Fernando J. Pereda’s blag

May 3, 2008

On cooperating and paludis vulnerability

Filed under: blag — Tags: , , , — Fernando J. Pereda @ 11:31 am

Note: This was already published in my old blag but planet and wordpress insist on publishing it again. Sorry.

A serious security issue in paludis was brought to my attention recently, and I feel I should make you all aware. Apparently someone, with root access to a machine, can gain root access by installing or editing paludis config files.

For those interested, this is how it happened (times are GMT+1):

22:34 <@ferdy> bonsaikitten: can you give me any details regarding that
 security bug in paludis?
22:35 <+bonsaikitten> ferdy: it's so obvious you should have found it already
22:37 <@ferdy> bonsaikitten: I should, but I probably haven't
22:37 <+bonsaikitten> ferdy: well, as I am a moron I'm unable to coherently explain :)
22:37 <@ferdy> bonsaikitten: I mean, depends on whether we are talking about
a real security issue or about something we should document to avoid people
shooting themselves in the foot
22:39 <@ferdy> bonsaikitten: is that all you are going to tell me?
22:39 <+bonsaikitten> ferdy: come on, it's obvious. You're supposed to be smart ...
22:39 * bonsaikitten is not in a mood to explain
22:40 <@ferdy> bonsaikitten: you aren't really talking about the paludisbuild issue, are you?
22:41 <+bonsaikitten> mmh no, that's a different one
22:41 <@ferdy> k
22:41 <@ferdy> bonsaikitten: what are we talking about?
22:42 <@ferdy> bonsaikitten: you don't need to explain it... just say, in general 
terms, what the issue is
22:50 <@ferdy> bonsaikitten: so? care to give any useful hint?
22:50 <+bonsaikitten> ferdy: doesn't happen in portage compatibility mode
22:51 <+bonsaikitten> but I blame the vodka, hard to explain when *burp* *giggle*
22:52 <@ferdy> bonsaikitten: what's the impact?
22:53 <+bonsaikitten> ferdy: depends on how annoying the other person is
22:54 <+bonsaikitten> ferdy: worst case random file modification
22:58 <@ferdy> bonsaikitten: and we already agreed that we aren't talking about
the paludisbuild issue, right?
22:59 <@ferdy> bonsaikitten: if we aren't, I'll need more hints....
23:05 <@ferdy> bonsaikitten: can I get an attack vector?
23:05 <@ferdy> that shouldn't need lots of explaining... I can figure out that
part myself
23:19 <@ferdy> bonsaikitten: have you got that attack vector for me?
23:24 <+bonsaikitten> ferdy: look at configuration files, maybe you notice that
there's some exquisit code execution possible there
23:29 <@ferdy> bonsaikitten: you mean those config files that only root can
edit? I must be missing something here
23:29 <+bonsaikitten> ferdy: you are :)
23:29 <+bonsaikitten> not much, and it's basically the same flaw bashrc is
for portage
23:29 <+bonsaikitten> only that bashrc is config_protect'ed ...
23:30 <@ferdy> bonsaikitten: but for a package to clover those files, it must be
in a repo root added, right?
23:31 <+bonsaikitten> someone in the package mangler group, but yes
23:35 <@ferdy> bonsaikitten: but if you can change those files in the first place,
why clover them by adding a malicious repo with a malicious package that changes
those files?
23:35 <+bonsaikitten> ferdy: because it's very subtle
23:36 <@ferdy> moreover, if you can already do that, why not just make the
package install whatever backdoor you want?
23:37 <@ferdy> I mean, it is subtle, but why would anyone go the 'convoluted'
route? he is already able to edit those files (since he had to add that repo)
23:38 <+bonsaikitten> 'cause only paludis is affected and you will find it very
hard to trace
23:38 <+bonsaikitten> that makes it so tempting ...
23:40 <+bonsaikitten> just don't be surprised if it suddenly unmerges itself :)
23:41 <@ferdy> yeah... well...
23:41 <@ferdy> bonsaikitten: mind if I disclose this vulnerability in
 planet.gentoo.org?
23:42 <+bonsaikitten> go ahead
23:42 <@ferdy> ta
23:42 <+bonsaikitten> 't is even on the features page of the package mangler :)

This is a good lesson to learn today:

If you can edit files owned by root in a machine, you can get root access to that machine.

So the bottom line is: There is no vulnerability, if you can mangle paludis config files, you are already root so you don’t need to edit a file to run any command you want. Another lesson one can learn by reading that log is how to be really cooperative.

Ah, and before someone with a need to use cheap psychology asks, the intention of this blag post is to stop the FUD.

— ferdy

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