CWE-253: Incorrect Check of Function Return Value

What is Incorrect Check of Function Return Value?

• Overview: Incorrect Check of Function Return Value (CWE-253) occurs when a program fails to properly verify the return value of a function, potentially missing errors or exceptions that need to be handled.

• Exploitation Methods:

• Attackers can exploit this vulnerability by triggering code paths where error handling is skipped, leading to undefined behavior.
• Common attack patterns include feeding unexpected input to functions, causing them to fail silently without triggering necessary error handling.

• Security Impact:

• Direct consequences of successful exploitation include application crashes, data corruption, or unauthorized actions.
• Potential cascading effects include further exploitation of subsequent vulnerabilities due to lack of error handling.
• Business impact can include loss of data integrity, system downtime, and potential breaches of sensitive information.

• Prevention Guidelines:

• Specific code-level fixes include checking and handling all return values from functions, especially those that indicate errors.
• Security best practices involve thorough testing and validation of error handling paths and using assertions or exceptions where appropriate.
• Recommended tools and frameworks include static analysis tools that can detect missing error checks and coding standards that enforce return value handling.

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Technical Details

Likelihood of Exploit: Low

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

import os

def read_file(file_path):
    # Attempt to open the file and read its contents
    f = open(file_path, 'r')  # This can raise an exception if the file cannot be opened
    content = f.read()
    f.close()
    return content

# Usage
print(read_file("/path/to/file.txt"))

Explanation:

• The function open(file_path, 'r') can fail for several reasons, such as if the file does not exist, the path is incorrect, or the program lacks the necessary permissions. In this example, the code does not check for these conditions and does not handle exceptions. If an error occurs, it will raise an unhandled exception, potentially crashing the program.

How to fix Incorrect Check of Function Return Value?

To address this issue, use a try-except block to handle exceptions. This approach allows the program to manage errors gracefully, providing informative feedback to the user and preventing crashes. Additionally, using a context manager (with statement) ensures that resources are managed correctly, even if an error occurs.

Fixed Code Example

import os

def read_file(file_path):
    # Use a try-except block to handle potential exceptions
    try:
        with open(file_path, 'r') as f:  # Automatically manages file closing
            content = f.read()
        return content
    except FileNotFoundError:  # Handle the case where the file does not exist
        print(f"Error: The file {file_path} was not found.")
    except PermissionError:  # Handle the case where the program lacks read permissions
        print(f"Error: Permission denied when trying to read {file_path}.")
    except IOError as e:  # Handle other I/O related errors
        print(f"Error: An IOError occurred. {str(e)}")
    return None  # Return None to indicate failure

# Usage
print(read_file("/path/to/file.txt"))

Explanation:

• The with open(file_path, 'r') as f: statement ensures that the file is properly closed after its contents are read, even if an error occurs during the read operation.
• The try-except block captures specific exceptions like FileNotFoundError, PermissionError, and IOError, providing the user with clear and informative error messages. This prevents the program from crashing unexpectedly.
• By returning None when an error is encountered, the function maintains consistent return behavior, allowing the caller to handle the error appropriately.