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.
such a great idea, i have not seen this before. back in my solaris admin days, we used to keep config stuff version controlled locally like this with rcs; found it super useful for quickly answering "what changed, and how" during incidents (whereas just looking for modified files and fetching backups was a slow ordeal)
Honestly I prefer running Ansible for that. Once you have a boilerplate set up the overhead is minimal and you don't have to fight each specific program's config file syntax just to figure out how to do comments.
> 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.
Probably because there's nothing that says only users in wheel (assuming your OS/distro even has that group; some don't) can sudo. You can grant any user with any group membership access to sudo, either full access, or restricted to only certain commands.
If the package was set up to install /usr/bin/sudo so it was only runnable by members of the wheel group, that wouldn't work.
It's worth noting that the reason why your OS/distro doesn't have or doesn't respect wheel is largely down to RMS opposing it[0], instead favoring people trading the root password around to unauthorized users.
It's also worth noting that the Coreutils `su` is no longer in use by anyone, and that the `su` from the shadow-package absolutely checks for wheel. It's even configurable if you haven't enabled PAM by configuring `SU_WHEEL_ONLY` in your login.defs. And with PAM you configure that via PAM.
Hell, not even GNU distros like GNU Guix, Parabola, nor Trisquel follow RMS' opinions on this anymore.
Having a wheel group that is allowed to run any command with su rights is the default setup, but it's not the only one.
I have used sudo a lot of times to allow a specific user to run exactly one command with elevated rights. In those cases they weren't in the wheel group.
Actually retristricting defined commands to defined sudoers should be one of the main use cases of sudo. This could be done as well via ssh config but one would need a lot of keys if you don not want a wrapper (and rewrite sudo all over)
If you are really thinking security, elevating a standard user seems bad practice to anyways. It is rather I guess a way to protect the user to do `rm -rf /` accidentally. On the other end adding an another layer of obscurity is practically adding a bit of security against script kiddies. But if that is of concern one could also rename the sudo binary.
One last thing the SSH trick might be interesting is the portability but in this case I would rather go via a standard TCP socket.
Has anyone prepared a list of distributions indicating the default sudo setup comparing to each other? I'd be interested to see the defaults for each distro as a factor to consider.
It’s at the very least incompatible with *some^ hypothetical sudo configurations. It’s probably a good hardening practice if you know how sudo is going to set up on the machine.
In addition to being the default name for the admin group in Debian, the name has some history:
> [from slang ‘big wheel’ for a powerful person] A person who has an active wheel bit. “We need to find a wheel to unwedge the hung tape drives.” The traditional name of security group zero in BSD (to which the major system-internal users like root belong) is ‘wheel’.
> The term was invented on the TENEX operating system, and carried over to TOPS-20, XEROX-IFS, and others. The state of being in a privileged logon is sometimes called wheel mode. This term entered the Unix culture from TWENEX in the mid-1980s and has been gaining popularity there (esp. at university sites).
The wheel group is just a regular user group, its just the name Debian gives the group with admin permissions.
It's no different to any other user group on linux systems and you could replace the name wheel with admin, freethinker, systemdestroyer or whatever else you wanna call it.
Not really! In modern Linux specifically it's just a regular user group, but it's the de-facto standard name of the "administrator" group - users who can escalate to root privileges.
You might not even have wheel anymore; Debian just calls it "sudo" now.
The downside of this is that if you have your system set up to automatically install package updates, then it will start failing, which might kill all automatic updates.
On Debian, for example, I have unattended-upgrades set up to automatically install security updates. sudo is reasonably likely to have updates for security reasons.
There's also a command argument that can be provided in the authorized keys setup, which can force connections with a particular key to hit an entry-point application.
note, that even with ForcedCommand, sshd still executes ~/.ssh/rc in the user's name, so she can execute arbitrary command once she can write the rc file (unless disabled by PermitUserRC).
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.
As opposed to running background processes as root...?
This is just mindless dogma at this point. You're going to need something to elevate permissions, and setuid is as good of a scheme as any. ssh or run0 are not magic and just as "vulnerable" as setuid or anything else. Any of these schemes are "security holes" if you abuse it.
The argument is, that in case of sudo, the caller (potential attacker) controls the environment. In many cases, software or libraries are not made with a hostile environment in mind. Think of LD_PRELOAD or PATH ...
When there's a daemon running in the background, the attack surface is more commonly understood. The environment is not under attacker control.
Libraries rarely treat data from socket as "trusted" but often blindly trust environment variables, or stdin/stdout/stderr.
That has nothing to do with setuid, and is a very different argument from an unqualified "suid feature is huge security hole."
sudo etc. already clear much of the environment. And you're going to want to keep some of it because people expect "sudo foo" to work (which you can't do without PATH).
That is a furphy, because both tools are also used non-interactively.
If you forced me to choose one to remove, I’d delete ssh in many cases. Anything production that isn’t bare-metal is a candidate for never allowing a remote terminal. Easiest with cloud instances since they’re almost completely disposable, but many sites still don’t have the stomach/discipline for it.
I don't see how two sshd daemons and two sessions is less complicated.
Yes, removing sudo is one fewer moving part, but sshd is a much larger moving part than sudo. (If you think sudo is a larger moving part than it should be, I'd agree, and you can use doas instead.)
Regardless, the vast majority of my sudo usage is on my local machine, so there's no sshd involved at all.
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.
I would assume if you has to use SSH or sudo you've already lost. I've been working with people where we just completely lock down the VM or Container. They only allow necessary flow of traffic and are managed entirely from golden builds. If you need to make changes or fix something it is a new vm or container.
This premise is incorrect: SSH doesn't need to be an suid binary because it's already running as root, and then SSH creates a new environment for the user, exactly like sudo does, but with all the added complexity and overhead (and surface) of privileged network access.
To be clear, I love SSH and we even run a userify instance to distribute keys, but juts comparatively the surface area of the ssh daemon alone is greater than sudo alone.
(however, even with the extra complexity, you might trust the history of portable OpenSSH more than sudo, and that's a good, but different, conversation to have also.)
But the area under control by the invoking user is data over one socket vs the whole calling environment e.g. environment vars, local files. Surely that counts for something.
We've got root passwords set on, IIRC, all of our systems. They're long, random, and can only be entered through the console on the VGA port or the IPMI console.
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.
> If ‘sudo’ is properly configured running bash or anything that allows command execution (vim, eMacs, etc) is disallowed.
Keep in mind that this is borderline impossible to enforce unless your goal is just to stop the most common ways of accidentally breaking the policy. A list of commands that allows breaking out into a full shell includes: less, apt, man, nano, wget & many more.
This made me chuckle. Apple influencing the way Emacs is capitalized (pun intended) versus RMS's stance on Free Software couldn't be further apart I think.
You're correct there! Wrote that up on my tiny Apple device and really couldn't be bothered to correct Apple's spellcheck. Text editing from a 5in touchscreen is very painful.
> 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.
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.
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)
I'm not sure I agree with this argument. Sure you can say theoretically it's one less account that could be compromised, but in practice I see a bunch of caveats.
1. If we allow password based logins, there will be many orders of magnitude more login attempts to root than any other user. So if you have to allow password based logins, you pretty much never want to allow root login.
2. If we disallow password based logins, a user account would be as save as a root login, except again that the root account is the much more valuable target so will get much more attention. I also do see the relevance of cronjobs (root does run them as well) and naturally no user that has sudo privileges should be be running network exposed services.
3. In cases were admin rights have to be shared amongst multiple users, are you going to share the same key for all users (probably not a good idea) or give every user a separate key (making key management a bit of a nightmare, user management is much easier).
4. As you pointed out yourself sudo gives you much more fine-grained control over commands that can be run.
> 3. In cases were admin rights have to be shared amongst multiple users, are you going to share the same key for all users (probably not a good idea) or give every user a separate key (making key management a bit of a nightmare, user management is much easier).
To solve the key management nightmare, short-lived SSH certificates can be used to map an identity to a shared user account. Hashicorp Vault is one option for issuing such certificates, but there are other alternatives 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
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.
[0] https://etckeeper.branchable.com/
such a great idea, i have not seen this before. back in my solaris admin days, we used to keep config stuff version controlled locally like this with rcs; found it super useful for quickly answering "what changed, and how" during incidents (whereas just looking for modified files and fetching backups was a slow ordeal)
I like Chezmoi for this, and also use it to manage my home directory.
Plain ol’ git is also nice in a pinch.
Honestly I prefer running Ansible for that. Once you have a boilerplate set up the overhead is minimal and you don't have to fight each specific program's config file syntax just to figure out how to do comments.
> 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.
Probably because there's nothing that says only users in wheel (assuming your OS/distro even has that group; some don't) can sudo. You can grant any user with any group membership access to sudo, either full access, or restricted to only certain commands.
If the package was set up to install /usr/bin/sudo so it was only runnable by members of the wheel group, that wouldn't work.
It's worth noting that the reason why your OS/distro doesn't have or doesn't respect wheel is largely down to RMS opposing it[0], instead favoring people trading the root password around to unauthorized users.
[0] https://web.archive.org/web/20070603191229/http://www.gnu.or...
It's also worth noting that the Coreutils `su` is no longer in use by anyone, and that the `su` from the shadow-package absolutely checks for wheel. It's even configurable if you haven't enabled PAM by configuring `SU_WHEEL_ONLY` in your login.defs. And with PAM you configure that via PAM.
Hell, not even GNU distros like GNU Guix, Parabola, nor Trisquel follow RMS' opinions on this anymore.
Not all distros use `alias su='sudo -i'`. Ubuntu does. Debian does not. Not sure about others.
Having a wheel group that is allowed to run any command with su rights is the default setup, but it's not the only one.
I have used sudo a lot of times to allow a specific user to run exactly one command with elevated rights. In those cases they weren't in the wheel group.
Actually retristricting defined commands to defined sudoers should be one of the main use cases of sudo. This could be done as well via ssh config but one would need a lot of keys if you don not want a wrapper (and rewrite sudo all over)
If you are really thinking security, elevating a standard user seems bad practice to anyways. It is rather I guess a way to protect the user to do `rm -rf /` accidentally. On the other end adding an another layer of obscurity is practically adding a bit of security against script kiddies. But if that is of concern one could also rename the sudo binary.
One last thing the SSH trick might be interesting is the portability but in this case I would rather go via a standard TCP socket.
Has anyone prepared a list of distributions indicating the default sudo setup comparing to each other? I'd be interested to see the defaults for each distro as a factor to consider.
It’s at the very least incompatible with *some^ hypothetical sudo configurations. It’s probably a good hardening practice if you know how sudo is going to set up on the machine.
Not every user who uses sudo is admin or elevates to root.
I've seen a wheel or sudo group often enough to think it's common.
Pardon my ignorance, but I have to ask for explanation of what the wheel group is and does. I'm aware that this might open a can of worms.
In addition to being the default name for the admin group in Debian, the name has some history:
> [from slang ‘big wheel’ for a powerful person] A person who has an active wheel bit. “We need to find a wheel to unwedge the hung tape drives.” The traditional name of security group zero in BSD (to which the major system-internal users like root belong) is ‘wheel’.
> The term was invented on the TENEX operating system, and carried over to TOPS-20, XEROX-IFS, and others. The state of being in a privileged logon is sometimes called wheel mode. This term entered the Unix culture from TWENEX in the mid-1980s and has been gaining popularity there (esp. at university sites).
http://www.catb.org/~esr/jargon/html/W/wheel.html
Great bit of history, thanks!
The wheel group is just a regular user group, its just the name Debian gives the group with admin permissions.
It's no different to any other user group on linux systems and you could replace the name wheel with admin, freethinker, systemdestroyer or whatever else you wanna call it.
Not really! In modern Linux specifically it's just a regular user group, but it's the de-facto standard name of the "administrator" group - users who can escalate to root privileges.
You might not even have wheel anymore; Debian just calls it "sudo" now.
Maybe also make /usr/bin/sudo immutable? would that help prevent a package manager from messing with it? I think so.
The downside of this is that if you have your system set up to automatically install package updates, then it will start failing, which might kill all automatic updates.
On Debian, for example, I have unattended-upgrades set up to automatically install security updates. sudo is reasonably likely to have updates for security reasons.
There are multiple ways to "override" a file managed by dpkg:
https://wiki.debian.org/DebianAlternatives
https://www.debian.org/doc/debian-policy/ap-pkg-diversions.h...
How would you do that?
lsattr - for reading attributes chattr - for setting them
You need the `i` attribute. But this is filesystem dependent. Anyway protecting the `sudo` binary from package managers is a so-so idea.
man chattr
> And since the sshd approach doesn't allow you to restrict root access to only certain commands [...]
The ForcedCommand infrastructure.
There's also a command argument that can be provided in the authorized keys setup, which can force connections with a particular key to hit an entry-point application.
This is the ForcedCommand mechanism.
note, that even with ForcedCommand, sshd still executes ~/.ssh/rc in the user's name, so she can execute arbitrary command once she can write the rc file (unless disabled by PermitUserRC).
shameless plug: you can prevent this by https://github.com/bAndie91/tools/tree/master/ssh-groupcomma...
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.
> IMO. suid feature is huge security hole.
As opposed to running background processes as root...?
This is just mindless dogma at this point. You're going to need something to elevate permissions, and setuid is as good of a scheme as any. ssh or run0 are not magic and just as "vulnerable" as setuid or anything else. Any of these schemes are "security holes" if you abuse it.
The argument is, that in case of sudo, the caller (potential attacker) controls the environment. In many cases, software or libraries are not made with a hostile environment in mind. Think of LD_PRELOAD or PATH ...
When there's a daemon running in the background, the attack surface is more commonly understood. The environment is not under attacker control.
Libraries rarely treat data from socket as "trusted" but often blindly trust environment variables, or stdin/stdout/stderr.
That has nothing to do with setuid, and is a very different argument from an unqualified "suid feature is huge security hole."
sudo etc. already clear much of the environment. And you're going to want to keep some of it because people expect "sudo foo" to work (which you can't do without PATH).
"List of Unix binaries that can be used to bypass local security restrictions" (2023) https://news.ycombinator.com/item?id=36637980
"Fedora 40 Plans To Unify /usr/bin and /usr/sbin" (2024) https://news.ycombinator.com/item?id=38757975 ; a find expression to locate files with the setuid and setgid bits, setcap,
man run0: https://www.freedesktop.org/software/systemd/man/devel/run0....
Except when physically logged in via console you're already using ssh before using sudo.
So the complexity you describe is already there.
sudo removed is one less moving part in the end.
That is a furphy, because both tools are also used non-interactively.
If you forced me to choose one to remove, I’d delete ssh in many cases. Anything production that isn’t bare-metal is a candidate for never allowing a remote terminal. Easiest with cloud instances since they’re almost completely disposable, but many sites still don’t have the stomach/discipline for it.
TIL: "furphy" https://en.m.wikipedia.org/wiki/Furphy
I don't see how two sshd daemons and two sessions is less complicated.
Yes, removing sudo is one fewer moving part, but sshd is a much larger moving part than sudo. (If you think sudo is a larger moving part than it should be, I'd agree, and you can use doas instead.)
Regardless, the vast majority of my sudo usage is on my local machine, so there's no sshd involved at all.
Isn't this what systemd run0 is now doing?
- https://mastodon.social/@pid_eins/112353324518585654why must systemd re-invent everything?
Am I missing something?
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.
I would assume if you has to use SSH or sudo you've already lost. I've been working with people where we just completely lock down the VM or Container. They only allow necessary flow of traffic and are managed entirely from golden builds. If you need to make changes or fix something it is a new vm or container.
This premise is incorrect: SSH doesn't need to be an suid binary because it's already running as root, and then SSH creates a new environment for the user, exactly like sudo does, but with all the added complexity and overhead (and surface) of privileged network access.
To be clear, I love SSH and we even run a userify instance to distribute keys, but juts comparatively the surface area of the ssh daemon alone is greater than sudo alone.
(however, even with the extra complexity, you might trust the history of portable OpenSSH more than sudo, and that's a good, but different, conversation to have also.)
But the area under control by the invoking user is data over one socket vs the whole calling environment e.g. environment vars, local files. Surely that counts for something.
Unfortunately SSH has to do all that too. :(
...why not just su then?
root would need a defined password, which opens up other security concerns
Even if you allow passwordless su for users in the wheel group?
That's extremely dangerous. Any software running as a wheel user can escalate privileges willy nilly.
they can also access your ssh private keys
In theory, those ssh private keys are password protected.
In practice, maybe not.
They were stored in the user’s yubikeys (or similar) in this example.
If you do that you deserve what you get
Do what!?
plzno
We've got root passwords set on, IIRC, all of our systems. They're long, random, and can only be entered through the console on the VGA port or the IPMI console.
su is also a suid binary, no? It is probably a lot less complex than sudo.
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.
I can agree with that, though admit to being guilty of using sudo bash far more often than I should.
I honestly thought they’d be using ssh that way (single command at a time), though I’m still not sure to what security end.
If ‘sudo’ is properly configured running bash or anything that allows command execution (vim, eMacs, etc) is disallowed.
Also, may I introduce you to the ‘sudo -i’ option.
> If ‘sudo’ is properly configured running bash or anything that allows command execution (vim, eMacs, etc) is disallowed.
Keep in mind that this is borderline impossible to enforce unless your goal is just to stop the most common ways of accidentally breaking the policy. A list of commands that allows breaking out into a full shell includes: less, apt, man, nano, wget & many more.
https://gtfobins.github.io/#+shell
> eMacs
This made me chuckle. Apple influencing the way Emacs is capitalized (pun intended) versus RMS's stance on Free Software couldn't be further apart I think.
You're correct there! Wrote that up on my tiny Apple device and really couldn't be bothered to correct Apple's spellcheck. Text editing from a 5in touchscreen is very painful.
I sudo bash a lot as well. Some times I regret it when I try to figure out what the hell I did months ago. :)
It's comical to see the sudo codebase mentioned in the same breath as increasing auditability here
Auditd and pam_tty_audit can take care of all your auditing needs
Sure! All part of layered controls and reporting.
> 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.
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.
Psst… privilege has no letter D
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)
I'm not sure I agree with this argument. Sure you can say theoretically it's one less account that could be compromised, but in practice I see a bunch of caveats.
1. If we allow password based logins, there will be many orders of magnitude more login attempts to root than any other user. So if you have to allow password based logins, you pretty much never want to allow root login.
2. If we disallow password based logins, a user account would be as save as a root login, except again that the root account is the much more valuable target so will get much more attention. I also do see the relevance of cronjobs (root does run them as well) and naturally no user that has sudo privileges should be be running network exposed services.
3. In cases were admin rights have to be shared amongst multiple users, are you going to share the same key for all users (probably not a good idea) or give every user a separate key (making key management a bit of a nightmare, user management is much easier).
4. As you pointed out yourself sudo gives you much more fine-grained control over commands that can be run.
> 3. In cases were admin rights have to be shared amongst multiple users, are you going to share the same key for all users (probably not a good idea) or give every user a separate key (making key management a bit of a nightmare, user management is much easier).
To solve the key management nightmare, short-lived SSH certificates can be used to map an identity to a shared user account. Hashicorp Vault is one option for issuing such certificates, but there are other alternatives as well.
https://docs.redhat.com/en/documentation/red_hat_enterprise_....
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.
As I run a system similar to the one used in TFA I'll give my take...
> 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.
> Much harder to pull local privilege escalation exploits.
That's not certain. sshd is way bigger than sudo, so chances of it having an exploitable bug seem higher.
> You can't even login at failsave console.
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.
> Your system should have a root password set, for logins via console.
TFA says that he's prefixing his password hash with '!', making login with a root password impossible (including at the console).
Hence GP's question.
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.
SSH can do some of that with ForceCommand, though I agree that's not as flexible/precise.
This is a similar idea to run0 by Systemd: https://news.itsfoss.com/systemd-run0/
And run0 isn't roll-your-own. Its audited and probably better than home grown.
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.
Bug report about the shell indirection:
https://bugzilla.mindrot.org/show_bug.cgi?id=2283
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.
Sounds like what you have is similar to the idea of a bastion host, even if not quite the same.
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.
> if you need to be root, then login as root via console
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.
Additionally, you need to rotate and distribute the new root password to all root users when you want to remove access for someone.
You can have multiple accounts with uid/gid 0 (and can set up smart card or u2f login too if you want).
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.
> I changed the root password
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
Only with GNU su. A portable though limited replacement would be something like
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.
Ouch, that's a major security issue if configured that way. That's something I'll want to add to my hardening checks.
Good stuff. Imagine this though: ssh as user access control using a multiuser system such as gnu/linux
byw everyone should be using ed25519 or at least 2048+
Fixing things that aren't broken. Changing things just because they can be changed. Sometimes boring and stagnant is good.
I wouldn’t go as far to say sudo is broken but have you considered why would people create things such as doas and run0 if sudo is good enough?
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
This reminds me a little of plam 9 and inferno in treating local resources and network resources with a uniform protocol
Usenix LISA (now called SRECon) had a paper about this technique in 2004:
https://www.usenix.org/legacy/publications/library/proceedin...
Those who ignore Usenix are doomed to repeat it … 20 years later.
[dead]
It seems like a way for Fed.Gov to know everything we do on our computers.
Kill it with fire.
They have some rule hidden somewhere that communications through sockets is less private than things in the terminal.