CWE-167: Improper Handling of Additional Special Element

What is Improper Handling of Additional Special Element?

• Overview: Improper Handling of Additional Special Element occurs when a software product receives input from an upstream source and fails to correctly handle unexpected or additional special elements in that input, leading to potential security vulnerabilities.

• Exploitation Methods:

• Attackers can exploit this vulnerability by injecting unexpected special elements into the input stream, which the system may mishandle.
• Common attack patterns include input manipulation through crafted payloads designed to bypass input validation or exploit parsing errors.

• Security Impact:

• Direct consequences of successful exploitation can include unauthorized access, data corruption, or denial of service.
• Potential cascading effects might involve the compromise of interconnected systems or exposure of sensitive data.
• Business impact could include financial loss, reputational damage, and legal liability due to data breaches or service disruptions.

• Prevention Guidelines:

• Specific code-level fixes include implementing robust input validation and sanitation routines to handle all input variations safely.
• Security best practices involve adopting a defensive programming approach, thoroughly testing input handling, and employing whitelisting strategies for allowable input.
• Recommended tools and frameworks include those that provide input validation and sanitization libraries, such as OWASP ESAPI, and static analysis tools to detect improper input handling.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

// inputHandler.js {14-18}
function parseInputData(inputStr) {
    try {
        // Vulnerable line: The input string is parsed without checking for unexpected additional elements
        let inputData = JSON.parse(inputStr);
        // Assuming inputData is an object with a 'username' field
        let username = inputData.username;
        return `Welcome, \${username}!`;
    } catch (e) {
        return "Invalid input data";
    }
}

// Example of problematic input
console.log(parseInputData('{"username": {"first": "Alice", "last": "Smith"}}'));

Explanation

In the vulnerable code example, the parseInputData function directly parses the input string into a JavaScript object using JSON.parse. It assumes that the parsed object will have a simple structure with a username field as a string. However, the input could contain unexpected nested structures, which could lead to incorrect behavior or security issues if the username field is not a string.

How to fix Improper Handling of Additional Special Element?

To address this vulnerability, strict validation of the JSON structure is necessary. Implement a function that verifies if the parsed data matches the expected structure before proceeding. This involves checking the types and presence of required fields and enforcing these rules using a JSON schema library if available, or manually if not. This ensures that any unexpected nested structures or additional elements do not lead to incorrect behavior.

Fixed Code Example

// inputHandler.js {14-23}
function parseInputData(inputStr) {
    try {
        let inputData = JSON.parse(inputStr);
        // Validate the structure of inputData
        if (typeof inputData === 'object' && typeof inputData.username === 'string') {
            let username = inputData.username;
            return `Welcome, \${username}!`;
        } else {
            throw new Error("Invalid structure");
        }
    } catch (e) {
        console.error(`Error: \${e.message}`);
        return "Invalid input data";
    }
}

// Example of properly handled input
console.log(parseInputData('{"username": "Alice"}'));

Explanation

In the fixed code example, before using the username field, the code checks that inputData is an object and that inputData.username is a string. This prevents unexpected nested objects from being used as a username, which could otherwise lead to security issues or incorrect application behavior. Additionally, error handling is improved by logging the error message to the console, aiding in debugging.