[olug] more secure FTP server?

Tony Gies tony.gies at gruppe86.net
Tue Aug 13 02:58:23 UTC 2013


Getting FTP passwords jacked is extremely common and in the vast majority
of cases the culprit is end user malware. There are a couple prolific
strains that shim the Windows TCP/IP stack and sniff passwords (which FTP
transmits in plain text), and a couple more that read saved passwords from
common client software such as Filezilla and SmartFTP. In both cases, they
then typically transmit the stolen credentials to the attacker, and the
actual attack (usually adding Javascript droppers to any HTML file that is
accessible to the FTP user) is carried out by a drone machine on a botnet
or something like that (which is why you might have seen an unexpected
connection from a foreign country).

The best advice I can give you, the preferred course of action, is to not
use FTP. FTP is a junky old protocol that provides no security. It is
low-hanging fruit and a favored target of script kiddies and botnet
operators. If you run FTP and have any number of users above about 2 you
will constantly be on the defensive against stuff like this.

Instead, use SFTP. SFTP is an SSH-based protocol, so if you are running
SSH, you are probably already running it -- if not, it's a one-liner config
edit to enable it. Most client FTP software supports it; in Filezilla you
can change your saved FTP connection profiles to SFTP connections by
clicking a radio button. It operates over SSH so it is fully encrypted
end-to-end, and the jerks who bingoed your FTP server don't know/don't care
about it and don't target it like they do FTP. It also works with Pluggable
Authentication Modules the same way SSH does, so you can add multi-factor
authentication e.g. Google Authenticator into your login flow pretty easily.

If you want to continue to run FTP, the best defense against this is to
educate your end users: Keep your Windows machine virus-free, NEVER save
your password in your FTP client, don't use the same password for FTP as
for anything else because it flies across the network in clear text, etc.
You might also take some preventative measures like generous blacklisting
of foreign IP ranges your users aren't likely to log in from (or just
default-deny connections and whitelist end user IPs instead), set up FTP
over SSL, and add some kind of two-factor auth to VSFTP (which I'm told is
possible but I haven't messed with it, and I don't know how good client
support for it is).
On Aug 12, 2013 9:07 PM, "Lou Duchez" <lou at paprikash.com> wrote:

> ... I think maybe I spoke too soon -- VSFTPD seems to do a fine job of
> logging when I test it myself.  I had assumed it was a brute-force attack
> because the IP that the hack originated from is in Bavaria, but as far as I
> can tell, a brute-force attack would have been logged and Fail2Ban would
> have shut that down (that's what happened when I tested it myself).
> Malware on a user machine?  Packet sniffer?  All I can do is talk to end
> users, change the passwords, and try to lock the FTP down by IP.
>  So one of my Web sites got hacked via FTP.  Looking into it, here is the
>> problem.  I am running VSFTPD, and I am also running Fail2Ban to monitor
>> the VSFTPD log and detect failed login attempts.  It's a good system.  It's
>> a nearly flawless system.  The one flaw in this is, apparently, VSFTPD
>> doesn't bother to write much of anything to the log(s) when there are
>> errant login attempts, so Fail2Ban doesn't have anything to work with.
>> Does anyone know how to make VSFTPD more talkative in the case of failed
>> logins?  Or can anyone recommend a better FTP server, one that bothers to
>> log these things properly?
>> I realize that there are other measures I can take too, such as limiting
>> the IPs, changing the port, and not using FTP except when nothing else will
>> do.  And I'm looking into that.  but I'd also like to be running a good FTP
>> server.
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