Authentication Vulnerabilities in OpenBSD

https://www.openwall.com/lists/oss-security/2019/12/04/5

by jwilk • 7 years ago

179 90 7 years ago

openwall.com

zdw2• 7 years ago

Upstream eratta and binary patches to address these issues is available: https://www.openbsd.org/errata66.html

LeonM• 7 years ago

The patch is still fresh so it's not distributed to most mirrors yet.

In case syspatch doesn't appear to do anything, check your /etc/updateurl, set it to the OpenBSD CDN, then run again.

tptacek3• 7 years ago

Oh, wow, this is brutal. They're shelling out to a command line program to do authentication, and not catching the "-" metacharacter in the username they shell out with, so you can pass options to that program.

fluffything• 7 years ago

Yep, very cool.

akira2501• 7 years ago

That's why I like DBJs method. You still use a command line program, but you pass a filehandle that the authentication data can be read from.. this seems much safer than trying to parse and re-format that data as an intermediary. Also avoids any data leaks through the often unprotected 'cmdline'.

Is there some technical reason OpenBSD doesn't do this?

mjevans• 7 years ago

Probably historic compatibility. If making a breaking change this might be a good time to implement a design benefiting from decades of real world experiences.

k_sze3• 7 years ago

What does “DBJ” stand for?

jstewartmobile• 7 years ago

Thank God for DJB. His entire website should be required reading for software developers.

kbenson• 7 years ago

This feels like an old school vulnerability. Things like this were the norm in the 90's and early 2000's. It feels weird to see an exploit like this now in a large and well known project, and very weird for it to be in OpenBSD.

It just goes to show, as a user you can make informed choices in what software to use to reduce your security exposure, but that's not enough. You still need to pay attention to new problems that might pop up. No software is guaranteed to be safe in perpetuity.

conradev• 7 years ago

In a world where we harden all of the things and write code in memory safe languages maybe memory corruption will be the old school vulnerability and this type of thing will be all that is left

quotemstr2• 7 years ago

Yeah. It's a shame how few people invoking shell commands use tricks like "--" to suppress option parsing and "./*" to suppress bad globs. :-(

linusnext5• 7 years ago

The marriage operator is always a source of fun like this. So named as it's the end of options, and the beginning of arguments.

asveikau3• 7 years ago

They're shelling out to a command line program to do authentication

Interesting to track who exactly "they" might have been, as many commenters are saying this is uncharacteristic for OpenBSD.

Looking at the patch, the first OpenBSD commit of this file [1] is from 2000 and says "from BSDI" in the commit message, did fork()+execve() at that time, and the BSDI copyright comment says 1995-1997.

Probable to say more recent OpenBSD stuff is likely not written this way, but that they have baggage like this in the tree from earlier times.

[1] https://cvsweb.openbsd.org/src/lib/libc/gen/auth_subr.c?rev=...

anthk24• 7 years ago

Al of the 3 BSD's can be traced back to 386BSD and before, 4.4 BSD.

linusnext5• 7 years ago

There have been many bugs in NetBSD code that are found and fixed. Quite often these bugs are in code shared with OpenBSD, but you never see them list it as such, as they import said fixes from NetBSD.

edited: make verb plural.

notaplumber5• 7 years ago

We thank Theo de Raadt and the OpenBSD developers for their incredibly quick response: they published patches for these vulnerabilities less than 40 hours after our initial contact.

Awesome.

alberth• 7 years ago

Important quote:

“this vulnerability is remotely exploitable in smtpd, ldapd, and radiusd, but its real-world impact should be studied on a case-by-case basis. For example, sshd is not exploitable thanks to its defense-in-depth mechanisms.”

Edit: formatting.

procinct• 7 years ago

this vulnerability is remotely exploitable in smtpd, ldapd, and radiusd, but its real-world impact should be studied on a case-by-case basis. For example, sshd is not exploitable thanks to its defense-in-depth mechanisms.

Does this mean OpenBSD will have to update the tagline on their website that says "Only two remote holes in the default install, in a heck of a long time!"?

tptacek3• 7 years ago

Yes.

notaplumber5• 7 years ago

No.

anthk24• 7 years ago

How? Show me how can I, remotely:

- Login with no SSH account

- Enable SSH

- Change PF rules

- Change the smtpd config

- Enable radiusd/ldapd without being root

- Running Xenocara's xlock when is not available on servers and I have no permissions

notaplumber5• 7 years ago

Most of the issues are classified as Local privilege escalation, and none of the daemons mentioned are enabled by default, sshd can be enabled in the installer, but as the quote says "sshd is not exploitable thanks to its defense-in-depth mechanisms."

So, no. Still holds.

Worth pointing that Linux has had a rough week as well, this one is pretty bad: https://www.openwall.com/lists/oss-security/2019/12/02/2

Patch your systems.

naniwaduni• 7 years ago

Once again, the "in the default install" line should be read as "as long as you don't do anything interesting".

upofadown• 7 years ago

Smtpd (one of the mentioned daemons) is started in a default install. It is configured to do local mail delivery and can queue up remote deliveries for programs running on the system. It only connects to localhost and does not authenticate so this exploit would be irrelevant. If one did open an authenticated mail connection on an interface accessible to the world then the exploit would allow the system to be used as a spam relay.

Added: Just to be clear, this doesn't give any significant access to the system itself through smtpd even if it is configured to be remotely accessible. So not a possible remote hole. Dunno about other stuff.

anthk24• 7 years ago

Uh, a bug disclosed from the infamous FVWM guy with a great default config. This is amazing.

http://taviso.decsystem.org/img/screenshot.png

technion• 7 years ago

This discussion comes up a lot, and I'd make an opposing case. Rather than debating whether OpenBSD can reasonably say this - I'd suggest most Linux distributions could say it themselves if they so wanted.

Last time I installed CentOS the only port open on the firewall by default with OpenSSH after all.

gerdesj• 7 years ago

Yes, patch as often as you can but I note that link you provide looks like a local priv. escalation, ie you have to be able to login to the box in some way.

This OBSD bug is externally exploitable.

Why did you single out an obscure Linux bug? There are quite a few other OSs available apart from OBSD.

satanspastaroll• 7 years ago

One could also say that this has been a great week for Linux, since all these problems have been caught

anthk24• 7 years ago

By default PF doesn't allow shit from external connections, so no.

yellowapple2• 7 years ago

"Default install" would be the key phrase here. By that metric, no need to update the tagline; smtpd doesn't do much by default, and SSH has other safeguards, so apparently a default install wouldn't be substantially impacted.

Still sucks for those of us who, you know, actually use smtpd on OpenBSD as a mail server. Thankfully it's just my personal one and I can afford to comment out the line(s) that actually enable outbound SMTP relaying, but still.

keyle• 7 years ago

What's very cool about this to me is how well put this report is in layman's terms.

Also is this going to increment the "X remote vulnerabilities in X years"?

anthk24• 7 years ago

As long as you override a default PF install, go on. Because you can't. Even with a PF rule being set, you must set up smtpd.conf right.

Also no ldapd and radiusd is listening by default, and SSHD is secure by itself. And you are asked in the first install if you want to enable it at boot, btw.

juped2• 7 years ago

Worth noting that this vuln passes you through authentication as an almost certainly invalid user - I expect the devs to put in more username validity checks, like the one ssh has, to mitigate this class of issues in the future.

(The second vuln listed is less sexy but escalates you to a real group.)

anthk24• 7 years ago

/usr/X11R6/bin/xlock is installed by default

Most servers will not install Xenocara at all in order to avoid

most security and space issues, as a lot of them now are using

vmm(4) for testing purposes.

Also as xlock moved upsteeam, OpenBSD will stop importing xlock

and maybe the will implement a patched and pledge(4)d slock (with

some features such as passwd display as asterisks) as the

Xenocara's workstation locker.

If would not be weird at all. Today the default wm is FVWM because

of historical respect to BSD's/Unix, but the most common WM used

by OpenBSD fans is, by far, CWM, which came from evilwm.

As Xenocara was already a fork of X, having a patched slock as

"xenolock" would be the next logical step.

Because xlock(4) is a shitty security fest by itself. Not to

blame the OpenBSD developers, but the main project. It's full of

features and slock matches better the OpenBSD's philosophy.

adamrt2• 7 years ago

I'm a big OpenBSD fan, but the OpenBSD devs recommend you install Xenocara, otherwise its considered a non-default install.

linusnext5• 7 years ago

Yeah, the "it's secure as long as you don't use it for anything" gets old.

anthk24• 7 years ago

Well, if it's a CLI based server I'd doubt X would be needed at all.

OpenBSD Amsterdam (A well known provider in the circle of OpenBSD users) doesn't enable X by default on its autoinstall file:

https://openbsd.amsterdam/setup.html

EDIT: It enables xbase.tgz but not the rest.

snvzz• 7 years ago

Openbsd recommends installing all sets these days.

yellowapple2• 7 years ago

Yikes. This one just turned my mail server into an open relay (assuming any would-be attackers picked up on it running smtpd). Went ahead and shut off outbound mail delivery (so smtpd only accepts mail destined for my domain) until I can get this patched.

Kudos to the OpenBSD folks for getting a patch whipped up so quick, and thankfully SSH ain't affected, but Jesus.

themattress• 7 years ago

Tangential, but it appears openwall.com is on several of my pi hole blocklists. I'm guessing its because of the tools they offer?

gautamcgoel2• 7 years ago

So... are they gonna update the OpenBSD webpage to say "only three remote vulnerabilities in a heck of a long time?" Do these bugs represent a vulnerability to real systems deployed in the wild, or are they more of a theoretical threat?

anthk24• 7 years ago

Not remotely exploitable by default.

ben_bai3• 7 years ago

sshd is mentioned (1.5) exactly because sshd did catch this and refused login. So no, no remote exploit in the default install.

But it was close :)

rsecora• 7 years ago

This is the new -froot!!!

[1]http://seclab.cs.ucdavis.edu/projects/testing/vulner/18.html

[2]https://www.symantec.com/security_response/attacksignatures/...

Authentication Vulnerabilities in OpenBSD

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