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# System-wide Protection
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Experimental system-wide XML protection by monkey-patching all standard library XML modules with defused alternatives. This provides comprehensive protection across an entire Python application without requiring individual module imports to be changed.
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## Capabilities
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### Global Monkey Patching
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System-wide monkey patching function that replaces all standard library XML modules with defused alternatives.
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```python { .api }
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def defuse_stdlib():
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"""
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Monkey patch and defuse all standard library XML packages.
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Replaces the following standard library modules with defused alternatives:
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- xml.etree.ElementTree -> defusedxml.ElementTree
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- xml.etree.cElementTree -> defusedxml.cElementTree
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- xml.sax -> defusedxml.sax
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- xml.dom.minidom -> defusedxml.minidom
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- xml.dom.pulldom -> defusedxml.pulldom
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- xml.dom.expatbuilder -> defusedxml.expatbuilder
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- xml.sax.expatreader -> defusedxml.expatreader
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- xmlrpc.client/xmlrpclib -> defusedxml.xmlrpc (via monkey_patch)
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Returns:
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dict: Mapping of defused modules to original stdlib modules
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Warning:
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This is an EXPERIMENTAL feature. The monkey patch is global
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and affects all XML processing in the current Python process.
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Use with caution in production environments.
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"""
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```
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**Usage Examples:**
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```python
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import defusedxml
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# Apply global XML security patches
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defused_modules = defusedxml.defuse_stdlib()
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print(f"Defused {len(defused_modules)} XML modules")
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# Now all XML processing uses defused implementations automatically
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import xml.etree.ElementTree as ET # Actually uses defusedxml.ElementTree
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import xml.sax as sax # Actually uses defusedxml.sax
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import xml.dom.minidom as minidom # Actually uses defusedxml.minidom
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# Parse XML normally - it's automatically secured
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root = ET.fromstring('<root><item>value</item></root>')
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print(f"Root element: {root.tag}")
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# SAX parsing is also automatically secured
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from xml.sax.handler import ContentHandler
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class MyHandler(ContentHandler):
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def startElement(self, name, attrs):
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print(f"Element: {name}")
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handler = MyHandler()
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sax.parseString('<root><item>test</item></root>', handler)
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```
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## Implementation Details
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The `defuse_stdlib()` function works by:
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1. **Module Import**: Importing all defusedxml modules to ensure they're available
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2. **Standard Library Import**: Importing corresponding standard library modules
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3. **Attribute Replacement**: Replacing public attributes in standard library modules with defused equivalents
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4. **XML-RPC Patching**: Applying special XML-RPC monkey patches via `xmlrpc.monkey_patch()`
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5. **Return Mapping**: Returning a dictionary mapping defused modules to original modules
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## Security Considerations
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### Advantages
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- **Comprehensive Protection**: All XML processing in the application is automatically secured
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- **Zero Code Changes**: Existing code continues to work without modification
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- **Consistent Security**: No risk of accidentally using unsecured XML processing
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- **Third-party Library Protection**: Libraries that use standard XML modules are automatically protected
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### Disadvantages and Risks
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- **Global Side Effects**: Affects all XML processing system-wide, potentially breaking compatibility
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- **Experimental Status**: Not recommended for production use without thorough testing
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- **Performance Impact**: May introduce slight performance overhead
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- **Debugging Complexity**: Stack traces may be confusing due to module replacement
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- **Library Compatibility**: Some libraries may break if they rely on specific standard library behavior
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## Common Usage Patterns
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### Application Initialization
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```python
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import defusedxml
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import logging
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def initialize_security():
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"""Initialize application-wide XML security."""
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try:
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defused_modules = defusedxml.defuse_stdlib()
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logging.info(f"XML security initialized: defused {len(defused_modules)} modules")
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# Log which modules were defused
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for defused_mod, stdlib_mod in defused_modules.items():
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if stdlib_mod:
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logging.debug(f"Defused: {defused_mod.__name__} -> {stdlib_mod.__name__}")
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else:
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logging.debug(f"Patched: {defused_mod.__name__}")
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return True
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except Exception as e:
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logging.error(f"Failed to initialize XML security: {e}")
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return False
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# Call during application startup
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if __name__ == "__main__":
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if initialize_security():
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print("Application starting with XML security enabled")
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main()
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else:
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print("Warning: XML security initialization failed")
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main()
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```
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### Conditional Security Application
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```python
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import os
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import defusedxml
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def apply_xml_security():
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"""Apply XML security based on configuration."""
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# Check environment variable
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enable_security = os.getenv('ENABLE_XML_SECURITY', 'true').lower() == 'true'
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if enable_security:
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print("Applying system-wide XML security patches...")
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defused_modules = defusedxml.defuse_stdlib()
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print(f"Successfully defused {len(defused_modules)} XML modules")
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else:
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print("XML security patches disabled by configuration")
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# Apply security conditionally
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apply_xml_security()
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# Rest of application continues normally
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import xml.etree.ElementTree as ET
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# This uses defused implementation if security was applied
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```
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### Testing with Security Patches
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```python
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import unittest
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import defusedxml
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class TestWithXMLSecurity(unittest.TestCase):
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"""Test case that applies XML security patches."""
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@classmethod
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def setUpClass(cls):
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"""Apply XML security patches before running tests."""
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cls.defused_modules = defusedxml.defuse_stdlib()
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print(f"Test suite using defused XML modules: {len(cls.defused_modules)}")
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def test_xml_parsing(self):
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"""Test that XML parsing works with security patches."""
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import xml.etree.ElementTree as ET
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# This should work normally
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xml_content = '<root><item>test</item></root>'
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root = ET.fromstring(xml_content)
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self.assertEqual(root.tag, 'root')
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self.assertEqual(root[0].text, 'test')
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def test_malicious_xml_blocked(self):
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"""Test that malicious XML is blocked."""
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import xml.etree.ElementTree as ET
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import defusedxml
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# XML with external entity (should be blocked)
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malicious_xml = '''<?xml version="1.0"?>
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<!DOCTYPE root [
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<!ENTITY external SYSTEM "file:///etc/passwd">
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]>
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<root>&external;</root>'''
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with self.assertRaises(defusedxml.ExternalReferenceForbidden):
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ET.fromstring(malicious_xml)
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if __name__ == '__main__':
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unittest.main()
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```
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### Library Integration
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```python
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import defusedxml
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class SecureXMLProcessor:
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"""XML processor that ensures security is applied."""
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def __init__(self, auto_defuse=True):
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"""Initialize processor with optional auto-defusing."""
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self.auto_defuse = auto_defuse
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self.defused_modules = None
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if auto_defuse:
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self.enable_security()
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def enable_security(self):
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"""Enable XML security patches."""
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if not self.defused_modules:
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self.defused_modules = defusedxml.defuse_stdlib()
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print(f"XML security enabled: {len(self.defused_modules)} modules defused")
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def process_xml(self, xml_content):
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"""Process XML content with security enabled."""
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import xml.etree.ElementTree as ET
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try:
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root = ET.fromstring(xml_content)
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return self._extract_data(root)
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except Exception as e:
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print(f"XML processing failed: {e}")
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return None
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def _extract_data(self, root):
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"""Extract data from XML root element."""
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data = {'tag': root.tag, 'attributes': dict(root.attrib)}
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# Extract child elements
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children = []
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for child in root:
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children.append({
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'tag': child.tag,
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'text': child.text,
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'attributes': dict(child.attrib)
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})
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data['children'] = children
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return data
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# Usage
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processor = SecureXMLProcessor()
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result = processor.process_xml('<root><item id="1">value</item></root>')
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print(result)
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```
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### Monitoring and Logging
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```python
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import defusedxml
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import logging
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import sys
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class XMLSecurityMonitor:
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"""Monitor XML security status and violations."""
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def __init__(self):
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self.security_enabled = False
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self.defused_modules = None
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self.violation_count = 0
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# Set up logging
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logging.basicConfig(level=logging.INFO)
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self.logger = logging.getLogger(__name__)
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def enable_security(self):
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"""Enable XML security with monitoring."""
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try:
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self.defused_modules = defusedxml.defuse_stdlib()
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self.security_enabled = True
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self.logger.info(f"XML security enabled: {len(self.defused_modules)} modules defused")
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# Install exception handler to monitor violations
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self._install_violation_handler()
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except Exception as e:
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self.logger.error(f"Failed to enable XML security: {e}")
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self.security_enabled = False
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def _install_violation_handler(self):
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"""Install handler to monitor security violations."""
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original_excepthook = sys.excepthook
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monitor = self
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def security_aware_excepthook(exctype, value, traceback):
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if issubclass(exctype, defusedxml.DefusedXmlException):
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monitor.violation_count += 1
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monitor.logger.warning(f"XML security violation #{monitor.violation_count}: {value}")
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original_excepthook(exctype, value, traceback)
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sys.excepthook = security_aware_excepthook
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def get_status(self):
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"""Get current security status."""
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return {
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'security_enabled': self.security_enabled,
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'defused_modules': len(self.defused_modules) if self.defused_modules else 0,
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'violation_count': self.violation_count
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}
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# Usage
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monitor = XMLSecurityMonitor()
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monitor.enable_security()
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# Later in application
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status = monitor.get_status()
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print(f"XML Security Status: {status}")
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```
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## Best Practices
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### Production Considerations
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1. **Thorough Testing**: Test all XML processing functionality after applying patches
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2. **Staged Rollout**: Apply in development/staging environments first
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3. **Monitoring**: Implement monitoring for XML security violations
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4. **Fallback Plan**: Have a plan to disable patches if compatibility issues arise
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5. **Documentation**: Document the use of system-wide patches for maintenance teams
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### Alternative Approaches
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Instead of system-wide patching, consider:
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```python
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# Selective module replacement
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import defusedxml.ElementTree as ET # Explicitly use defused version
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import defusedxml.sax as sax # Explicitly use defused version
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# Library-specific protection
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import defusedxml.xmlrpc as xmlrpc_defused
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xmlrpc_defused.monkey_patch() # Only patch XML-RPC
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# Application-level wrappers
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def safe_parse_xml(xml_content):
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import defusedxml.ElementTree as ET
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return ET.fromstring(xml_content)
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```
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## Migration Considerations
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When migrating from individual defused imports to system-wide patching:
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```python
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# Before: Individual imports
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import defusedxml.ElementTree as ET
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import defusedxml.sax as sax
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root = ET.fromstring(xml_content)
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# After: System-wide patching
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import defusedxml
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defusedxml.defuse_stdlib()
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import xml.etree.ElementTree as ET # Now automatically defused
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import xml.sax as sax # Now automatically defused
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root = ET.fromstring(xml_content) # Same API, but secured
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```
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The main advantage is that existing code and third-party libraries automatically benefit from security protections without modification.