CWE-182: Collapse of Data into Unsafe Value

What is Collapse of Data into Unsafe Value?

• Overview: Collapse of Data into Unsafe Value (CWE-182) occurs when a software product processes or filters data in a manner that results in it being converted into a form that violates its intended security properties, potentially leading to security vulnerabilities.

• Exploitation Methods:

• Attackers can exploit this vulnerability by inputting data that gets transformed into a value that bypasses security checks.
• Common attack patterns include injecting specific characters or sequences that, after filtering or transformation, result in unintended or dangerous values.

• Security Impact:

• Direct consequences include bypassing authentication mechanisms, executing unauthorized actions, or accessing sensitive data.
• Potential cascading effects involve further system compromise, data breaches, or disrupting service availability.
• Business impact can be severe, leading to loss of customer trust, legal ramifications, and financial loss due to data breaches or service outages.

• Prevention Guidelines:

• Specific code-level fixes include validating input values both before and after any transformation or filtering process.
• Security best practices involve implementing strict input validation and sanitization, utilizing whitelists for acceptable input, and regularly reviewing and updating data processing logic.
• Recommended tools and frameworks include static analysis tools to detect potential data processing issues and employing security frameworks that provide robust input validation mechanisms.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

import re

def sanitize_input(input_string):
    # Vulnerable filtering process: Replaces non-word characters with a period,
    # which can collapse user input into an unsafe value. This could lead to security issues
    # such as XSS if the sanitized input is used in a web application without further validation.
    sanitized_string = re.sub(r'[^\w]', '.', input_string)
    return sanitized_string

user_input = "<script>alert('XSS')</script>"
print(sanitize_input(user_input))  # Outputs: .script.alert..XSS..script.

Explanation:

• The code uses a regular expression to replace any non-word character with a period. This can collapse user input into an unsafe value, potentially leading to security issues like XSS if the sanitized input is used in a web application without further validation and context-aware escaping.

How to fix Collapse of Data into Unsafe Value?

To fix this issue, it's crucial to avoid collapsing input data in a way that reduces its security properties. Instead of replacing all non-word characters, we should validate and explicitly allow only safe characters. This approach ensures that any potentially harmful input is rejected rather than transformed into a potentially dangerous form.

Best Practices:

1. Whitelist Validation: Define a set of allowed characters and reject anything outside the whitelist.
2. Input Encoding: Use proper encoding when displaying user input in different contexts (e.g., HTML encoding for web pages).
3. Contextual Escaping: Always escape output based on the context in which it will be used (e.g., HTML, JavaScript, URL).

Fixed Code Example

import re

def validate_input(input_string):
    # Improved validation: Only allows alphanumeric characters and spaces to ensure input safety.
    # If the input contains any invalid characters, an exception is raised to prevent unsafe data.
    if not re.fullmatch(r'[\w\s]*', input_string):
        raise ValueError("Input contains invalid characters.")
    return input_string

try:
    user_input = "<script>alert('XSS')</script>"
    print(validate_input(user_input))  # Raises ValueError
except ValueError as e:
    print(e)  # Outputs: Input contains invalid characters.

Explanation:

• Whitelist Validation: The code now validates the input by allowing only alphanumeric characters and spaces. This ensures that potentially harmful characters are not transformed into a dangerous form.
• Error Handling: By raising an exception when invalid input is detected, the application can handle such cases appropriately, avoiding potential security risks. This approach stops the processing of unsafe input early in the workflow.