How I found a Zero Day in W3 Schools

While using the C Compiler I decided to play around with the shell.

Link to the compiler :


int main() {
system(“ls -lra /etc/;set”);

return 0;

Summary:The provided code executes a system command to list the contents of the /etc/ directory and display the environment variables. Let’s analyze it in detail, provide a proof of concept, and suggest a fix. Code Analysis:The code snippet appears to be a simple C program that utilizes the system() function to execute a system command. The command being executed is “ls -lra /etc/;set”, which combines two commands separated by a semicolon.
The first command, ls -lra /etc/, lists the contents of the /etc/ directory in a long format, including hidden files and directories.

The second command, set, displays the environment variables.
Proof of Concept:This code can potentially introduce security risks, specifically command injection vulnerabilities. An attacker could exploit this vulnerability by manipulating user input to execute arbitrary commands on the system. For example, if an attacker provided the input “;rm -rf /”, it would result in the deletion of all files on the system. Fix:To address the security risks associated with command injection, it is crucial to implement proper input validation and sanitization. Here are some recommended steps to mitigate this vulnerability:

Avoid using the system() function to execute system commands whenever possible, as it poses a higher risk of command injection.
If command execution is necessary, thoroughly validate and sanitize any user input before incorporating it into the command.

Utilize safer alternatives, such as dedicated library functions or APIs, that provide controlled and validated methods for executing system commands.
By following these steps, you can significantly reduce the risk of command injection vulnerabilities and enhance the security of the code. Please note that this analysis is based on the provided code snippet, and a more comprehensive assessment would require additional context and code review. Disclaimer:This writeup is intended for educational purposes and to raise awareness about potential security vulnerabilities. It is important to obtain proper authorization and follow responsible disclosure practices when conducting security assessments.