CWE-152: Improper Neutralization of Macro Symbols

What is Improper Neutralization of Macro Symbols?

• Overview: Improper Neutralization of Macro Symbols occurs when software receives input containing special elements that could be interpreted as macro symbols, but it fails to properly neutralize or sanitize these elements before passing them to another component, potentially leading to unintended execution or behavior.

• Exploitation Methods:

• Attackers can exploit this vulnerability by injecting malicious macro symbols into input fields that are processed by the software.
• Common attack patterns include exploiting macro expansion features in document processing or scripting environments, where the input is interpreted as executable code.

• Security Impact:

• Direct consequences of successful exploitation may include unauthorized execution of code or commands, leading to data breaches or system compromise.
• Potential cascading effects involve further exploitation of the system, such as privilege escalation or spreading malware.
• Business impact could include data loss, reputational damage, regulatory fines, and operational disruptions.

• Prevention Guidelines:

• Specific code-level fixes involve implementing strict input validation and output encoding to ensure that macro symbols are properly neutralized.
• Security best practices include adopting a principle of least privilege and maintaining up-to-date libraries and dependencies.
• Recommended tools and frameworks involve using static analysis tools to detect vulnerabilities and employing secure coding frameworks that provide built-in protection against macro symbol issues.

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Technical Details

Likelihood of Exploit: Not specified

Affected Languages: Not Language-Specific

Affected Technologies: Not specified

Vulnerable Code Example

Python Example

import jinja2

def render_template(template_string, context):
    # Vulnerable code: the template string is passed directly to Jinja2 without neutralization
    template = jinja2.Template(template_string)
    return template.render(context)

# Example usage
template_string = "{{ data }}"
context = {"data": "User input: {{ dangerous_function() }}"}

# This could potentially execute dangerous_function() if not properly neutralized
result = render_template(template_string, context)
print(result)

Explanation of Vulnerability:

• The code uses the Jinja2 templating engine to render a template string with a context dictionary.
• The template_string and context come from user input, which could include macro symbols.
• If the context contains macro symbols or functions like {{ dangerous_function() }}, it could lead to unintended execution of code.
• This vulnerability arises because Jinja2 evaluates expressions within {{ }}, allowing for potential code execution if not properly handled.

How to fix Improper Neutralization of Macro Symbols?

Fixed Code Example

Python Example

import jinja2
from jinja2 import Environment, select_autoescape

def render_template(template_string, context):
    # Fixed: Use Jinja2 environment with autoescaping enabled for HTML/XML
    env = Environment(autoescape=select_autoescape(['html', 'xml']))  # {9}
    template = env.from_string(template_string)
    return template.render(context)  # {11}

# Example usage
template_string = "{{ data }}"
context = {"data": "User input: {{ dangerous_function() }}"}

# Now the dangerous_function() will be interpreted as plain text and not executed
result = render_template(template_string, context)
print(result)

Explanation of the Fix:

• Autoescaping: The Jinja2 environment is configured with autoescape enabled for HTML/XML content, which neutralizes any macro symbols by treating them as plain text.
• Safe Template Environment: By using Environment with select_autoescape, we ensure that any expressions within {{ }} are automatically escaped, preventing unintended code execution.
• This approach maintains the integrity of the template rendering process while safeguarding against macro symbol injection, effectively mitigating the risk of code execution vulnerabilities.