CWE-1285: Improper Validation of Specified Index, Position, or Offset in Input

What is Improper Validation of Specified Index, Position, or Offset in Input?

• Overview: Improper Validation of Specified Index, Position, or Offset in Input refers to a situation where software does not properly check if an index, position, or offset used to access resources like buffers or files is valid, which can lead to unauthorized access or manipulation of data.

• Exploitation Methods:

• Attackers can provide specially crafted input that specifies an out-of-bounds index or offset to access or manipulate data outside the intended boundaries.
• Common attack patterns include buffer overflows or accessing unintended memory areas, potentially leading to data corruption or unauthorized data access.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access to sensitive data, application crashes, and data corruption.
• Potential cascading effects involve further exploitation through arbitrary code execution or denial of service.
• Business impact can include data breaches, loss of customer trust, and legal liabilities.

• Prevention Guidelines:

• Specific code-level fixes include validating inputs by checking if indices or offsets are within the expected range before using them.
• Security best practices involve implementing input validation, using safer functions that handle bounds checking, and employing exception handling to manage errors.
• Recommended tools and frameworks include static analysis tools to detect unsafe code patterns and using languages or libraries that provide built-in bounds checking.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

function processFile(data, index) {
    // Directly using the index without validation
    let result = data.substring(index);
    return result;
}

// Example usage
let content = processFile("Hello, World!", 15);

Explanation:

• Vulnerability: The processFile function uses an index to access a substring of data. Without validating the index, if it's out of bounds (e.g., greater than the string length or negative), it can lead to unexpected behavior or runtime errors.

How to fix Improper Validation of Specified Index, Position, or Offset in Input?

To fix this vulnerability:

1. Validate the Index: Ensure the index is within the valid range of the string length.
2. Handle Edge Cases: Consider cases where the index is exactly the length of the string or zero.
3. Graceful Error Handling: Provide meaningful feedback or default behavior when invalid input is detected.

Fixed Code Example

function processFile(data, index) {
    // Validate the index to ensure it's within bounds
    if (index < 0 || index > data.length) {
        throw new Error("Index is out of bounds");
    }
    // Safely extract the substring starting from the validated index
    let result = data.substring(index);
    return result;
}

// Example usage with error handling
try {
    let content = processFile("Hello, World!", 15);
} catch (error) {
    console.log(`Error: \${error.message}`);
}

Explanation:

• Index Validation: The code now checks if the index is within the valid range of the string length, preventing out-of-bounds access.
• Error Handling: An error is thrown if the index is invalid, which allows the calling code to handle this scenario gracefully.
• Graceful Degradation: The code provides meaningful feedback when invalid input is detected, improving the robustness and reliability of the application.