Qubes-VM-hardening

README under construction

Fend off malware at VM startup: Lock-down and remove scripts in /rw private storage that affect the execution environment.

vm-boot-protect.service

• Protect /home (user) executable files as immutable
• Deactivate /rw (root) executables
• Whitelisting for specifying persistent files
• SHA256 checksumming guards against unwanted changes
• Deploy custom defaut files
• Runs at VM start before /rw mounts

Installing

1. In a template VM, install the two service files

   cd Qubes-VM-hardening
   sudo sh ./install
   

2. Activate by specifying one of the following Qubes services for your VM(s)...

   • vm-boot-protect - Protects executables/scripts within /home/user and may be used with wide array of Qubes VMs including standalone, appVMs, netVMs, Whonix, etc.
   • vm-boot-protect-root - Protects /home/user as above, automatic /rw executable deactivation, whitelisting, checksumming, deployment. Works with appVMs, netVMs, etc. that are template-based.

   CAUTION: The root option removes dirs specified in $privdirs; Default is /rw/config, /rw/usrlocal and /rw/bind-dirs.

3. Disabling the Qubes default passwordless-root is necessary for the above measures to work effectively. Here are two recommended ways (choose one):

   • Enabling auth prompt for sudo configures a simple yes/no prompt that appears in dom0.
   • Uninstall the qubes-core-agent-passwordless-root package from the template. After doing this, you will have to use qvm-run -u root from dom0 to run any VM commands as root.

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Usage

Operation is automatic, although particular configuration options such as hash checks are possible.

At the basic vm-boot-protect level, certain executable files in /home will be made immutable so PATH and alias cannot be used to hijack commands like su and sudo, nor can impostor apps autostart whenever a VM starts. This prevents normal-privilege attacks from gaining persistence at startup.

At the vm-boot-protect-root level, the $privdirs paths will be renamed as backups, effectively removing them from the VM startup. Then whitelisting, hash/checksumming and deployment are done (if configured). This protects VM startup from attacks that had previously achieved privilege escalation.

Configuration

Add files to /etc/default/vms in the template to enable the following features...

Hashes/Checksums are checked in ../vms/vms.all.SHA and ../vms/$vmname.SHA files. File paths contained in them must be absolute. See man page for sha256sum -c.

Whitelists are checked in ../vms/vms.all.whitelist and ../vms/$vmname.whitelist files, and file paths contained in them must start with /rw/.

Deployment files are copied recursively from ../vms/vms.all/rw/ and ../vms/$vmname/rw/ dirs. Example is to place the .bashrc file in /etc/default/vms/vms.all/rw/home/user/.bashrc

Limitations

The vm-boot-protect concept relies mostly on the guest operating system's own defenses, with one added advantage of root volume non-persistence provided by the Qubes template system. This means that attacks which damage/exploit the private filesystem itself or quickly re-exploit network vulnerabilities could conceivably still persist at startup. Otherwise, protecting the init/autostart files should result in Qubes template-based VMs that boot 'cleanly' with much less chance of being affected by malware initially. Even if malware persists in a VM, it should be possible to run other apps and terminals without interference if malware has not escalated to root (admittedly, a big 'if').

Repeated running of some apps such as Firefox, Chrome, LibreOffice, PDF viewers, online games, etc. may allow malware to persist in a VM; this is not only because of the complexity of the formats handled by such apps, but also because of settings contained in javascript or which specify shell commands to be executed by the app.

Further, if the user configures a vulnerable app to run at startup, this introduces a malware persistence risk -- although not to the VM's whole execution environment if no privilege escalation is available to the attacker.

Notes

• The service name has been changed from vm-sudo-protect in pre-release to vm-boot-protect. The install script will automatically try to disable the old service.

• Currently if a vm-boot-protect check fails there is no immediate way to alert the user at startup. The VM will attempt to shutdown instead. See issue #7 for discussion.

• All the user-writable startup files in /home should be protected by the immutable flag; See issue #9 if you notice an omission or other problem. An extra step of disabling the flag using sudo chattr -i whenever the user wants to modify these startup files.

Releases

• v0.8.0 Adds protection to /rw, file SHA checksums, whitelists, deployment
• v0.2.0 Protects /home/user files and dirs

See also:

AppArmor Profiles