My main objection to this is just the added complexity. Instead of a single suid binary that reads a config file and calls exec(), now you have one binary that runs as root and listens on a UNIX socket, and another that talks to a UNIX socket; both of them have to do asymmetric crypto stuff.
It seems like the main argument against sudo/doas being presented is that you have a suid binary accessible to any user, and if there's a bug in it, an unauthorized user might be able to use it for privilege escalation. If that's really the main issue, then you can:
Add any sudoers to the wheel group, and there you go: only users that can sudo are allowed to even read the bytes of the file off disk, let alone execute them. This essentially gives you the same access-related security as the sshd approach (the UNIX socket there is set up to be only accessible to users in wheel), with much much much less complexity.
And since the sshd approach doesn't allow you to restrict root access to only certain commands (like sudo does), even if there is a bug in sudo that allows a user to bypass the command restrictions, that still gives no more access than the sshd approach.
If you are worried about your system package manager messing up the permissions on /usr/bin/sudo, you can put something in cron to fix them up that runs every hour or whatever you're comfortable with. Or you can uninstall sudo entirely, and manually install it from source to some other location. Then you have to maintain and upgrade it, manually, of course, unfortunately.
Personally I use etckeeper[0] to make sure all changes to /etc are tracked, either by software installs / upgrades, or done by humans. It's also great when needing to upgrade a machine to a newer release as you can create a patch file with all your local changes and apply that patch to a clean install and do a three way merge that will highlight all conflicts and keep you up to date and any changes required from one release to the next without having to research everything just in case.
> Add any sudoers to the wheel group, and there you go: only users that can sudo are allowed to even read the bytes of the file off disk, let alone execute them.
That's very sensible, I wonder why it's not the default setup everywhere.
If you could configure your linux kernel without suid support, that would be huge benefit for security, IMO. suid feature is huge security hole.
Whether fighting one particular suid binary worth it, is questionable indeed. But this is good direction. Another modern approach to this problem is run0 from systemd.
There's a new tool in systemd, called "run0". Or actually, it's not a new tool, it's actually the long existing tool "systemd-run", but when invoked under the "run0" name (via a symlink) it behaves a lot like a sudo clone. But with one key difference: it's *not* in fact SUID. Instead it just asks the service manager to invoke a command or shell under the target user's UID. It allocates a new PTY for that, and then shovels data back and forth from the originating TTY and this PTY. Or in other words: the target command is invoked in an isolated exec context, freshly forked off PID 1, without inheriting any context from the client (well, admittedly, we *do* propagate $TERM, but that's an explicit exception, i.e. allowlist rather than denylist).
One could say, "run0" is closer to behaviour of "ssh" than to "sudo", in many ways.
How is logging into ssh (sshd) AS root more secure than using sudo? I honestly don’t even know how dangerous that is because I’ve always been told to never allow it. I see here thought goes into preventing that for a remote user, so I’m not talking about that aspect of security here.
Maybe it has to do with #3 in the sudo limitations — I certainly don’t see any benefits vis-a-vis #1.
I totally get that this is an experiment, but I suspect it is more vulnerable than using sudo, not less (the open socket proxy looks interestingly vulnerable to a man in the middle attack).
Having said all that, I did learn some tricks old tools are capable of, so kudos for showing me something new.
The sudo binary is suid root / privileged and is exposed directly to the untrusted user. If anything goes wrong inside of sudo (with the user's entire environment as the surface area), it may be exploited.
The ssh approach does not expose a suid binary. Instead it uses the ssh network layer so it is no less secure than accessing ssh over a network, which is considered pretty secure.
A big part of sudo is that you should be running individual commands using sudo to increase auditability rather than simply running sudo bash or whatever.
> How is logging into ssh (sshd) AS root more secure than using sudo?
Article describes an additional SSH server listening on an Unix socket. The usual threat model about exposing root logins from the internet may not apply here.
The approach is comparing
- Theoretical configuration errors, or theoretical vulnerabilities that may or may not be there with
- Having a new daemon running (a new attack surface) which
- may also have configuration errors, or vulnerabilities as such
- and also removes a few layers of user based authorisation with a single root level
This approach is somehow considered more secure.
And in a rational way, and of course for any rational security perspective this can't be considered more secure, just different.
I'm skeptical of the approach in the linked article, but:
> I honestly don’t even know how dangerous that is because I’ve always been told to never allow it.
You've fallen for the FUD. In reality, logging in directly as root over remote SSH is strictly more secure than logging in as user over remote SSH and then using `sudo`.
If user@home uses ssh to root@server, then root@server is only compromised if user@home is compromised.
If user@home uses ssh to user@server then sudo to root@server, then root@server is compromised if either user@home or user@server is compromised. In particular, it is fairly common for user@server to be running some other software such as daemons or cronjobs. Please don't give out free root escalation (and often lateral movement due to password reuse) to anyone who manages to infect through those!
(This of course does not apply if sudo is used in whitelisted-commands-only mode and does not take either passwords or credentials fully accessible from the remote host)
The big advantage is if setuid and setgid support can be entirely removed. There are a bunch of special cases that have been added over the years to try to deal but increasing priviledges of a process is fundamentally more challenging in the unix security model than only ever lowering priviledges. Of course these days Linux has priviledge escalation via user namespaces as well.
So what happens if ssh (IIRC correctly in typical configurations it depends on network to start) fails to start at boot? You can't even login at failsave console. What does this actually buy us over sudo or su? Sure you avoid a setuid binary but instead you are now running a network service (even though only connected to a socket) with root priveledges.
Linux consoles (the ttys that appear over local display or remote-access KVM, or the ttyS* devices that appear over serial ports and IPMI SoL) do not use sudo or su. Those consoles use a program like `getty`, or a window-manager; all those programs are non-suid programs that are started as root.
Your system should have a root password set, for logins via console.
As far as I'm concerned, I use setuid/sudo for auditing. At this point, I don't really do multi-user/multi service boxes. Almost everything I have that's multi-tenant at this point is k8s and you can just use kubectl endpoint instead of ssh. But if you're allowed to log in, you're allowed to setuid to root. So for a k8s box, that's the platform infra team and access to the services on top is through the k8s permissions provider.
For the platform infra teams, if you just need something like metrics and logs, that's already off box. If you need to trigger some job or workflow, you can use the pipeline.
But when someone does log in and do root stuff, I want to have an audit log.
I actually can't think of a single box I own where someone with a login doesn't also have root for everything.
Obviously, I understand the services doing setuid thing, but in the case of services, you generally have systemd doing setuid to drop permissions instead of the other way around.
If you have access to the bootloadet, you can still set systems.unit=emergency.target, or init=/bin/bash, or rd.break=pre-pivot, or boot into a live-cd environment. All of the normal emergency options work.
For less fatal emergencies, I don't see anything that would tie this instance of sshd to tge network.
I think it’s a bit remiss to not include all of the downsides of this approach. sudo allows control over which groups can exercise which commands, what args those commands accept, subshell spawns, etc, etc, etc.
This approach loses a lot of this fine-grained control, and also relies on trusted keys, which are harder to manage than editing a sudoers file.
To see all the amazing things that sudo can do, I’d really recommend the Sudo Mastery book.
One of the issues with ssh is that spawning processes isn't part of the protocol. And it's a remote protocol, so it can't pass local resources to the child. So you can't pass a null-separated array of arguments, pass extra file descriptors or specify an executable.
Instead it just passes a string to a server-configured shell. So you need to shell-escape things and know which shell is running on the server side.
To use SSH as a proper sudo replacement it'd need something closer to posix_spawn as an extension.
100 000 times yes: I do something similar and I described that here on HN in a comment / comments in the past!
The way I do is a bit different...
I'm using a dedicated machine as my physical "SSH console" and that machine is living on a private LAN which is separated from the rest of the machines at home. It's on an unmanaged switch, using ethernet cables (but no trunk).
Then the only way to login is using SSH but, here's a little spin... with a Yubikey.
The desktop PC has its own firewall, only accepting SSH traffic in from the IP / MAC address of my "SSH console" (on the private LAN it's sharing with the SSH console... On the other physical LAN, my desktop can access the Internet).
Then the sshd daemon is configured to only allow pub/priv key logins, no password logins.
So basically when I need root, I boot up my "SSH console" (which boots ultra quickly for there's basically nothing on that machine), log in, hit the up arrow to get back the "ssh root@..." line, hit enter, press the Yubikey.
That "ssh console" and its keyboard is on my desk, always withing reaching distance.
iptables/nftables (on a private LAN moreover, physically separated from the other private LAN) + sshd: you judge if this is more or less secure than sudo binaries / su.
As to the "why", I'd answer "because I can". I did set that up such a long time ago that I don't even remember when I did. I think I started toying with that idea two years ago and I've been using it ever since. Zero problem. Not a single issue.
This is an elegant solution to the problem. We don't need to treat users as children, but at the same time we should avoid potential foot guns with sensible defaults. I'd argue that even `su` is not needed, if you need to be root, then login as root via console. This is as close as possible to logging into root from the console tty.
I did something similar a decade ago (well without the UNIX socket bit, but just a separate sshd listening on localhost only and also no need to deal with SCM_RIGHTS). Nothing good or bad came out of it. I simply got bored and didn't bother porting this setup to the next machine.
This is not a solution, it's a workaround.
One that breaks with ( outdated ) system design doctrines and therefore is likely to spawn more cans of worms and will certainly increase the amount of technical debt at present.
One issue I see with this is Single User Mode (aka recovery mode in grub (or similar) boot loader). Now you can't login as root to recover from init (systemd) configuration issues without having alternate boot media to get you access. I know it might sound pedantic but I used just this feature two days ago while upgrading a machine to a newer Linux release (the upgrade introduced an issue with the systemd / netplan config that got systemd into a loop due to deprecated keywords in the netplan config).
If you want traditional single user mode that drops you to a root shell even though your root account is locked add SYSTEMD_SULOGIN_FORCE=1 to the environment of rescue.service and emergency.service (systemctl edit rescue.service). Of course that exact solution isn't always a good idea depending on the situation but in general that situation can be delt with differently from normal access while running correctly.
I've used ssh to localhost as a hack for a backup-to-external-drive script (using Borg iirc) where I wanted the source reading and backup writing to be done as different users. There may have been a more elegant solution but it worked well enough
kelnos|1 year ago
It seems like the main argument against sudo/doas being presented is that you have a suid binary accessible to any user, and if there's a bug in it, an unauthorized user might be able to use it for privilege escalation. If that's really the main issue, then you can:
Add any sudoers to the wheel group, and there you go: only users that can sudo are allowed to even read the bytes of the file off disk, let alone execute them. This essentially gives you the same access-related security as the sshd approach (the UNIX socket there is set up to be only accessible to users in wheel), with much much much less complexity.And since the sshd approach doesn't allow you to restrict root access to only certain commands (like sudo does), even if there is a bug in sudo that allows a user to bypass the command restrictions, that still gives no more access than the sshd approach.
If you are worried about your system package manager messing up the permissions on /usr/bin/sudo, you can put something in cron to fix them up that runs every hour or whatever you're comfortable with. Or you can uninstall sudo entirely, and manually install it from source to some other location. Then you have to maintain and upgrade it, manually, of course, unfortunately.
tankenmate|1 year ago
[0] https://etckeeper.branchable.com/
alexey-salmin|1 year ago
That's very sensible, I wonder why it's not the default setup everywhere.
euroderf|1 year ago
lttlrck|1 year ago
blueflow|1 year ago
The ForcedCommand infrastructure.
vbezhenar|1 year ago
Whether fighting one particular suid binary worth it, is questionable indeed. But this is good direction. Another modern approach to this problem is run0 from systemd.
guerby|1 year ago
So the complexity you describe is already there.
sudo removed is one less moving part in the end.
wooptoo|1 year ago
bandie91|1 year ago
aaaronic|1 year ago
How is logging into ssh (sshd) AS root more secure than using sudo? I honestly don’t even know how dangerous that is because I’ve always been told to never allow it. I see here thought goes into preventing that for a remote user, so I’m not talking about that aspect of security here.
Maybe it has to do with #3 in the sudo limitations — I certainly don’t see any benefits vis-a-vis #1.
I totally get that this is an experiment, but I suspect it is more vulnerable than using sudo, not less (the open socket proxy looks interestingly vulnerable to a man in the middle attack).
Having said all that, I did learn some tricks old tools are capable of, so kudos for showing me something new.
lmz|1 year ago
The ssh approach does not expose a suid binary. Instead it uses the ssh network layer so it is no less secure than accessing ssh over a network, which is considered pretty secure.
op00to|1 year ago
irusensei|1 year ago
Article describes an additional SSH server listening on an Unix socket. The usual threat model about exposing root logins from the internet may not apply here.
fsniper|1 year ago
This approach is somehow considered more secure.
And in a rational way, and of course for any rational security perspective this can't be considered more secure, just different.
o11c|1 year ago
> I honestly don’t even know how dangerous that is because I’ve always been told to never allow it.
You've fallen for the FUD. In reality, logging in directly as root over remote SSH is strictly more secure than logging in as user over remote SSH and then using `sudo`.
If user@home uses ssh to root@server, then root@server is only compromised if user@home is compromised.
If user@home uses ssh to user@server then sudo to root@server, then root@server is compromised if either user@home or user@server is compromised. In particular, it is fairly common for user@server to be running some other software such as daemons or cronjobs. Please don't give out free root escalation (and often lateral movement due to password reuse) to anyone who manages to infect through those!
(This of course does not apply if sudo is used in whitelisted-commands-only mode and does not take either passwords or credentials fully accessible from the remote host)
joveian|1 year ago
cycomanic|1 year ago
TacticalCoder|1 year ago
> So what happens if ssh (IIRC correctly in typical configurations it depends on network to start) fails to start at boot?
I do this for my main desktop. If the worse of the worse happen, I've got backup of everything (we all do right?) and I re-install the system.
What I mean is: what do you do when you SSD is dead? You can't even login at failsafe console either.
In 30 years of using Linux I've have hard disk die on me way more than I had my sshd daemon not starting. The ratio is even a divide-by-zero error.
Arguably if my OS had its sshd daemon randomly not starting, it'd be an indication to me that it's time to move to a more stable OS.
> What does this actually buy us over sudo or su?
Much harder to pull local privilege escalation exploits.
CaliforniaKarl|1 year ago
Linux consoles (the ttys that appear over local display or remote-access KVM, or the ttyS* devices that appear over serial ports and IPMI SoL) do not use sudo or su. Those consoles use a program like `getty`, or a window-manager; all those programs are non-suid programs that are started as root.
Your system should have a root password set, for logins via console.
jethro_tell|1 year ago
For the platform infra teams, if you just need something like metrics and logs, that's already off box. If you need to trigger some job or workflow, you can use the pipeline.
But when someone does log in and do root stuff, I want to have an audit log.
I actually can't think of a single box I own where someone with a login doesn't also have root for everything.
Obviously, I understand the services doing setuid thing, but in the case of services, you generally have systemd doing setuid to drop permissions instead of the other way around.
gizmo686|1 year ago
For less fatal emergencies, I don't see anything that would tie this instance of sshd to tge network.
iroddis|1 year ago
This approach loses a lot of this fine-grained control, and also relies on trusted keys, which are harder to manage than editing a sudoers file.
To see all the amazing things that sudo can do, I’d really recommend the Sudo Mastery book.
yjftsjthsd-h|1 year ago
hernantz|1 year ago
ape4|1 year ago
the8472|1 year ago
To use SSH as a proper sudo replacement it'd need something closer to posix_spawn as an extension.
jwilk|1 year ago
https://bugzilla.mindrot.org/show_bug.cgi?id=2283
TacticalCoder|1 year ago
The way I do is a bit different...
I'm using a dedicated machine as my physical "SSH console" and that machine is living on a private LAN which is separated from the rest of the machines at home. It's on an unmanaged switch, using ethernet cables (but no trunk).
Then the only way to login is using SSH but, here's a little spin... with a Yubikey.
The desktop PC has its own firewall, only accepting SSH traffic in from the IP / MAC address of my "SSH console" (on the private LAN it's sharing with the SSH console... On the other physical LAN, my desktop can access the Internet).
Then the sshd daemon is configured to only allow pub/priv key logins, no password logins.
So basically when I need root, I boot up my "SSH console" (which boots ultra quickly for there's basically nothing on that machine), log in, hit the up arrow to get back the "ssh root@..." line, hit enter, press the Yubikey.
That "ssh console" and its keyboard is on my desk, always withing reaching distance.
iptables/nftables (on a private LAN moreover, physically separated from the other private LAN) + sshd: you judge if this is more or less secure than sudo binaries / su.
As to the "why", I'd answer "because I can". I did set that up such a long time ago that I don't even remember when I did. I think I started toying with that idea two years ago and I've been using it ever since. Zero problem. Not a single issue.
r4indeer|1 year ago
mise_en_place|1 year ago
bogantech|1 year ago
1: This requires every user to have the root password, while sudo does not
2: If everyone just logs in as root there's no way to audit who actually logged in and did what.
kccqzy|1 year ago
coretx|1 year ago
dheera|1 year ago
If you're going to set a root password, you might as well just do this and if I'm not mistaken it accomplishes everything you want
philkrylov|1 year ago
tankenmate|1 year ago
joveian|1 year ago
gnuser|1 year ago
byw everyone should be using ed25519 or at least 2048+
xfitm3|1 year ago
irusensei|1 year ago
didntcheck|1 year ago
ketily|1 year ago
YesThatTom2|1 year ago
https://www.usenix.org/legacy/publications/library/proceedin...
Those who ignore Usenix are doomed to repeat it … 20 years later.
ChoHag|1 year ago
[deleted]
RecycledEle|1 year ago
Kill it with fire.
RecycledEle|1 year ago