CVE-2018-17418 in Monstra
Summary
by MITRE
Monstra CMS 3.0.4 allows remote attackers to execute arbitrary PHP code via a mixed-case file extension, as demonstrated by the 123.PhP filename, because plugins\box\filesmanager\filesmanager.admin.php mishandles the forbidden_types variable.
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Analysis
by VulDB Data Team • 07/29/2023
The vulnerability CVE-2018-17418 represents a critical remote code execution flaw in Monstra CMS version 3.0.4 that exploits improper file extension validation mechanisms. This vulnerability specifically targets the file management functionality within the CMS, where the system fails to properly sanitize file extensions that contain mixed case characters. The attack vector is particularly insidious because it leverages the fact that the system does not perform case-sensitive validation on file extensions, allowing malicious actors to bypass security controls through seemingly innocuous filenames such as "123.PhP" where the php extension is capitalized.
The technical root cause of this vulnerability lies in the improper handling of the forbidden_types variable within the plugins/box/filesmanager/filesmanager.admin.php file. This file contains the logic for managing file uploads and validation, but fails to implement comprehensive sanitization of file extensions before processing. The vulnerability manifests when the system accepts files with mixed-case extensions that should be blocked by the forbidden_types configuration but are not properly filtered due to case-insensitive matching logic. This flaw directly maps to CWE-434, which describes insecure file upload vulnerabilities where applications fail to properly validate file types and extensions.
The operational impact of this vulnerability is severe as it provides remote attackers with arbitrary code execution capabilities on the affected system. An attacker can upload malicious PHP files with mixed-case extensions that bypass the security controls, allowing them to execute arbitrary code with the privileges of the web server. This creates a complete compromise of the CMS installation, enabling attackers to access sensitive data, modify content, establish persistent backdoors, or use the compromised system as a launch point for further attacks within the network infrastructure. The vulnerability affects the integrity and confidentiality of the entire CMS environment, potentially leading to data breaches and unauthorized access to user information.
Mitigation strategies for CVE-2018-17418 should include immediate patching of the Monstra CMS to version 3.0.5 or later where this vulnerability has been addressed. Organizations should also implement additional security measures such as restricting file upload capabilities to only allow specific, safe file types and implementing strict case-sensitive validation of file extensions. The system should enforce proper input sanitization and validation at multiple layers, including both client-side and server-side checks. Security teams should monitor file upload directories for suspicious activity and implement proper access controls to limit the privileges of the web server process. This vulnerability aligns with ATT&CK technique T1190 for exploiting vulnerabilities in web applications and T1059 for executing malicious code, making it a critical target for both defensive and offensive security operations.