CWE-115: Misinterpretation of Input

What is Misinterpretation of Input?

• Overview: Misinterpretation of Input (CWE-115) occurs when software incorrectly processes input data, leading to unintended behavior. This can happen when input from users, other systems, or attackers is misunderstood by the program, particularly in a way that impacts security.

• Exploitation Methods:

• Attackers can exploit this by crafting input that the software misinterprets, triggering incorrect operations.
• Common attack patterns include sending data that looks valid but is interpreted differently by various components or exploiting discrepancies in how data is processed.

• Security Impact:

• Direct consequences include unauthorized access, data leakage, or execution of unintended commands.
• Potential cascading effects involve further exploitation of the system's weaknesses, leading to broader security breaches.
• Business impact can be significant, including loss of customer trust, legal repercussions, and financial losses due to data breaches.

• Prevention Guidelines:

• Specific code-level fixes include validating and sanitizing all inputs rigorously, ensuring they conform to expected formats and types.
• Security best practices involve implementing input validation libraries, using type-safe methods, and avoiding assumptions about input data.
• Recommended tools and frameworks include static analysis tools to detect improper input handling and frameworks that provide secure input processing routines.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

// Function to process user input from a web form
function processUserInput(input) {
    // Vulnerable: Misinterpreting input as a number without validation
    let userId = parseInt(input); // Attempts to convert input to an integer
    console.log("Processing user ID: " + userId);
    
    // Further processing with userId...
}

// Simulated user input
processUserInput("123abc"); // Misinterpreted as 123 instead of invalid input

How to fix Misinterpretation of Input?

The core issue in the vulnerable code is that the parseInt function attempts to convert the input into an integer, stopping at the first non-numeric character. This can lead to misinterpretation of the input, where an attacker might manipulate inputs to cause unintended behavior or errors in the application.

To fix this vulnerability, we need to validate the input string to ensure it only contains numeric characters before performing any conversion. This can be done using regular expressions to match against a pattern that only allows numeric strings.

Fixed Code Example

// Function to process user input from a web form with validation
function processUserInput(input) {
    // Fixed: Validate input with a regular expression to ensure it's numeric
    if (/^\d+\$/.test(input)) { // Check if input is a numeric string
        let userId = parseInt(input); // Safe to convert to an integer
        console.log("Processing user ID: " + userId);
        
        // Further processing with userId...
    } else {
        console.error("Invalid input: Input must be a numeric string");
    }
}

// Simulated user input
processUserInput("123abc"); // Properly identified as invalid input
processUserInput("123");    // Valid input, processed correctly

In the fixed code, we use the regular expression /^\d+\$/ to ensure that the input is a numeric string before converting it to an integer. This prevents any misinterpretation by ensuring the input meets the expected format, thus mitigating the security risk associated with misinterpreted input. The regular expression checks that the entire input consists only of digits, which is crucial for maintaining the correct data integrity and preventing potential security issues.