Re: vsFTPd remote code execution

[xD 0x41 <secn3t () gmail com>]

There is guides, like;

http://blog.up-link.ro/how-to-set-up-vsftpd-virtual-users-berkeley-db-pam/

wich is folwing this trend...to create a var/ftp/public or
var/ftp/user , wich is great...if your not running vsftpd...



On 16 December 2011 00:39, HI-TECH .
<isowarez.isowarez.isowarez () googlemail com> wrote:
> Hi Chris,
>
> Am 14. Dezember 2011 08:21 schrieb Chris Evans <scarybeasts () gmail com>:
> > On Tue, Dec 13, 2011 at 12:11 PM, HI-TECH .
> > <isowarez.isowarez.isowarez () googlemail com> wrote:
> > > Yes you are somewhat right, as this is the old discussion about if
> > > code execution inside an ftpd
> > > is a vulnerability itself or only local code execution. I have the
> > > opinion that an ftpd which does not allow to run code
> > > should restrict the user so, and if there is a way to execute code it
> > > it is a vulnerability.
> > > Take the example of a vsftpd configured for anonymous ftp and write
> > > access in /var/ftp.
> >
> > IIRC, vsftpd can refuse to start an anonymous session for the
> > misconfiguration where the root directory is writeable (to avoid
> > problems in the libc like this). I'll make sure it still works and
> > maybe check other paths such as /etc
>
> thats indeed true, nevertheless I have seen boxes in the wild
> with vsftpd running with anonymous and write access in
> /var/ftp, maybe because this security measure was built into
> vsftpd in newer versions ? I am not sure.
>
> > For local users, there's a configuration setting: "chroot_local_user".
> > The compiled-in default is false, and the man page cautions:
> > ---
> > .BR Warning:
> > This option has security implications, especially if the users have upload
> > permission, or shell access. Only enable if you know what you are doing.
> > ---
> >
> > I'm not uptodate with whether Linux distributions have turned this on
> > by default or not.
>
> I think it is not the default setting but many admins will make use of it in
> hosting environments.
> > vsftpd does have the concept of "virtual users". I'm not sure if it's
> > widely used but it seems that this type of user login would present
> > the biggest headache.
> >
> >
> > Amusingly, vsftpd already attempts to desist glibc from loading any
> > timezone files from inside the chroot() (see env_init) by warming up
> > the subsystem and even explicitly setting TZ in the environment. glibc
> > displeases me. Perhaps it's a gmtime() vs. localtime() issue -- I'm
> > curious to know if glibc still crashes if the setting
> > "use_localtime=YES" is used?
> I havent checked that but as you said in a private conversation
> cacheing the zoneinfo file through glibc beforehand makes the zoneinfo file
> usage disappear in my strace output.
> > I don't mind adding workarounds or avoidances for libc bugs (for
> > example, functions like regcomp, fnmatch have long been avoided). If
> > you had any clever ideas, I'm happy to put them in, otherwise it's a
> > case of waiting for the glibc updates.
>
> For me it is a miracle why this bug was not patched in glibc back in 2009.
>
> Here is the patch by you Chris I hope I can go ahead and post it here
> on full disclosure
> as this might get into a new release anyways (use at your own risk!):
>
> Add this to the very bottom of vsf_sysutil_tzset():
>
> ---snip---
>  p_tm = localtime(&the_time);
>  if (p_tm == NULL)
>  {
>   die("localtime #2");
>  }
>  p_tm = gmtime(&the_time);
>  if (p_tm == NULL)
>  {
>   die("gmtime");
>  }
> ---snip---
>
> Regards,
>
> Kingcope
> > Cheers
> > Chris
> >
> > > The attacker might
> > > execute code using the vulnerability without authentication
> > > credentials, or for example an attacker only has
> > > access to a user account configured for ftp.
> > > Basically you are right, vsftpd uses privsep so its a not so risky
> > > vulnerability.
> > >
> > > /Kingcope
> > >
> > > Am 13. Dezember 2011 20:56 schrieb Dan Rosenberg <dan.j.rosenberg () gmail com>:
> > > > > Anyone with an up2date linux local root which only makes use of syscalls? :>
> > > >
> > > > This is all fun stuff, and definitely worth looking into further, but
> > > > if you've got a local kernel exploit that you can trigger from inside
> > > > vsftpd, you don't need this (potential) vulnerability in vsftpd - you
> > > > already win.
> > > >
> > > > -Dan
> > >
> > > _______________________________________________
> > > Full-Disclosure - We believe in it.
> > > Charter: http://lists.grok.org.uk/full-disclosure-charter.html
> > > Hosted and sponsored by Secunia - http://secunia.com/
>
> _______________________________________________
> Full-Disclosure - We believe in it.
> Charter: http://lists.grok.org.uk/full-disclosure-charter.html
> Hosted and sponsored by Secunia - http://secunia.com/

_______________________________________________
Full-Disclosure - We believe in it.
Charter: http://lists.grok.org.uk/full-disclosure-charter.html
Hosted and sponsored by Secunia - http://secunia.com/