How does the payload exploit the 'file_get_contents()' function?

The payload exploits the file_get_contents() function by injecting it into a vulnerable PHP application through a crafted URL. Here's how it works:

Breakdown of the Payload

The payload in the example is:

http://localhost:82/codeexec/example1.php?name=hacker%22;var_dump(file_get_contents(%20%27/etc/passwd%27));//

Steps of Exploitation

1. Vulnerable Application: The PHP script at example1.php is vulnerable because it uses user input ($_GET['name']) in a way that allows for code execution (e.g., through eval() or similar functions).

2. Injection of Code: The payload includes:

   • hacker%22; which translates to hacker"; when decoded. The "; is used to terminate the string that the application is processing.
   • var_dump(file_get_contents(%20%27/etc/passwd%27)); is the injected code that will be executed. This part reads the contents of the /etc/passwd file, which contains user account information on Unix-like systems.

3. Execution of the Payload: When the PHP script processes this input, it effectively executes the injected code:

   • The file_get_contents('/etc/passwd') function reads the contents of the specified file.
   • var_dump() is then used to display the contents of that file.

4. Output of Sensitive Information: The result of the payload execution is that the contents of the /etc/passwd file are displayed in the response. This file can provide valuable information about user accounts on the system, which can be used for further exploitation.

Conclusion

The payload exploits the file_get_contents() function by injecting it into the vulnerable application, allowing an attacker to read sensitive files on the server. This demonstrates the importance of validating and sanitizing user input to prevent such code injection vulnerabilities.