Remote Code Execution (RCE)

Description

Remote Code Execution (RCE) vulnerabilities occur when an application allows an attacker to execute arbitrary code remotely on the server. This can lead to complete compromise of the server, unauthorized data access, or unauthorized actions on the system.

Vulnerable Code Example

Code:

$command = $_GET['command'];
eval($command);

• The vulnerable code directly evaluates user-supplied input ($_GET['command']) using the PHP eval() function, allowing attackers to execute arbitrary PHP code on the server.
• Attackers can exploit this vulnerability by injecting malicious PHP code into the input field, potentially gaining unauthorized access or performing malicious actions on the server.

Mitigation Techniques

1. Avoid Dynamic Code Execution:
   • Avoid using functions like eval() or system() that directly execute user input as code.
   • Use safer alternatives or design patterns such as callbacks or dynamic method invocation.
2. Input Validation:
   • Validate and sanitize user input to ensure that only expected and safe values are processed.
   • Limit the scope of allowed inputs to minimize the potential impact of injection attacks.
3. Sandboxing:
   • Execute potentially risky code in isolated environments or sandboxes to limit its impact.
   • Utilize technologies like Docker containers or virtual machines for additional isolation.
4. Disable Dangerous Functions:
   • Disable dangerous functions like eval() and system() in the PHP configuration if they are not needed.
   • Implement strict security policies to restrict the usage of risky functions.

Code with Mitigation Implemented

Code:

$allowed_commands = ['command1', 'command2', 'command3'];
$command = $_GET['command'];
if (in_array($command, $allowed_commands)) {
    // Execute the command safely
    execute_command($command);
} else {
    // Handle invalid command
    echo "Invalid command";
}

• The code with mitigation avoids using eval() and instead uses alternative methods to achieve the desired functionality.
• User input is properly validated and sanitized to prevent injection of malicious code.

References

• Invicti - Remote Code Execution (RCE) - Code Injection
• PHP Manual - Variable Functions
• PHP Manual - Disable Functions