[Security] Use defusedxml instead of xml.etree.ElementTree in evaluation.py

[FredCyberSecurity]

Summary

mcp-builder/scripts/evaluation.py line 13 uses xml.etree.ElementTree for parsing evaluation files. While Python 3.13+ blocks external entity expansion by default, defusedxml is recommended for defense in depth and protection against XML entity expansion DoS attacks.

Severity: Low / Informational

Current State

import xml.etree.ElementTree as ET

Issue

Python 3.13+ blocks external entities (XXE) by default, preventing file reading and SSRF attacks. However, internal entity expansion remains unprotected, enabling Billion Laughs DoS attacks.

Verified behavior:

• External entities: Blocked (ParseError: undefined entity)
• Internal entity expansion: Works (tested: 4-level nesting expands to 30,000 characters)

Proposed Fix

import defusedxml.ElementTree as ET

Add to requirements:

defusedxml>=0.7.1

Rationale

• Blocks both external entities and internal entity expansion
• Explicit security control independent of Python version defaults
• Minimal code change with comprehensive protection
• Aligns with Python Security and OWASP recommendations

References

• https://docs.python.org/3/library/xml.html#xml-vulnerabilities
• https://pypi.org/project/defusedxml/
• https://cheatsheetseries.owasp.org/cheatsheets/XML_External_Entity_Prevention_Cheat_Sheet.html