CWE-74: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')

What is Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')?

• Overview: Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection') occurs when a software application constructs commands or data structures using input that comes from an upstream source without adequately neutralizing special elements. These elements could be interpreted in unintended ways by the downstream component, leading to potential injection vulnerabilities.

• Exploitation Methods:

• Attackers exploit this vulnerability by injecting specially crafted inputs that manipulate the downstream component’s parsing or execution logic.
• Common attack patterns include SQL injection, command injection, and XML injection, where malicious code is inserted into data channels intended for legitimate use.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized data access, data manipulation, and execution of arbitrary commands.
• Potential cascading effects include further system compromise, data breaches, and loss of data integrity.
• Business impact can involve financial loss, damage to reputation, and legal liabilities due to compromised data security.

• Prevention Guidelines:

• Specific code-level fixes include validating and sanitizing inputs to ensure that special characters are properly neutralized before being passed to downstream components.
• Security best practices involve using parameterized queries, prepared statements, and avoiding dynamic construction of queries or commands using user input.
• Recommended tools and frameworks include security libraries that provide input validation and output encoding, such as OWASP ESAPI, and static analysis tools to detect injection flaws during development.

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Technical Details

Likelihood of Exploit: High

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

const express = require('express');
const app = express();

// A vulnerable endpoint that directly uses user input in a command
app.get('/run', (req, res) => {
    const userCommand = req.query.command;
    // Dangerous: directly using user input in exec
    require('child_process').exec(`ls \${userCommand}`, (err, stdout, stderr) => {
        if (err) {
            return res.status(500).send('Error executing command');
        }
        res.send(stdout);
    });
});

app.listen(3000, () => console.log('Server running on port 3000'));

Explanation

In the vulnerable code example above, user input from req.query.command is directly inserted into a shell command executed by exec. This approach is dangerous because it allows for command injection, where an attacker could manipulate the input to execute arbitrary commands on the server.

How to fix Improper Neutralization of Special Elements in Output Used by a Downstream Component ('Injection')?

To fix command injection vulnerabilities, avoid constructing shell commands with user input. Instead, use safer alternatives like libraries or APIs that do not execute shell commands. If you must execute shell commands, validate and sanitize user input carefully, and use functions like execFile that accept command arguments separately, which reduces the risk of injection.

Fixed Code Example

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

// Secure endpoint using execFile to separate command and arguments
app.get('/run', (req, res) => {
    const userCommand = req.query.command;

    // Validate the user input to ensure it's safe
    if (!/^[\w-]+\$/.test(userCommand)) {
        return res.status(400).send('Invalid command');
    }

    // Use execFile for safer command execution
    execFile('ls', [userCommand], (err, stdout, stderr) => {
        if (err) {
            return res.status(500).send('Error executing command');
        }
        res.send(stdout);
    });
});

app.listen(3000, () => console.log('Server running on port 3000'));

Explanation

In the fixed code example, execFile is used instead of exec, which separates the command from its arguments, reducing the risk of injection. Additionally, a validation step is added to ensure that the userCommand only contains alphanumeric characters and hyphens, which prevents injection attacks by restricting the input to a safe subset of characters. This approach demonstrates a secure way to handle user input when interacting with the shell.