Re: fingerd

[Steven L Baur <steve@miranova.com>]

snow  writes:

>> > Couple of things you can do:
>> >     2.  Install a more secure "fingerd" such that it only
>> >         allows "finger `userid@node.domain`" instead of
>> >         "finger `@node.domain`".

>     cfingerd can be gotten from:

cfingerd is not a safe program.  It must run as root, and has some big
problems.

Date: Wed, 18 Sep 1996 18:34:43 +0200 (MET DST)
From: Janos Farkas <chexum@shadow.banki.hu>
To: Administrador da Rede <admrede@opensite.com.br>
cc: linux-security@tarsier.cv.nrao.edu
Subject: Re: Finger Doubt
Message-ID: <Pine.LNX.3.95.960918181033.2523A-100000@shadow.banki.hu>


Howdy people!

On Tue, 17 Sep 1996, Administrador da Rede wrote:
> I use the newest version of cfinger, setted to not allow general finger, just
> specific ones. Does anyone knows how this person did that ? I hope I can
> find out, otherwise, bye bye finger service.

Badly.

I have sent the author a letter, but never got any reply back (it's 3
months later now!), so I just take the opportunity to warn the public
against its use.

Excerpts from the source (1.2.3, older versions have been a bit more
directly broken, now it has root privs only at the moments it shouldn't
have.)

	"This daemon must be run as root!"

[And unfortunately, does..]

...
	unlink ("/tmp/fslist");
...
        sprintf(st, "%s | tail +2 >> /tmp/fslist",
            prog_config.finger_program);
        ...
	system(st);

A similarly terrible one some lines later:

	system("cat /tmp/fslist | sort > /tmp/fslist.sort");

As it stands, it can allow any local user to destroy any file on the
system, including partition tables on disks.  Please someone correct me if
I am wrong, I tried this with cfingerd-1.2.2 and it allowed me to do bad
things.

I was a bit disappointed by the lack of any reply from the author, so I
think I am now justified to tell that

if anyone installed cfingerd (about 1.1 or later) on his system, disable
it IMMEDIATELY, until at least the author clarifies this bug in a new
version.  The current version is BAD.

However if you just need a finger daemon, you may take a look at xfingerd,
at
ftp://ftp.banki.hu:/pub/xfingerd/xfingerd-0.1.tar.gz
which is the one I wrote when I got desperate about cfingerd. (If you take
a look at its date stamp, you can see that cfingerd is long broken..)  I
too can't garantee that it's good for you, but it at least doesn't require
to be run as root, which is why I started being against cfingerd.

I hope this note finds everyone concerned.

Janos


-- 
steve@miranova.com baur
Unsolicited commercial e-mail will be billed at $250/message.
Real men aren't afraid to use chains on icy roads.