multiple boot modes for better security: persistent user | live user | persistent secureadmin | persistent superadmin | persistent recovery mode

Development
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Update:

The plan solidified. See this wiki page:

Old post:

Related:

What about more boot modes:

  • persistent + root
  • persistent + noroot
  • live + root
  • live + noroot

Not all might make sense.

Think of noroot has “hardening” where we can do stuff like noexec, nosuid, no root/sudo possible at all.

boot mode: live + noroot
Could disable SUID easily since non-persistent.

boot mode: live + root
We already have that.

boot mode: persistent + root:
We already have that.

boot mode: persistent + noroot:
Could use (re-)mount to nosuid etc.

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I think they all have their place and the persistent non-root is alright for a default everyday use option. Users can boot into the root mode when needing to install software which is a rarely done action.

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For usability, when users open a terminal emulator, they could be told the current mode they booted into and be explained how to gain root.

And/or Whonix live mode indicator could be modified or another similar systray could be added which gives a graphical indication of root vs non-root mode.

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Activating “Qubes” VM hardening when the non-root option is enabled is a nice additional safety net that shouldn’t hurt usaibility since the target protected folders should not be relevant to a legit user running under this mode.

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boot mode: persistent home but readonly root

https://wiki.debian.org/ReadonlyRoot

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iirc I tried that once and it failed due to something systemd and Xorg not really working. The site is also not really maintained. Could eventually be made to work but the way Debian went is “read-only” + overlayfs for live systems. / (overlay) in this case is modifiable at runtime but nonpersistent.

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There is also overlayroot.

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At least two modes:

  • Boot without persistent user data (or no login as user) with system in persistent mode (to update).
  • Boot with noexec persistent user data and system in live mode for everything else.

If there is malware in user data you will have to go out of your way to run it after boot. Of course nobody can stop you if you pipe something evil to bash, but persistent user data should not be executed by accident.
For this to work though “data” could not be all of $HOME because of login scripts ~/.bashrc etc that are sourced.
Perhaps a subdirectory for persistent data which ~/.config etc can link into. This is how Tails works I believe though I haven’t used it recently.
From the point of view of ‘user’ should there be a difference between Whonix in live mode and Tails with persistent data?

Tor Browser is a problem because there is no clear separation between code and data or system and user. The user has to run it to update itself. I believe Tails has a setting for persistent bookmarks but not prefs.

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Yes. Problem. Using this forum thread for that: Tor Browser vs NOEXEC - Where should the Tor Browser folder be placed?

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Noexec doesn’t help much due to scripts not being covered by noexec. (See discussion at the top and Chromium OS Docs - Shell scripts & noexec mounts )

Better no login as user user then. Even noexec, there are settings folders such as XFCE settings folders and others which could (in theory?) be abused to exploit the system.

Better use [A] Safely Use Root Commands instead? Perhaps [A] should get its own boot option?

Not sure Whonix live mode should have an (optional) persistent folder. But kinda unrelated. It could be implemented later if there is such a feature request. For now nobody ever asked about it. Kinda independent from this forum thread.

This is the idea of

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What I mean is live mode with a folder shared through the VM, that would behave like Tails with a persistent volume. The data is just data and should not be automatically processed by anything, noexec is just to help prevent accidents. There should be clear separation between trusted user data (immutable) and untrusted user data (shared folder). I don’t think this requires anything from Whonix. Sorry I’m having a hard time sticking to a thread.
Live mode does not disable shared folders, is that something you’re thinking of? How does live mode work with another virtual drive /dev/sdb etc?
Are you talking about separate grub entries for each mode or flags that can be added to the kernel command line?
With custom entries you could e.g. blacklist vboxguest in persistent mode. But it sounds like live mode is not technically binding so it would be up to the host to ensure shared folder is not accessible while system disk is writable.
Perhaps an option on the grub line to disable root?
Related: is it possible to start a VM with a given grub entry?

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Live mode currently does not disable virtual machine shared folders.

Added to comparison table here:

And asked about it here just now:

Agreed. Data in virtual machine shared folder shouldn’t be processed by default. This is already the case. I wouldn’t know what would process it.

noexec for shared folder is a good idea. It is already noted here: (re-)mount home [and other?] with noexec (and nosuid [among other useful mount options]) for better security?

They’re not automatically mounted. A root user or malware with root rights could mount these and write to it. This is illustrated in the comparison table here: grub-live - boot an existing Host OS or VM into Live Mode

This could be parially taken care of (root user) by booting into non-root mode (this forum thread). A root exploit can always undo that though.

Yes, that’s the idea.

Indeed. Good point. Yes, this should be documented.
[A] Also when work on Whonix Host progressed, we could add a starter/script which will help the user with such configurations for better usability.

That’s what this very forum thread is for. Help welcome.

Possibly yes. Both, VirtualBox and KVM support serial console.

Once we have that working, this might be automated with a script. Related to [A].

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There is hopefully no execution going on but certainly some processing/parsing. Otherwise you would not see the mounted folder or its contents nor the attached device.

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Once there is plan, this might be available as a package quickly within a day or two or so. Planning on implementing this soonish.

How would I technically implement a no-root boot mode?

Idea 1)

  • at early boot time
  • use a systemd unit file
  • if a certain kernel boot parameter such as nosudo=1 is set
  • run as root: delgroup user sudo
  • Otherwise if a certain kernel boot parameter such as sudo=1 is set
    • run as root: addgroup user sudo
    • That seems a bit weird, insecure for those who already followed instructions Prevent Malware from Sniffing the Root Password. Those users wouldn’t want their user user account be added to group sudo behind their back.

Therefore perhaps the default should be swapped.

Idea 2)

  • New builds of Whonix come without any user account added to the group sudo by default.
  • How to handle existing users that upgrade? Removal of user from group sudo might be a bit intrusive?
  • If a certain kernel boot parameter such as nosudo=1 is set:
    • run as root: delgroup user sudo
  • If a certain kernel boot parameter such as sudo=1 is set:
    • run as root: addgroup user sudo

Might also clash with security-misc since security-misc will abort to install if there are no users in group sudo.

security-misc/security-misc.preinst at master ¡ Kicksecure/security-misc ¡ GitHub

We probably shouldn’t break root login for ssh (for server support, Kicksecure, non-Whonix).

(Already done: For security reasons the root account is locked and expired by default in Whonix ™ 15.0.0.3.6 and above.)

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Most users seem to prefer security anyway.

https://twitter.com/Whonix/status/1196137962888556544

Maybe make another poll specifically about root.

Root login via ssh should be disabled either way. Allowing someone to remotely login as root isn’t a good idea.

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That was about security vs customization. Also that was a really abstract questions. If users really understand what’s at stake, they might decide otherwise.

This is not so much customization. This is more about security vs inconvenience.

This is more about security vs stability / bad surprises. Upgrade → cannot use “sudo” anymore. Terminal-only users couldn’t even run “sudo reboot”.

Maybe. Well, Whonix / Kicksecure don’t come with openssh-server installed by default. OpenSSH root login allowed by default or not setting doesn’t change much. Should change anyhow? How? Modify files in /etc/ssh? There is no configuration snippet drop-in folder (“.d”). Seems really intrusive → dpkg interactive conflict resolution dialog

( Configuration Files - Kicksecure )

Users who have openssh-server installed and then install security-misc or some other package are a different case.

We had a case we didn’t foresee a case where a user got locked out from his own server: Is security-misc suitable for hardening bridges and relays? - #4 by minimal

We’re already locking su. (Restrict root access)

Some users don’t use sudo. Maybe we should tell them they should. Maybe sane to require that.

Now we’re considering to remove user user from group sudo through an upgrade.

I am not saying we shouldn’t do it. Just thinking it all through aloud.

How much security would we gain from that anyhow? Let’s assume most times users boot into user user with sudo disabled. Ok… Let’s say their user account gets comprised through a remote exploit. That malware would have a harder time to break out since no easy escalation to root level, kernel level. Let’s say the malware starts itself through ~/.bashsrc or any of the many dotfiles. Then the user wants to upgrade and reboots in sudo=1 mode. The user now enters its user user password and gains root rights by using sudo. Boom. Malware can hijack that / sniff the password and become root too. We don’t get that much security from that?

How do we prevent that? Rely on VirusForget? 1) doesn’t exist. 2) not sure it will be finished 3) not that great, might be holes, not sure yet.

Instead, I am re-thinking about the old idea of user admin as per this very post: Restrict root access - #14 by Patrick.

Yes, once the plan is getting more specific, this will be a good idea. (Specifically if going the user admin route.)

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Whonix comes preconfigured so root isn’t really needed for the average user for anything other than customization or debugging.

apt-get-update-plus has a sudoers exception for that.

There’s no need to use sudo for that anyway. Unprivileged users can still run /sbin/reboot. The only issue is that /sbin isn’t part of $PATH by default (an alias can be added for reboot if needed).

Best option seems to be using str_replace on the openssh config file. It’s a bit hacky but better than just replacing the entire file.

I don’t use ssh much so I don’t know if there’s any better option.

Or, just not include it in security-misc since Whonix doesn’t have ssh anyway. We can leave configuring specific applications to be the user’s job.

We can add a warning to sudo mode and inform the user of the consequences of what they’re doing.

Restricting sudo is a security advantage. The only problem is if the user messes it up themselves which isn’t really on us.

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Having boot modes

  • nosudo=1 → delgroup user sudo
  • sudo=1 → addgroup user sudo

wouldn’t improve security too much. At least wouldn’t help much for users who install some custom package every now and then. (They need to use sudo for that.) Let alone add custom (third party) APT sources list. (Requires root to edit sources.list.d.)
Mostly would help users who do follow Prevent Malware from Sniffing the Root Password.
(But these would not even want addgroup user sudo.)

Not sure it’s even worth it to implement boot modes nosudo=1 / sudo=1?

(Just called nosudo=1 / sudo=1 for discussion. Would be presented to user in better terminology.)

Comparison with Tails:
Tails boots always fresh, malware clean. Considered non-compromised.
(Just assuming it for sake of discussion not considering firmware trojans etc. When boot from read-only media boot.)
Tails boots by default without root access. Setting a root password is an opt-in. Tails an edge here.

There are kinda two paths there.

  • [1] Allowing more and more things (apt dist-upgrade, install packages from packages.debian.org) without need to gain root / entering sudo password. Android does that. Users can do a lot things there without root. For example, setting up VPNs.
  • [2] Make users boot into user admin.

These two are not really exclusive. [1] will always be limited. A lot effort to implement. Might never get there.

I typed too little. I meant, after users just run “sudo apt-get dist-upgrade” or “upgrade-nonroot” they can no longer use “sudo”. Kinda unexpected, breaking usability change. Considered unstable by users most likely.

That would mean “boot into user admin” is an OK solution too?

Sounds good.

Yes. However, it’s on us to provide easy, secure work flows. I think “boot into user admin” is a nice clear way to separate things. Will describe more clearly soon.

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An alternative solution would be to add removing the sudo group to the hardening guides instead of making boot modes.

I don’t like the sound of that too much. Android is really different from Debian. If we allow unprivileged users to install packages, an attacker can install whatever they want from the repos to add attack surface.

e.g. 1: attacker installs package with setuid binary → exploits vulnerability → gains priv esc.

e.g. 2: attacker installs kernel module from the repos which adds kernel attack surface → exploits vulnerability in new module.

Meanwhile android apps cannot add any new kernel attack surface or increase the chances of priv esc. All apps are fully sandboxed, running as different users with strict SELinux policies and seccomp filters. It isn’t really comparable.

The admin user is better but not the best. An attacker can still login as the admin user too.

Btw by “boot” do you mean “login” (as a user called “admin” with sudo privileges) or are you talking about a boot mode? I assume you meant “login”.

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