugin's security controls by exploiting the trust placed in the Content-Type field, which can be easily manipulated in HTTP requests. The vulnerability operates at the application layer and represents a classic case of insecure file upload validation, which is classified under CWE-434 as "Unrestricted Upload of File with Dangerous Type."
The operational impact of this vulnerability is severe and far-reaching for WordPress administrators and users who have the Imagements plugin installed. An unauthenticated attacker can upload malicious PHP files through comment submissions, potentially gaining full control over the affected web server. This remote code execution capability allows attackers to execute arbitrary commands on the server, install backdoors, steal sensitive data, modify website content, or use the compromised server for further attacks. The vulnerability affects not only the immediate plugin functionality but also poses risks to the entire WordPress installation, potentially compromising user data, website integrity, and server security. According to ATT&CK framework, this vulnerability maps to T1059.007 for Command and Scripting Interpreter and T1505.003 for Server Software Component, demonstrating the multi-faceted attack surface this flaw creates.
Mitigation strategies for CVE-2021-24236 should include immediate plugin updates to version 1.2.6 or later, which addresses the validation issue through enhanced file type checking and content verification. Administrators should implement additional security measures such as restricting file upload capabilities, implementing proper file extension validation, and configuring web server-level restrictions to prevent execution of PHP files in upload directories. Network-level protections including web application firewalls and intrusion detection systems can help detect and block malicious upload attempts. Regular security audits and monitoring of file upload functionalities are essential for identifying similar validation flaws in other plugins or custom applications. The vulnerability also underscores the importance of following secure coding practices, particularly regarding input validation, and adhering to security standards such as those outlined in the OWASP Top Ten and NIST cybersecurity guidelines for preventing insecure file upload vulnerabilities.