CSAW 2024 ZipZipZipZi........

ZipZipZipZi…

Brighten up at last with the flag

We are given a singular zip file. When unzipping with unzip challenge.zip, we are given chunk1.zip and chunk0.txt. Looking at chunk0.txt, it looks like base64. So, we can assume we need to recursively unzip, grab all the chunks, and convert our base64 into a file.

import subprocess
import base64
 
nextZip = "challenge.zip"
chunks = []
 
try:
    while True:
        if "zip" not in nextZip: break
        unzip = f"unzip {nextZip}"
        rm = f"rm {nextZip}"
        output = subprocess.check_output(unzip, shell=True).decode()
        if "extracting" in output:
            print(output)
            nextZip = output.split()[-1]
            print(f"Extracted {nextZip}")
            chunks.append(nextZip.replace(".zip", ".txt"))
            subprocess.check_output(rm, shell=True)
        else:
            print("Finished")
            break
except KeyboardInterrupt:
    print("ok we done")
    pass
 
base64png = ""
for chunk in chunks[:-1]:
    with open(chunk, "r") as f:
        base64png += f.read().strip()
with open("flag.png", "wb") as f:
    f.write(base64.b64decode(base64png + "=="))