Sudo-rs' first security audit | Hacker News Reader

Sudo-rs' first security audit

ferrous-systems.com

62 pointsArgorak59 comments

> Description: The cargo release build does not strip symbols, so they will be included in the final binary. (..) Impact: Since the code is open source, there is not much information to be gained, but removing these symbols might make reverse engineering of the binary harder.

What a ridiculous finding.

I can try to steelman the argument. Sure, maybe "reverse engineering of the binary" is useless most of the time for an open source project because you can just look at the source code. But if there were hypothetically a memory corruption vulnerability in sudo-rs, then an attacker would want to identify the specific machine code corresponding to the vulnerable source, in order to determine how it could be exploited. That wouldn't be too hard to achieve without symbols, but symbols would definitely make it easier.

Except… even if the binary has symbols stripped, you can just `apt install sudo-rs-dbgsym`, or use debuginfod, to get the full debug info including symbols and DWARF records. Because distros provide that for all their packages. As a feature. To assist debugging.

Even if distros didn't distribute debug symbols, today's security best practices include reproducible builds, which means you should be able to rebuild the package yourself and get the exact same binary, plus the symbols.

So while it might save a tiny bit of disk space to strip the symbols, the security benefit is absolutely nil.

…Well, in theory anyway. In practice, Debian's sudo-rs package seems to be missing both a dbgsym package and reproducible build info. But that's a bug!

That is what "low" means as a vulnerability severity! "Low" means "you totally don't need to do anything about this".

The reported property does make the attacker's job slightly harder, after all, since they need to go and work out where the symbols are rather than just having them right there in front of them.

The problem with the report isn’t just that it’s minor. The problem is that it’s directionally wrong. If the change makes life even slightly harder for attackers, then it makes life harder to exactly the same extent for legitimate users trying to debug their programs. The fact that debuginfo is widely distributed demonstrates that distros prioritize the benefits of debuggability over the benefits of obscurity, and there’s no reason that weighting should be different in the small versus in the large. So, if security and debuggability were the only concerns, debuggability should win and distro binaries should never be stripped. It just so happens that there is an unrelated concern, disk space, that justifies stripping them anyway, but that doesn’t justify characterizing the lack of stripping as a security flaw, not even an incredibly minor one.

Come off it. That’s what the severity rating is for. Anyone used to reading these sorts of reports comes to expect these things. And someone saying “all you have to do, is simply…” doesn’t change the fact that there’s suddenly more effort involved.

You could also always compile it from source with the debug symbols even if it wasn't provided by a distro.

If you can apt-get stuff, why would you be trying to exploit sudo? Even assuming apt-get was the only thing you could run as root, that would essentially allow arbitrary filesystem changes anyway. Escalating to full root from that would be trivial.

You can do that on an identical system you have access to. Then you discover the necessary vulnerability and apply it on the target system.

You don’t need to be root to retrieve the debug symbols from apt if the debug symbols were in the apt repository

Something like

    apt-get download sudo-rs-dbgsym

    mkdir -p ~/tmp/

    dpkg -x sudo-rs-dbgsym.deb ~/tmp/

should provide what you need I think

> Even if distros didn't distribute debug symbols, today's security best practices include reproducible builds, which means you should be able to rebuild the package yourself and get the exact same binary, plus the symbols

Well, that’s why binary randomization/fuzzing is an important security research topic. If everyone would be running semantically identical, but not binary-identical programs, a ROP-based vulnerability would not be able to spread across computers, or in absence of the correct binary on the target device, it would be infeasible.

This is the very definition of security through obscurity. If everyone were running "semantically identical, but not binary-identical programs" there would be debugging tools to automatically patch your patches for each target device.

How would that work with fuzzing at the compiler step, say, inlining a non-critical function at a place in one place but not in the other?

This is a real security topic, don’t handwave it away without knowing about it.

The same way any decompilation works - By looking at patterns, understanding how the original compiler worked, and following the execution path as it runs. Antimalware analysts have been doing far more complex for many years, including packed, encrypted, and self-modifying code. It temporarily obfuscates what's going on, but execution tells all. Not that you'd need anything that advanced, when you have the source code and can compare possible fuzzed outputs.

ASLR is a real technique that can make targets harder to pop on the first try, giving you time to detect the problem. It does not prevent bugs from being exploited, at least not reliably and for long. This is not a real security topic, this is minor roadbumps, urban myth, and quackery.

So with some insane amount of reverse engineering you can exploit a vulnerability on a single instance of the target program, which same exploit won’t run on another.

You can, starting from essentially scratch, also create a vulnerability for a separate instance, but it literally stops the spreading of a same malware exploiting multiple computers. How is that not security, and just obscurity? Is this not a valid threat model?

No, it's not, and it's side effects, making cryptographic verification of your system state and installed programs impossible, make it not even worth discussing.

Verify the sources’ hash and randomize locally. Even better, distribute some intermediate format which is mostly compiled, but reproducible and locally randomize that.

I'm surprised that CLN-003 made the list even as low severity. It's intended to make reverse engineering of the binary harder, but the code is already freely accessible (and CLN-003 also acknowledges this).

That vulnerability seems like something added to adhere to the rule of 3. In at least Western culture, we have this ingrained thing for groups of 3 - for example Trinity, 3 point outline, 3 sentences in a paragraph etc.

It seems like this was picked to end up with 3 vulnerabilities so the security researchers can feel they did a complete job.

I see it as a note to be exhaustive. It’s the kind of thing if you don’t add it to your report, some smart ass WILL say something like « actually they forgot about the bin symbols, how could they miss this? ». There’s always someone like this.

The arbitrary delete vulnerability scared me at first, but are there really situations where a non-root user can create a new user??

In practice, I doubt it. But sudo offers highly granular permission controls. You can permit a user to only run certain commands as root. So it is a real vuln in the sense that if you give someone that ability, you've now given them more than intended.

I just ran tokei in the sudo-rs repository and there's over 28,000 lines of code not including whitespace. The Rust rewrite is a good step forward but we should really be asking ourselves if we need all this complexity in something so critical.

OpenBSD's doas is 108 lines of C. sudo and doas are not equivalent in functionality, but it shows how simple things can really be.

https://github.com/openbsd/src/blob/master/distrib/special/d...

Which parts are you thinking of removing? The goal is “to build a drop-in replacement for all common use cases of sudo” so the doas comparison doesn’t really follow.

The fabulous article mentions that, “sudo-rs only has 3 dependencies in its dependency graph” so maybe they could trade loc for deps but that doesn’t seem wise to me.

The audit found one moderate path traversal vulnerability which was also present in og sudo, so I’m not sure how your suggestion could be made practical.

> the doas comparison doesn’t really follow

The real question is, do you really need everything that sudo can do? Or would doas be sufficient?

On my FreeBSD servers, I install doas instead of sudo, and I have never once found myself missing any features in spite of having completely replaced sudo with doas on my FreeBSD servers.

Replaced as in, I no longer even have sudo installed on my FreeBSD servers. I switched from sudo to doas cold turkey years ago and haven’t looked back.

(On Linux I still use sudo, but that is simply because it comes pre-installed on the Linux distros I use so I haven’t bothered to install doas instead there.)

doas does exactly what I need; run the following command as root.

Right, I’d speculate that removing sudo for doas is a heavy but feasible lift at the distro level. But as I said elsethread, I’m also very interested in an as-safe-as-possible replacement between now and then. Removing the need entirely (as they are both conceptually broken) seems like a huge lift that’s probably not feasible without fundamental changes. Could it be done within POSIX? IDK but I’d guess not.

>Removing the need entirely (as they are both conceptually broken) seems like a huge lift that’s probably not feasible without fundamental changes

A sort of workaround is that you can log in as the desired user from a TTY. Of course, this gets tricky if you don't have physical access or a remote serial connection. And you probably wouldn't want to log in as root over SSH. I don't have real solutions in mind but it's ticking over in my head. Might have some ideas later on.

Aye, but then we are (I think) sharing credentials so we can both log in as the user with specific (read: elevated) permissions, and we lose any ability to know who the “real” person-user is on top. So it’s a different problem and we’re starting to talk about threat models and such..

> we lose any ability to know who the “real” person-user is on top

It's a complex topic probably best suited for discussion elsewhere, but do we even need to discern that anymore? Statistically most Linux systems running now are single-seat (as in, one real user).

A big corp with thousands of servers and employees might want to know this stuff for audit logging, but if employees have root access, they can already fake everything at ring 3. Big corps use security software that do that stuff in ring 0.

> if employees have root access

The main usecase of sudo over su (or suid binaries) is limited access (clear/re-run the mail queue - not reconfigure the mail daemon)

> Right, I’d speculate that removing sudo for doas is a heavy but feasible lift at the distro level.

Not that heavy a lift, at least as a default. AIUI Alpine switched to doas and moved sudo to the community repo, Arch supports both, Void supports both, and NixOS supports both. I wouldn't be surprised if there are more. Although, RHEL and SUSE would probably have a harder time because their customers are more likely to use sudo's long tail of features.

I’m only vaguely aware of Alpine but that’s pretty neat!

On FreeBSD the only thing I miss from sudo is the credential caching. I believe opendoas uses the same fairly portable method that sudo does. doas uses an OpenBSD-specific API.

Users and groups (auth/autz) via kerberos/ldap/active directory? Radius?

Not something "most users" would need - and probably handled in Pam, not sudo - but it's one thing that comes to mind.

>Which parts are you thinking of removing?

All of it. Seriously. doas demonstrates that sudo's primary function (running commands as another user) can be achieved in an order of magnitude less code and a significantly smaller attack surface.

90% of people don't need more than that, they don't need all the bells and whistles that sudo offers. We aren't in the 90s running on mainframes anymore.

As an aside, doas and sudo are conceptually broken from a security POV because the user's shell can be played with to elevate privileges. The real fix is dump doas and sudo entirely.

> conceptually broken

I agree, but the goal of this particular project is to make sudo as safe as possible. Within the stated goal, I don’t think significant LOC reduction is a feasible side quest.

Evangelizing the removal of sudo entirely is an interesting thought but given how widely deployed it is, I see a ton of value in having a sudo-rs stopgap between now and then.

Sorry, yes, I think this work is useful, but I also think that sysadmins and distro maintainers should be starting to think about dropping sudo in favour of something simpler. Those who need sudo can still reach for it.

> As an aside, doas and sudo are conceptually broken from a security POV because the user's shell can be played with to elevate privileges. The real fix is dump doas and sudo entirely.

Could you elaborate on this?

I think the one moderate vulnerability is an example of this. I have serious doubts about anyone having wanted to use that remove timestamps parameter in 2023. I'd be surprised if many people know it exists.

I more surprised an os would let you make a user with "../../" in the name though. I'd bet a heap of things would break. A while back I saw a guy name his windows desktop with an emoji and all sorts of software fell over.

Funny enough, my iphone has an emoji-only name and everything seems to work. I haven’t dared try with a machine I might want to ssh into though.

An emoji SSID can be hit and miss at times on what can detect it.

This is the actual device name, not just the network but that’s a good point. Tethering via the network manager GUI from a macbook works as expected with the network name same as device.

You got me curious so I checked arp -a which shows host name as a ?. Nmap also isn’t able to resolve the emoji name, neither is host, and I don’t think dns-sd either, though my mdns-fu is poor. I did test Terminal.app and I can echo an emoji so I’m guessing this is mostly a limitation of some of the ancient bsd utils that are packed with macos.

Thanks for the little rabbit hole!

>A while back I saw a guy name his windows desktop with an emoji and all sorts of software fell over.

Presumably all of it was written in languages built on old assumptions that a single character is one byte.

Or even that a character fits in 2 bytes, which is an easy mistake to make in languages like Java or C# that have a 16-bit `char` type

> I more surprised an os would let you make a user with "../../" in the name though.

There may be protections at some levels, but eventually a username is just an entry in a database. Admittedly, you do have to be on the other side of the airtight hatchway to do it, but modifying a line in /etc/passwd to have the field before the first ":" be "../../" is something the os can't really do much about once it's there.

It would be great to have an educational effort to that effect: if you don’t need sudo, use doas.

However, there are about six billion* things in existence right now that use sudo, so it’s a good idea to make sudo safer as well.

* rhetorical statistic

This doesn’t really change your conclusion, but I think that’s the wrong file. This is the real doas afaict: https://github.com/openbsd/src/blob/master/usr.bin/doas/doas...

Still just a tidy 1072 lines in that folder though.

I spent 5 minutes staring at your file trying to understand how on earth it does the things in the man page, but of course it doesn’t.

Thanks, you're right. I was surprised how sparse it was.

> we should really be asking ourselves if we need all this complexity in something so critical

What is all the complexity? What is all the extra functionality that sudo offers?

Good question, never used it.

sudoedit would be an example.

The ability to specify limited groups of commands that a subset of users can run, among other things.

The "Examples" section of the sudoers(5) man page is probably a good place to start to get an idea of the sorts of ways it can be configured

https://manpages.debian.org/bookworm/sudo/sudoers.5.en.html#...

So I inherited a machine in our lab last week (not a "production" or "test" server, just a random machine being used as a dev environment) and decided to change its hostname using systemd's hostnamectl. Subsequently every attempt to execute a command via 'sudo' caused it to hang for multiple tens of seconds before declaring it couldn't resolve the new (nonexistent, entirely local) hostname. This persisted until I eventually fixed the /etc/hosts file which the systemd thing had failed to do, and I still don't know why sudo wanted to look up this hostname over the network, or what bad things could've happened if one of the configured DNS servers had maliciously replied for it.

Have you checked the sudoers?

You can live a really simple life if you just stop using computers.

Simple isn't always better.

  CLN-001: relative path traversal vulnerability (moderate)

  During the audit, it came to light that the original sudo implementation was also affected by this issue, although with a lower security severity due to their use of the openat function.

I thought Rust was secure? How is it possible to write a program in Rust and still have the same security vulnerabilities, and actually be higher severity?

It's almost as if changing to an entirely new programming language and ecosystem isn't enough to make a secure application, and that you still have to try hard to secure it, regardless of the language.

How interesting.

This is a logic error whereas Rust delivers a way to drive down memory errors (assuming parent comment isn't mocking Rust advocates).

> It's almost as if changing to an entirely new programming language and ecosystem isn't enough to make a secure application, and that you still have to try hard to secure it, regardless of the language.

Has anyone argued that switching to Rust alone is sufficient to stop all security vulnerabilities?

Has anyone suggested that switching to Rust means you no longer need to do any work to write secure applications?

It seems to me you're arguing against a totally self-constructed straw-man.

That's a low quality troll. Nobody was saying rust solves all security issues.

It's hilarious that people invented an entirely new language to prevent a single attack vector. That's like learning Perl because it has no buffer overflows.

Come on, you're not even good at this. Have you considered doing something productive with your time instead?

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