CWE-163: Improper Neutralization of Multiple Trailing Special Elements

What is Improper Neutralization of Multiple Trailing Special Elements?

• Overview: This vulnerability occurs when software does not properly handle or neutralize multiple special characters at the end of input data. If these characters are not managed correctly, they can be misinterpreted by the system, leading to unexpected behaviors or security flaws.

• Exploitation Methods:

• Attackers can exploit this vulnerability by crafting inputs with multiple trailing special characters to disrupt normal processing or execute malicious actions.
• Common attack patterns include injecting special characters to manipulate command execution, data parsing, or control flow on downstream components.

• Security Impact:

• Direct consequences include unauthorized actions being performed, data corruption, or unexpected system behavior.
• Potential cascading effects could involve triggering vulnerabilities in other components of the system or spreading the attack to connected systems.
• Business impact might include data breaches, service disruptions, loss of customer trust, and financial losses due to system downtime or legal liabilities.

• Prevention Guidelines:

• Ensure proper validation and sanitization of all input data, specifically focusing on neutralizing or escaping trailing special characters.
• Implement security best practices such as input encoding, using parameterized queries, and employing rigorous input validation.
• Utilize recommended tools and frameworks that provide built-in functions for secure input handling, such as web application firewalls (WAFs) and security libraries that automatically neutralize special characters.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

function executeCommand(userInput) {
    // Directly using user input in eval() is highly dangerous
    // This code does not neutralize multiple trailing special elements
    eval("console.log('" + userInput + "')");  // This allows code injection
}

let userInput = "hello'; console.log('malicious code'); //";
executeCommand(userInput);

Explanation:

• Use of eval(): The eval() function executes code represented as a string. When user input is passed directly to eval(), it poses a significant security risk.
• Vulnerability Demonstration: The input "hello'; console.log('malicious code'); //" illustrates how an attacker can inject additional commands, leading to unintended code execution.

How to fix Improper Neutralization of Multiple Trailing Special Elements?

To mitigate this vulnerability:

• Avoid eval(): Refrain from using eval() with user input. Consider safer alternatives such as JSON handling or templating libraries.
• Sanitize Input: Escape special characters to prevent them from being interpreted as code.
• Validate Input: Ensure that input adheres to expected patterns and formats.

Fixed Code Example

function safeExecuteCommand(userInput) {
    // Use JSON.stringify to safely handle user input, ensuring special characters are escaped
    console.log(JSON.stringify(userInput));  // Outputs user input safely
}

let userInput = "hello'; console.log('malicious code'); //";
safeExecuteCommand(userInput);

Key Changes:

• Avoid eval(): The fixed example uses JSON.stringify() to handle user input safely. This method escapes special characters, preventing code execution.
• Secure Output: By converting user input to a JSON string, we ensure that it is treated as a plain string, not executable code.
• Enhanced Security: This approach mitigates the risk of code injection by avoiding the execution of user-supplied strings as code.