3.0 KiB
Qubes-VM-hardening
Enhancing Qubes VM security and privacy
Pre-requisites:
Enabling authentication for sudo (see link below for Qubes doc).
vm-sudo-protect.service
- Protect /home script files
- Remove /rw scripts at VM start
Testing systemd version...
Install the two files vm-sudo-protect.sh and vm-sudo-protect.service into template then use systemctl to enable the service.
Activate by specifying as a Qubes service for each VM; There are two levels...
vm-sudo-protect- similar to the rc.local script. Protects scripts within /home and may be used with wide array of VMs including standalone, netVMs and Whonix.vm-sudo-protect-root- new feature which erases /rw/config, /rw/usrlocal and /rw/bind-dirs. Use with caution! This feature can also replace files on a global or per-VM basis... see script for details. Not recommended for standalone or VMs that rely on /rw root dirs such as netVMs or Whonix.
rc.local (old version)
Description:
Placed in /etc/rc.local (or equivalent) of a template VM, this makes the shell init files immutable so PATH and alias cannot be used to hijack commands like su and sudo, nor can impostor apps autostart whenever a VM starts. I combed the dash and bash docs -- as well as Gnome, KDE, Xfce and X11 docs -- to address all the user-writable startup files that apply. Feel free to comment or create an issue if you see an omission or other problem.
Although protecting init/autostart files should result in Qubes template-based VMs that boot 'cleanly' with much less chance of being affected by malware initially, it should be noted that subsequent running of some apps such as Firefox could conceivably allow malware to persist in a VM; this is because not only of the complexity of the formats handled by apps like Firefox and other browsers, but also because of settings contained in javascript code. Even if malware persists in a VM, it should be possible to run other apps and terminals without interference if sudo authentication is enabled and malware has not escalated to root via an exploit (admittedly, a big 'if').
All in all, this is one of the easy steps a Qubes user can take to make their VMs much less hospitable to intrusion and malware. Security can be further enhanced by enabling AppArmor or similar controls.
Note this sets the Linux immutable flag on files and directories, so intended modifications to the target files and dirs will require the extra step of disabling the flag using sudo chattr -i. Immutable is necessary because normal read-write permissions cannot prevent a normal user from removing other users' files (even root) from a dir they own; once removed, an init file like .bashrc can be re-created by the user process which opens the door to hijacking.