CVE-2018-6411 in Machform
Summary
by MITRE
An issue was discovered in Appnitro MachForm before 4.2.3. When the form is set to filter a blacklist, it automatically adds dangerous extensions to the filters. If the filter is set to a whitelist, the dangerous extensions can be bypassed through ap_form_elements SQL Injection.
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Analysis
by VulDB Data Team • 07/13/2025
The vulnerability identified as CVE-2018-6411 affects Appnitro MachForm versions prior to 4.2.3 and represents a critical security flaw in the form handling and file upload validation mechanisms. This issue manifests when the application employs blacklist filtering for file uploads, where the system automatically incorporates dangerous file extensions into its filter rules. However, the vulnerability becomes particularly concerning when administrators configure the system to use whitelist filtering instead, as this configuration creates an exploitable path for attackers to bypass security controls through SQL injection techniques.
The technical exploitation of this vulnerability occurs through a specific SQL injection vector within the ap_form_elements table structure. When whitelist filtering is enabled, attackers can manipulate the SQL queries that process form element configurations to inject malicious commands. This injection allows them to bypass the intended whitelist restrictions and upload files with extensions that would normally be blocked. The vulnerability stems from inadequate input validation and improper parameterization of SQL queries within the application's backend processing logic. The flaw directly relates to CWE-89 which describes SQL injection vulnerabilities where untrusted data is incorporated into SQL commands without proper sanitization or parameterization.
The operational impact of this vulnerability is severe as it enables attackers to potentially upload malicious files such as web shells, scripts, or other harmful executables to the target system. This capability can lead to complete system compromise, allowing attackers to execute arbitrary code, gain persistent access, and potentially escalate privileges within the application environment. The vulnerability affects the core file upload functionality of MachForm, which is commonly used for collecting user data through online forms, making it a particularly attractive target for attackers seeking to exploit web applications. Organizations using this software may experience unauthorized access, data breaches, and potential lateral movement within their network infrastructure.
Mitigation strategies for this vulnerability require immediate application of the vendor-provided patch to version 4.2.3 or later, which addresses the SQL injection flaw in the ap_form_elements processing. Security teams should implement comprehensive input validation for all form processing operations, ensuring that SQL queries properly utilize parameterized statements to prevent injection attacks. Additionally, organizations should review their file upload policies and implement multiple layers of validation including MIME type checking, file content analysis, and strict extension whitelisting. The remediation process should include monitoring for suspicious upload activities and implementing network-based intrusion detection systems to identify potential exploitation attempts. This vulnerability highlights the importance of following secure coding practices and adhering to the principle of least privilege in application design. The ATT&CK framework categorizes this as a technique involving command and control through file upload vulnerabilities, potentially enabling persistent threat actor access to target systems.