Vulnerable code sample

import fnmatch
import unicodedata

# This is a simplified representation of the setuptools FileList logic 
# before the Unicode normalization fix.

def find_files_vulnerable(all_files, exclude_patterns):
    """
    Filters a list of files based on exclusion patterns, without
    performing Unicode normalization, mimicking the vulnerable behavior.
    """
    included_files = []
    for filename in all_files:
        is_excluded = False
        for pattern in exclude_patterns:
            # The core of the vulnerability: fnmatch compares raw strings.
            # It does not account for Unicode canonical equivalence.
            if fnmatch.fnmatch(filename, pattern):
                is_excluded = True
                break
        if not is_excluded:
            included_files.append(filename)
    return included_files

# --- Demonstration ---

# 1. A developer wants to exclude a file with a special character.
# They write the name in NFC (Normalized Form Composed), which is standard.
# 'í' is a single character \u00ed.
developer_exclusion_rule = "secret_fíle.txt" 

# 2. An attacker creates a file with the same visual name, but in NFD
# (Normalized Form Decomposed). On macOS, this is a valid filename.
# 'í' is represented as 'i' followed by a combining accent character ´ (\u0301).
attacker_filename_nfd = "secret_fi\u0301le.txt"

# Verify the strings are different byte-for-byte
# assert developer_exclusion_rule != attacker_filename_nfd
# But they are canonically equivalent
# assert unicodedata.normalize('NFC', attacker_filename_nfd) == developer_exclusion_rule

# 3. Simulate the list of files found on disk.
disk_files = ["setup.py", "my_module.py", attacker_filename_nfd]

# 4. Simulate the exclusion rules from a MANIFEST.in file.
manifest_exclusions = [developer_exclusion_rule]

# 5. Run the vulnerable logic.
packaged_files = find_files_vulnerable(disk_files, manifest_exclusions)

# The output would show that the attacker's file bypassed the exclusion.
# print(f"Files that would be packaged: {packaged_files}")
# Expected vulnerable result: ['setup.py', 'my_module.py', 'secret_fi\u0301le.txt']