ftpd security issue ?

Xin Li delphij at delphij.net
Mon Dec 5 19:49:00 UTC 2011

Hash: SHA1

On 12/05/11 11:44, Mike Tancsa wrote:
> On 11/30/2011 8:16 PM, Xin LI wrote:
>> On 11/30/11 17:01, Mike Tancsa wrote:
>>> On 11/30/2011 7:01 PM, Xin LI wrote:
>>>>> BTW. This vulnerability affects only configurations, where
>>>>>  /etc/ftpchroot exists or anonymous user is allowed to
>>>>> create files inside etc and lib dirs.
>>>> This doesn't seem to be typical configuration or no?
>>> I think in shared hosting environments it would be somewhat
>>> common. For annon ftp, I dont think the anon user would be able
>>> to create / write to a lib directory.
>>>> Will the attached patch fix the problem?
>>>> (I think libc should just refuse /etc/nsswitch.conf and
>>>> libraries if they are writable by others by the way)
>>> It does not seem to prevent the issue for me.  Using
>>> Przemyslaw program's,
>> Sorry I patched at the wrong place, this one should do.
>> Note however this is not sufficient to fix the problem, for
>> instance one can still upload .so's that run arbitrary code at
>> his privilege, which has to be addressed in libc.  I need some
>> time to play around with libc to really fix this one.
> Forgive the naive question, but is there a way to prevent a process
> (in this case proftpd) from loading a .so if the session is in a
> chrooted environment ?  Or if at the start of the process, is there
> a way to force the process to load a lib so that later on, it wont
> try and load the "bad" lib ?

Currently no (I thought you were in the cc list in my discussion with
kib@?).  My initial plan was simply rejecting .so's with wrong
permissions but in the discussion turns out that would not be
sufficient and we have also considered other ways to do it, e.g. have
a wrapper where one can disable them completely.  I have not a full
solution yet as the change would touch quite a lot of things in the
base system...

- -- 
Xin LI <delphij at delphij.net>	https://www.delphij.net/
FreeBSD - The Power to Serve!		Live free or die
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