CVE-2018-16731 in CScms
Summary
by MITRE
CScms 4.1 allows arbitrary file upload by (for example) adding the php extension to the default filetype list (gif, jpg, png), and then providing a .php pathname within fileurl JSON data.
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Analysis
by VulDB Data Team • 03/21/2020
The vulnerability identified as CVE-2018-16731 affects CScms 4.1, a content management system that suffers from a critical arbitrary file upload flaw. This vulnerability stems from insufficient input validation and inadequate file type restrictions within the system's upload functionality. Attackers can exploit this weakness by manipulating the default filetype whitelist which typically includes gif, jpg, and png extensions, thereby enabling the upload of malicious PHP files that can execute arbitrary code on the target server.
The technical implementation of this vulnerability involves modifying the fileurl JSON data to include a .php extension within the pathname, effectively bypassing the intended file type restrictions. This flaw represents a classic case of insecure file upload handling where the application fails to properly validate file extensions or content, allowing attackers to upload web shells or other malicious scripts that can be executed within the web server context. The vulnerability specifically targets the JSON data processing mechanism where file paths are constructed, creating a path traversal and code execution vector.
From an operational perspective, this vulnerability presents a severe risk to affected systems as it allows remote attackers to achieve persistent code execution on the web server. Once successfully exploited, attackers can establish backdoors, exfiltrate sensitive data, escalate privileges, or use the compromised system as a launch point for further attacks within the network. The impact extends beyond simple code execution to include potential data breaches, system compromise, and service disruption. This vulnerability aligns with CWE-434 which describes insecure file upload scenarios where applications accept files without proper validation of their content or type.
The exploitation of this vulnerability typically follows the pattern of modifying JSON data structures to include malicious file extensions, often through API endpoints or administrative interfaces that handle file uploads. Attackers may leverage this to upload web shells, reverse shells, or other malicious payloads that can be triggered through web requests. The attack surface is particularly concerning because it allows for automated exploitation and can be combined with other vulnerabilities to achieve full system compromise. This type of vulnerability is categorized under the attack techniques described in the MITRE ATT&CK framework, specifically related to Initial Access and Execution phases where adversaries gain entry and establish persistence.
Mitigation strategies for CVE-2018-16731 should include immediate patching of the affected CScms version, implementing robust file type validation that checks both file extensions and content signatures, and restricting file upload capabilities to authenticated users only. Organizations should also implement proper input sanitization, enforce strict file naming conventions, and deploy web application firewalls to detect and block suspicious upload attempts. Additional security measures include disabling unnecessary upload features, implementing proper access controls, and conducting regular security assessments to identify similar vulnerabilities in other applications and systems. The remediation process should also include monitoring for any signs of exploitation and implementing proper logging mechanisms to track file upload activities.