full-disclosure - qmail-auth vulnerability

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From: gerd-fd-list at cerb.de (Gerd Feiner)
Subject: qmail-auth vulnerability

from john simpson on bugtraq:

the qmail-smtpd-auth patch is a commonly used patch to qmail which
allows 
the qmail-smtpd program to support the AUTH extension, by specifying a 
"checkpassword" program on the command line. the homepage for the patch is:

http://members.elysium.pl/brush/qmail-smtpd-auth/

the patch modifies qmail-smtpd so that it can be called with three 
command-line parameters: the local host name (used for generating CRAM-MD5 
challenges), the checkpassword program itself, and a "dummy" program which 
is run by the checkpassword program after a successful authentication.

the "dummy" program is needed because checkpassword programs are designed 
for use in a POP3 or IMAP situation, where they would validate the user's 
credentials and then run the actual POP3 or IMAP server program.

the current version of the SMTP-AUTH patch contains a serious bug which can 
accidentally allow somebody who forgets one or more of the command line 
parameters to start running an open relay by accident. it has been reported 
in several places over the last week, including this message on the qmail 
mailing list:

http://marc.theaimsgroup.com/?l=qmail&m=105452174430616&w=2

if the user forgets the hostname parameter to qmail-smtpd and uses /bin/true 
as the dummy program (/bin/true is the suggested dummy program), they will 
actually be using /bin/true as the checkpassword program, which allows ANY 
combination of userid and password to use your server as a relay.

i have written a revision to the qmail-smtpd-auth patch which compensates 
for this common error by not supporting the AUTH command unless all three 
command line arguments are present.

the version 0.31 patch does not correctly check for this- with a missing 
command line argument, it ends up reading memory beyond the end of argv[], 
which is NOT filled with zeros- on most *nix systems it's actually the 
beginning of the environment block.

http://www.jms1.net/qmail/ has the modified "auth.patch" file available for 
download.

the changes i've made (actually CHECKING argc instead of assuming there will 
be something there) need to be incorporated into the qmail-smtpd-auth patch 
as soon as possible. the author of the patch seems to have not touched it 
since may 2002.

-- 
There are only 10 types of people in the world: 
Those who understand binary and those who don't ...

GPG-Key at: 
http://www.cerb.de/gerd/gpg-keys/pub.key
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