February 15, 2002

Ettercap - remote root compromise

Author: JT Smith

NGSEC: "As it is said in ettercap's home page 'Ettercap is a multipurpose sniffer/interceptor/logger for switched LAN'. Due to improper use of the memcpy() function, anyone can crash ettercap and execute code as root user... This vulnerability only exists on Linux version because on *BSD and MacOSX ettercap only works on ethernets devices."

 Next Generation Security Technologies
                          http://www.ngsec.com
                            Security Advisory


       Title:   Ettercap, remote root compromise
          ID:   NGSEC-2002-1
 Application:   ettercap 0.6.3.1 and older (http://ettercap.sourceforge.net)
        Date:   05/02/2002
      Status:   Vendor Contacted, new fixed version released.
    Platform:   Linux on interfaces with MTU > 2000
      Author:   Fermín J. Serna 
    Location:   http://www.ngsec.com/docs/advisories/NGSEC-2002-1.txt


Overview:
---------

As it is said in ettercap's home page "Ettercap is a multipurpose 
sniffer/interceptor/logger for switched LAN". Due to improper use of the
memcpy() function, anyone can crash ettercap and execute code as root 
user.

Vulnerabiliy has been confirmed and exploited in ettercap's version 
0.6.3.1. Older versions maybe vulnerable too. 

This vulnerability only exists on Linux version because on *BSD and MacOSX 
ettercap only works on ethernets devices.

Technical description: 
----------------------

Ettercap is composed of decoders which looks for user, passwords, 
communities and stuff alike.

Several decoders (mysql, irc, ...) suffer the following problem:

   memcpy(collector, payload, data_to_ettercap->datalen);

Collector is declared as: 

    u_char collector[MAX_DATA];

Where MAX_DATA is:

  #define MAX_DATA 2000

Datalen is the data (after TCP/UDP header) length read from the interface.
So on interfaces where MTU is higher than 2000 you can exploit ettercap. 
Since normal ethernets have MTU:1500 this bug can not be exploited due to 
unsupported defragmentation in ettercap, but may be crashed with a forged 
packet (ip->tot_len > MAX_DATA). 

Here are common MTU and interface types:
 
    65535 Hyperchannel
    17914 16 Mbit/sec token ring
    8166  Token Bus (IEEE 802.4)
    4464  4 Mbit/sec token ring (IEEE 802.5)
    1500  Ethernet
    1500  PPP (typical; can vary widely)


Exploit for this vulnerability can be found at 

       http://www.ngsec.com/downloads/exploits/ettercap-x.c

Sample explotation could be also in loopback interfaces: MTU:16436

  piscis:~# ettercap -NszC -i lo &
[1] 21887
  piscis:~# ./ettercap-x 0 | nc localhost 3306
  ettercap-0.6.3.1 xploit by Fermín J. Serna 
Next Generation Security Technologies
  http://www.ngsec.com   

  punt!
  piscis:~# telnet localhost 36864
  Trying 127.0.0.1...
  Connected to localhost.
  Escape character is '^]'.
  id;
  uid=0(root) gid=0(root) groups=0(root),1(bin),2(daemon),3(sys),10(wheel)


Recomendations:
---------------

Upgrade to a newer ettercap version. 
Run ettercap on a secure environment.


More advisories at: http://www.ngsec.com/advisories/
PGP Key: http://www.ngsec.com/labs.asc

(c)Copyright 2002 NGSEC. All rights reserved.

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