# Search for MEIPASS2 (older) or newer magic signatures = [b'MEIPASS2', b'MEIPASS'] for sig in signatures: idx = data.rfind(sig) if idx != -1: print(f"Found cookie at offset: idx") # Parse length (usually the next 4/8 bytes) cookie_len = struct.unpack('<I', data[idx+len(sig):idx+len(sig)+4])[0] print(f"Cookie length: cookie_len") return idx print("Cookie not found") return -1 find_cookie("myapp.exe")

import struct def find_cookie(filepath): with open(filepath, 'rb') as f: data = f.read()

A: PyInstaller’s built-in UPX compression is fine. But manually running UPX after building can sometimes corrupt the cookie. Avoid repacking.

(or MEIPASS2 in older versions). In a hex dump, you might see:

| Tool | Typical Command | Fails Due To | |------|----------------|---------------| | pyinstxtractor.py (original) | python pyinstxtractor.py myapp.exe | New PyInstaller version, corrupted archive | | pyi_archive_viewer (built into PyInstaller) | pyi-archive_viewer myapp.exe | Not a valid archive, or version mismatch | | pyinstxtractor-ng (modern fork) | python pyinstxtractor-ng.py myapp.exe | Malformed cookie, custom bootloader | | Unpacker scripts from GitHub | Varies | Hardcoded magic bytes | Before trying to fix the error, verify what you are actually dealing with. Step 1: Confirm It’s a PyInstaller Executable Use a hex editor (e.g., HxD, 010 Editor, or xxd on Linux) to inspect the last 100–200 bytes of the file.