CVE-2021-41646 in Online Reviewer System
Summary
by MITRE • 10/29/2021
Remote Code Execution (RCE) vulnerability exists in Sourcecodester Online Reviewer System 1.0 by uploading a maliciously crafted PHP file that bypasses the image upload filters..
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Analysis
by VulDB Data Team • 04/15/2026
The CVE-2021-41646 vulnerability represents a critical remote code execution flaw in the Sourcecodester Online Reviewer System version 1.0, demonstrating a classic insecure file upload vulnerability that enables attackers to execute arbitrary code on the target system. This vulnerability stems from inadequate input validation and filtering mechanisms within the application's file upload functionality, specifically targeting the image upload component that should ostensibly only accept image files. The flaw allows malicious actors to bypass security measures by uploading PHP files that contain executable code, effectively transforming the legitimate file upload feature into a backdoor for system compromise.
The technical implementation of this vulnerability involves a combination of file extension checking bypass techniques and file content inspection evasion. Attackers can craft PHP files with extensions that appear to be valid image formats such as .jpg or .png while simultaneously containing PHP code within the file content that executes when the file is accessed through the web server. This type of vulnerability falls under CWE-434 which specifically addresses insecure file uploads where applications accept files from untrusted sources without proper validation. The vulnerability exploits the principle of least privilege by allowing unrestricted file execution capabilities through what should be a restricted upload interface, creating an attack surface that directly violates secure coding practices.
The operational impact of CVE-2021-41646 extends far beyond simple code execution, as it provides attackers with complete control over the affected system. Once successfully exploited, adversaries can establish persistent access, escalate privileges, exfiltrate sensitive data, and potentially use the compromised system as a launch point for further attacks within the network infrastructure. The vulnerability's remote nature means that exploitation can occur from anywhere on the internet without requiring physical access to the target network, making it particularly dangerous for web applications that are publicly accessible. From an ATT&CK framework perspective, this vulnerability maps to T1190 (Exploit Public-Facing Application) and T1059.007 (Command and Scripting Interpreter: PHP), demonstrating how attackers can leverage application weaknesses to achieve their objectives.
Mitigation strategies for CVE-2021-41646 must address both the immediate vulnerability and broader security architecture concerns. Organizations should implement strict file type validation using whitelisting approaches rather than blacklisting, ensure that uploaded files are stored outside the web root directory, and employ proper file content verification mechanisms that examine actual file signatures rather than relying solely on extensions. The application should also implement robust access controls and file permissions that prevent execution of uploaded content, while regular security testing including dynamic application security testing and manual penetration testing should be conducted to identify similar vulnerabilities. Additionally, implementing web application firewalls and security headers can provide additional layers of protection against exploitation attempts, and regular security updates should be applied to address known vulnerabilities in the application and underlying infrastructure components.