Re: vsftpd download backdoored

[Solar Designer <solar () openwall com>]

On Mon, Jul 04, 2011 at 11:04:00PM -0500, HD Moore wrote:
> This copy is backdoored and has mtime Feb-15-2011. Chris didn't reply
> when I asked him for a copy from his master (old/vsftpd-2.3.4.tar.gz).
>
> http://download.polytechnic.edu.na/pub2/vsftpd/vsftpd-2.3.4.tar.gz

This is very helpful, thank you!  How did you find it?

So, I failed to get this server to give me ctime (looked at HTTP headers
and also tried several FTP commands), and the mtime is Feb 15.  We could
ask the server admins for the ctime.

However, inside the archive we see 2011-06-30 14:15 UTC on the top-level
directory, and 2011-06-30 13:46 on the .o files.  This suggests that the
backdoored tarball was put in place no earlier than 2011-06-30 14:15 UTC,
although that's using the intruder's system time, which might not be
accurate. ;-)

> ... I am saying that for this to become as widespread as the mtime in
> the mirror above indicates, it would be incredible for distros like
> Debian to not notice it, as they verify the hash of the tarball. This
> indicates that the mtime in the mirror above was forged (since the hash
> is indeed wrong), but the real question is how this mirror obtained the
> copy.
>
> Was the mirror compromised? Was a rsync job used against the real
> server, in which case the mtime was preserved? I couldn't find any
> public copies with the backdoored checksum, but one of the metasploit
> contributors pointed me to the link above.

My guess is that the mirror is automatically updated, perhaps nightly,
and not necessarily via rsync.  It is possible to transfer/preserve the
mtime via ftp and http as well - typical mirror programs do that.

> I would like to believe the exposure was limited to 1-3 days, but the
> mirror above casts doubt on this.

Looks like it was 3 days, actually.

Thanks,

Alexander