Patched code sample

import io

# The provided CVE is fictional. This code conceptually represents the logic
# used to fix a decompression bomb vulnerability like the one described.
# The actual fix is internal to the py7zr library, but this demonstrates the
# core principle: tracking cumulative size and enforcing a limit.

def secure_decompress_worker(archive_members, max_total_size):
    """
    A simplified worker that simulates secure decompression by checking file sizes
    against a maximum limit before 'extracting' them. A vulnerable version would
    lack the size check inside this loop.
    """
    total_decompressed_size = 0
    print(f"Starting decompression with a size limit of {max_total_size} bytes.")

    for member in archive_members:
        member_name = member['name']
        member_size = member['uncompressed_size']

        # --- THE FIX ---
        # This security check was missing in the vulnerable version. It ensures
        # the next file to be extracted will not exceed the total size limit.
        if total_decompressed_size + member_size > max_total_size:
            raise ValueError(
                f"Extraction aborted: Archive would exceed the max size limit. "
                f"'{member_name}' of size {member_size} would cause the total "
                f"to exceed the limit of {max_total_size} bytes."
            )
        # --- END OF FIX ---

        # Simulate the decompression of a single file.
        print(f"Decompressing '{member_name}' ({member_size} bytes)...")
        total_decompressed_size += member_size

    print(f"\nDecompression successful. Total size: {total_decompressed_size} bytes.")


if __name__ == '__main__':
    # A mock archive representing a "decompression bomb".
    # e.g., A small .7z file that expands to over 100 MB.
    bomb_archive_members = [
        {"name": "file1.dat", "uncompressed_size": 60 * 1024 * 1024},  # 60 MB
        {"name": "file2.dat", "uncompressed_size": 50 * 1024 * 1024},  # 50 MB
    ]

    # A security limit to prevent resource exhaustion (disk or memory).
    MAX_DECOMPRESSION_BYTES = 100 * 1024 * 1024  # 100 MB

    try:
        # A call to the fixed version of the library would have this check internally.
        secure_decompress_worker(bomb_archive_members, MAX_DECOMPRESSION_BYTES)
    except ValueError as e:
        print("\n---")
        print("SUCCESS: Decompression bomb detected and prevented by the fix.")
        print(f"Error message: {e}")
        print("---")