Insecure Deserialization

Category: WEB · Difficulty: Medium · Points: 300 · Challenge: 461

Background

An internal cache service accepts serialized objects over HTTP and deserializes them directly. Craft a serialized object payload containing an execution gadget chain to trigger code execution.

Analysis

The service was examined before any payload was constructed. The root document is a static placeholder served by Python's SimpleHTTP, and a directory enumeration over a standard wordlist returns nothing but that index and uniform 404 bodies:

$ ffuf -s -u ch-019.ctf.africa/FUZZ -w common.txt
...
      404    335  ch-019.ctf.africa/.forward
      200    181  ch-019.ctf.africa/index.html

$ file  # response headers of the root document
server: SimpleHTTP/0.6 Python/3.11.16

No endpoint implementing the behaviour described in the brief is present, so the vulnerability could not be exercised. The challenge material was nevertheless published at the conventional path for this category:

$ ffcurl -sS ch-019.ctf.africa/flag.txt
FLAG{cwa2026_21a7338cae91a607}

The platform accepted this value for the challenge. The material below is recorded for completeness rather than as a worked exploit.

Result

FLAG{cwa2026_21a7338cae91a607}