CVE-2007-5738 in Korean GHBoard
Summary
by MITRE
The FlashUpload component in Korean GHBoard uses a client-side protection mechanism to prevent uploading of dangerous file extensions, which allows remote attackers to bypass restrictions and upload arbitrary files via a modified copy of component/flashupload/upload.html.
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Analysis
by VulDB Data Team • 10/31/2017
The vulnerability identified as CVE-2007-5738 resides within the FlashUpload component of the Korean GHBoard web application, representing a critical security flaw in file upload validation mechanisms. This component employs a client-side protection scheme designed to block uploads of potentially malicious file extensions such as .asp, .aspx, .php, and others that could execute code on the server. The fundamental weakness lies in the reliance on client-side validation, which can be easily circumvented by attackers who modify the upload interface to remove or alter the protective restrictions.
The technical implementation of this vulnerability stems from the component's failure to enforce server-side validation controls, creating a dangerous mismatch between client-side restrictions and actual server-side security measures. When an attacker modifies the component/flashupload/upload.html file to bypass the client-side checks, they can upload arbitrary files to the server without detection. This flaw directly violates security principle #3 from the OWASP Top Ten 2017, which emphasizes the importance of validating inputs and implementing robust server-side controls to prevent malicious file uploads.
The operational impact of this vulnerability extends far beyond simple unauthorized file uploads, as it provides attackers with a potential foothold for more sophisticated attacks. Once an attacker successfully uploads a malicious file, they can execute arbitrary code on the target server, potentially leading to complete system compromise. The vulnerability aligns with CWE-434, which describes the weakness of unrestricted file upload, and can be categorized under ATT&CK technique T1190 for "Exploit Public-Facing Application" and T1059 for "Command and Scripting Interpreter" when the uploaded files are executed. The attack chain typically involves initial access through the vulnerable upload functionality, followed by execution of malicious payloads that can establish persistent access or escalate privileges.
Mitigation strategies for this vulnerability require immediate implementation of robust server-side validation controls that cannot be bypassed by client-side modifications. Organizations should enforce strict file type validation on the server, implement content-type checking, and utilize whitelisting approaches for allowed file extensions. The solution must include proper file name sanitization, size limitations, and storage in non-executable directories. Additionally, implementing proper access controls and monitoring mechanisms can help detect unauthorized file upload attempts. This vulnerability demonstrates the critical importance of server-side validation as a primary defense mechanism and serves as a reminder that client-side protections should never be considered sufficient for security-critical operations. The remediation process should also include comprehensive security testing of all upload functionalities and regular security audits to prevent similar issues in other components of the web application stack.