CVE-2009-4451 in kandalf upper
Summary
by MITRE
Unrestricted file upload vulnerability in upper.php in kandalf upper 0.1 allows remote attackers to execute arbitrary code by uploading a file with an executable extension, then accessing it via a direct request to the file in fileup/.
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Analysis
by VulDB Data Team • 06/25/2025
The vulnerability identified as CVE-2009-4451 represents a critical unrestricted file upload flaw within the kandalf upper 0.1 web application. This vulnerability exists in the upper.php script which processes file uploads without adequate validation or sanitization mechanisms. The flaw allows remote attackers to bypass security controls and upload malicious files with executable extensions directly to the server. The vulnerability specifically affects the fileup/ directory where uploaded files are stored, creating a pathway for arbitrary code execution when these files are subsequently accessed through direct HTTP requests.
The technical nature of this vulnerability aligns with CWE-434, which describes unrestricted upload of executable code, and represents a classic example of insufficient input validation in web applications. The flaw stems from the application's failure to implement proper file type checking, extension validation, or content verification mechanisms. Attackers can exploit this by uploading files with extensions such as .php, .asp, .jsp, or other server-side script extensions that will be executed by the web server when accessed. The vulnerability does not require authentication or specific user privileges, making it particularly dangerous as it can be exploited by any remote attacker with access to the upload functionality.
The operational impact of this vulnerability is severe and encompasses multiple attack vectors within the cybersecurity landscape. An attacker who successfully exploits this vulnerability can achieve arbitrary code execution on the target server, potentially leading to complete system compromise. This allows for privilege escalation, data exfiltration, lateral movement within the network, and establishment of persistent backdoors. The vulnerability enables techniques categorized under ATT&CK matrix tactics such as TA0002 (Execution), TA0006 (Credential Access), and TA0004 (Privilege Escalation). The attack surface is broad as it affects not only the immediate web application but also potentially the entire underlying server infrastructure, including operating system components, databases, and network services.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security architecture improvements. The most critical immediate action involves implementing strict file type validation and extension filtering in the upper.php script, ensuring that only safe file types are accepted for upload. This includes maintaining a whitelist of approved extensions and rejecting any files with executable extensions. Additionally, uploaded files should be stored in a location that is not directly accessible via the web server, or the web server should be configured to prevent execution of uploaded files. The application should also implement proper file content verification, such as MIME type checking and file signature validation, to prevent the upload of disguised malicious files. Organizations should implement the principle of least privilege for file upload directories and ensure that uploaded files are properly sanitized and scanned for malicious content before being made available to users. Regular security assessments and code reviews should be conducted to identify and remediate similar vulnerabilities in other components of the application stack, following established security frameworks and standards.