CWE-156: Improper Neutralization of Whitespace

What is Improper Neutralization of Whitespace?

• Overview: Improper Neutralization of Whitespace (CWE-156) occurs when a software product receives input and fails to correctly handle special whitespace elements such as spaces or tabs, potentially leading to unintended behavior when input is passed to another component.

• Exploitation Methods:

• Attackers can exploit this vulnerability by embedding malicious whitespace in input to manipulate how the input is processed by different systems or components.
• Common attack patterns include injecting tabs or spaces to alter command parsing or circumvent security checks.

• Security Impact:

• Direct consequences of successful exploitation include unauthorized access, data leakage, or execution of unintended commands.
• Potential cascading effects involve further exploitation of system vulnerabilities or bypassing authentication and authorization mechanisms.
• Business impact may include loss of data integrity, unauthorized access to sensitive information, and reputational damage.

• Prevention Guidelines:

• Specific code-level fixes include thorough input validation and sanitization processes that explicitly handle and neutralize all forms of whitespace.
• Security best practices involve implementing rigorous input validation checks and defining clear parsing rules for input data.
• Recommended tools and frameworks include static analysis tools for detecting improper input handling and using libraries that offer robust input validation functions.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

def process_input(user_input):
    # This function processes user input and logs it
    # Improper neutralization of whitespace: newline and tab characters are not handled
    log_message = f"User Input Received: {user_input}"
    print(log_message)  # Vulnerability: user_input may contain malicious whitespace characters

# Example usage
user_input = "Hello\nWorld\t!"
process_input(user_input)

Explanation

In the above code, the process_input function directly logs user input without sanitizing it. This is a vulnerability because special whitespace characters like newlines (\n) and tabs (\t) can be used by an attacker to manipulate log files. For instance, an attacker could use newlines to insert additional log entries, potentially hiding malicious activities or injecting misleading information into the logs.

How to fix Improper Neutralization of Whitespace?

To fix this vulnerability, sanitize the user input by neutralizing potentially harmful whitespace characters before using it in logs or other sensitive downstream processes. This can be done by replacing or encoding these characters into a safe format that cannot be misinterpreted as control characters.

Fixed Code Example

import re

def process_input(user_input):
    # Sanitize input by replacing newline and tab characters with safe placeholders
    sanitized_input = re.sub(r'[\n\t]', '_', user_input)  # Replace newline and tab with underscores
    log_message = f"User Input Received: {sanitized_input}"
    print(log_message)  # Safe: potentially harmful whitespace is neutralized

# Example usage
user_input = "Hello\nWorld\t!"
process_input(user_input)

Explanation

In the fixed code, we use a regular expression to replace newline (\n) and tab (\t) characters with underscores (_) before logging the user input. This ensures that the input cannot be misinterpreted as control characters when logged, thereby preventing log injection attacks. By neutralizing these characters, we maintain the integrity of the log data and protect against potential log manipulation.