Hi,
am I wrong or the mechanism that you implement is similar to the one
implemented in lft (Layer Four Traceroute http://pwhois.org/lft/ ) ?
From the homepage:
"LFT is the all-in-one traceroute tool because it can launch a
variety of different probes using both UDP and TCP layer-4 protocols.
For example, rather than only launching UDP probes in an attempt to
elicit ICMP "TTL exceeded" from hosts in the path, LFT can send TCP
SYN or FIN probes to target arbitrary services. Then, LFT listens for
"TTL exceeded" messages, TCP RST (reset), and various other
interesting heuristics from firewalls or other gateways in the path.
LFT also distinguishes between TCP-based protocols (source and
destination), which make its statistics slightly more realistic, and
gives a savvy user the ability to trace protocol routes, not just
layer-3 (IP) hops. With LFT's verbose output, much can be discovered
about a target network."
Ciao,
Alessandro
On Jan 7, 2007, at 12:53 AM, Michal Zalewski wrote:
I'd like to announce the availability of a free security
reconnaissance /
firewall bypassing tool called 0trace. This tool enables the user to
perform hop enumeration ("traceroute") within an established TCP
connection, such as a HTTP or SMTP session. This is opposed to sending
stray packets, as traceroute-type tools usually do.
The important benefit of using an established connection and
matching TCP
packets to send a TTL-based probe is that such traffic is happily
allowed
through by many stateful firewalls and other defenses without further
inspection (since it is related to an entry in the connection table).
I'm not aware of any public implementations of this technique, even
though
the concept itself is making rounds since 2000 or so; because of
this, I
thought it might be a good idea to give it a try.
[ Of course, I might be wrong, but Google seems to agree with my
assessment. A related use of this idea is 'firewalk' by Schiffman
and
Goldsmith, a tool to probe firewall ACLs; another utility called
'tcptraceroute' by Michael C. Toren implements TCP SYN probes,
but since
the tool does not ride an existing connection, it is less likely to
succeed (sometimes a handshake must be completed with the NAT device
before any traffic is forwarded). ]
A good example of the difference is www.ebay.com (66.135.192.124) - a
regular UDP/ICMP traceroute and tcptraceroute both end like this:
14 as-0-0.bbr1.SanJose1.Level3.net (64.159.1.133) ...
15 ae-12-53.car2.SanJose1.Level3.net (4.68.123.80) ...
16 * * *
17 * * *
18 * * *
Let's do the same using 0trace: we first manually telnet to
66.135.192.124
to port 80, then execute: './0trace.sh eth0 66.135.192.124', and
finally
enter 'GET / HTTP/1.0' (followed by a single, not two newlines) to
solicit
some client-server traffic but keep the session alive for the
couple of
seconds 0trace needs to complete the probe.
The output is as follows:
10 80.91.249.14
11 213.248.65.210
12 213.248.83.66
13 4.68.110.81
14 4.68.97.33
15 64.159.1.130
16 4.68.123.48
17 166.90.140.134 <---
18 10.6.1.166 <--- new data
19 10.6.1.70 <---
Target reached.
The last three lines reveal firewalled infrastructure, including
private
addresses used on the inside of the company. This is obviously an
important piece of information as far as penetration testing is
concerned.
Of course, 0trace won't work everywhere and all the time. The tool
will
not produce interesting results in the following situations:
- Target's firewall drops all outgoing ICMP messages,
- Target's firewall does TTL or full-packet rewriting,
- There's an application layer proxy / load balancer in the way
(Akamai, in-house LBs, etc),
- There's no notable layer 3 infrastructure behind the firewall.
The tool also has a fairly distinctive TCP signature, and as such,
it can
be detected by IDS/IPS systems.
Enough chatter - the tool is available here (Linux version):
http://lcamtuf.coredump.cx/soft/0trace.tgz
Note: this is a 30-minute hack that involves C code coupled with a
cheesy
shellscript. It may not work on non-Linux systems, and may fail on
some
Linuxes, too. It could be improved in a number of ways - so if you
like
it, rewrite it.
Many thanks for Robert Swiecki (www.swiecki.net) for forcing me to
finally give this idea some thought and develop this piece.
Cheers,
/mz
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