CVE-2009-4818 in Simplicity oF Upload
Summary
by MITRE
Unrestricted file upload vulnerability in upload.php in PHPSimplicity Simplicity oF Upload 1.3.2 allows remote attackers to execute arbitrary PHP code by uploading a file with a double extension, as demonstrated by .php.gif.
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Analysis
by VulDB Data Team • 08/20/2025
The vulnerability identified as CVE-2009-4818 represents a critical security flaw in the PHPSimplicity Simplicity oF Upload 1.3.2 file upload component that enables remote attackers to execute arbitrary PHP code through a carefully crafted file upload attack. This issue stems from insufficient input validation and improper file extension handling within the upload.php script, creating a pathway for malicious actors to bypass security controls and gain unauthorized code execution capabilities on the affected system.
The technical implementation of this vulnerability exploits a common weakness in web application security where the application fails to properly validate file extensions and content types during the upload process. Attackers can exploit this by creating files with double extensions such as .php.gif where the server may incorrectly interpret the file based on the last extension rather than examining the actual file content. This approach leverages the fact that many web servers and applications perform extension-based checks but do not validate the actual file type or content, allowing malicious code to be executed when the file is accessed through the web server.
From an operational perspective, this vulnerability poses significant risks to organizations using the affected software, as it provides attackers with a direct path to execute arbitrary code on the web server. The impact extends beyond simple code execution to potentially allow full system compromise, data theft, and lateral movement within the network. The vulnerability is particularly dangerous because it requires minimal effort to exploit and can be automated, making it attractive to both skilled attackers and script kiddies who seek to compromise web applications.
The attack pattern associated with CVE-2009-4818 aligns with common exploitation techniques documented in the MITRE ATT&CK framework under the T1190 technique for exploitation of remote services, specifically targeting web application vulnerabilities. This vulnerability also maps to CWE-434 which describes "Unrestricted Upload of File with Dangerous Type" and represents a classic example of insecure file upload handling that has been repeatedly identified in web applications. The attack vector demonstrates how improper input validation and lack of proper file content verification creates opportunities for privilege escalation and remote code execution.
Security mitigation strategies for this vulnerability should focus on implementing comprehensive file validation mechanisms that examine both file extensions and actual file content rather than relying solely on extension-based checks. Organizations should implement proper file type validation using MIME type checking, file content analysis, and enforce strict upload policies that prevent execution of uploaded files in web-accessible directories. Additionally, implementing proper access controls, input sanitization, and regular security audits of file upload components can significantly reduce the risk of exploitation. The most effective long-term solution involves redesigning the upload functionality to use secure file handling practices that align with established security frameworks and prevent the execution of uploaded content in web contexts.