CWE-161: Improper Neutralization of Multiple Leading Special Elements

What is Improper Neutralization of Multiple Leading Special Elements?

• Overview: This vulnerability occurs when a software product fails to properly handle multiple leading special elements in input data. These elements aren't neutralized correctly, leading to unexpected behavior when the data is processed by another component.

• Exploitation Methods:

• Attackers can exploit this by crafting input data with multiple leading special characters to manipulate the way the data is interpreted by the downstream component.
• Common techniques include injection attacks where special characters alter the intended command or query structure.

• Security Impact:

• Direct consequences include unauthorized execution of commands or queries, data corruption, or exposure of sensitive information.
• Potential cascading effects might involve compromised system integrity, allowing further exploitation or lateral movement within a network.
• Business impact can range from data breaches and financial loss to reputational damage and legal liabilities.

• Prevention Guidelines:

• Implement thorough input validation and sanitation routines that neutralize multiple leading special elements before processing.
• Follow security best practices such as using parameterized queries and prepared statements to avoid injection vulnerabilities.
• Utilize recommended tools and frameworks that automatically handle input sanitization, such as web application firewalls (WAFs) and secure coding libraries.

Corgea can automatically detect and fix Improper Neutralization of Multiple Leading Special Elements in your codebase. [Try Corgea free today](https://corgea.app).

Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

const { exec } = require('child_process');

function executeCommand(userInput) {
    // Vulnerable code: does not properly neutralize multiple leading special elements
    // An attacker can exploit this by sending input like "&& rm -rf /"
    // This input will be executed by the shell, leading to potential system compromise
    exec(`ls \${userInput}`, (error, stdout, stderr) => {
        if (error) {
            console.error(`exec error: \${error}`);
            return;
        }
        console.log(`stdout: \${stdout}`);
    });
}

executeCommand("&& rm -rf /");

How to fix Improper Neutralization of Multiple Leading Special Elements?

To fix this vulnerability, you should validate and sanitize the user input to remove any leading special elements that could be misinterpreted by the shell. This includes stripping characters like slashes, ampersands, and semicolons. Additionally, using safer APIs like execFile or spawn from the child_process module, which do not invoke a shell, can prevent the execution of unintended commands.

Fixed Code Example

const { execFile } = require('child_process');

function executeCommand(userInput) {
    // Fixed code: sanitize input by stripping leading special characters
    // This prevents shell injection by removing dangerous characters from the start
    const sanitizedInput = userInput.replace(/^[\/&;]+/, '');
    // Use execFile which does not invoke a shell, thus avoiding shell interpretation
    execFile('ls', [sanitizedInput], (error, stdout, stderr) => {
        if (error) {
            console.error(`execFile error: \${error}`);
            return;
        }
        console.log(`stdout: \${stdout}`);
    });
}

executeCommand("&& rm -rf /");

In both examples, the key is to sanitize user input and use safer command execution methods that avoid shell interpretation, thus mitigating the risk of executing unintended commands due to improperly neutralized leading special elements. The fixed example demonstrates how to properly sanitize inputs and use execFile to prevent shell command injection vulnerabilities.