FIREWALK(8)FIREWALK(8)NAMEfirewalk - Active Reconnaissance Network Security Tool with Extreme
Prejudice
SYNOPSISfirewalk [-dhinprSsTtvx] target_gateway metric
DESCRIPTION
Firewalk is an active reconnaissance network security tool that
attempts to determine what layer 4 protocols a given IP forwarding
device will pass. Firewalk works by sending out TCP or UDP packets
with a TTL one greater than the targeted gateway. If the gateway
allows the traffic, it will forward the packets to the next hop where
they will expire and elicit an ICMP_TIME_EXCEEDED message. If the
gateway hostdoes not allow the traffic, it will likely drop the packets
on the floor and we will see no response.
To get the correct IP TTL that will result in expired packets one
beyond the gateway we need to ramp up hop-counts. We do this
in the same manner that traceroute works. Once we have the gateway
hopcount (at that point the scan is said to be `bound`) we can begin
our scan.
It is significant to note the fact that the ultimate destination host
does not have to be reached. It just needs to be somewhere down‐
stream, on the other side of the gateway, from the scanning host.
Please see http://www.wiley.com/cda/product/0,,0471205443,00.html for
more information on Firewalking and networking security tools in gen‐
eral.
COMMAND-LINE OPTIONS
If an option takes an argument, it procedes the option letter, with the
default in parenthesis.
-d 1-65535 (34434)
Specify the initial destination port to use during the
network discovery (aka TTL ramping) phase.
-h Program help.
-i interface_name
Specify interface to use. Only neccessary on multi-
homed machines.
-n Do not resolve IP addresses into hostnames. This saves
a DNS lookup and speeds the scans (mainly during network
discovery).
-P 1-2000 (0) Set a network writing pause which may be neccessary to
keep the program from flooding the network.
-p TCP, UDP (UDP)
Type of scan to perform.
-r Strict RFC 793 compliance. This only comes into play
when doing a TCP scan when your packets have an expire
vector of one and your metric host is one hop from your
gateway. Since the packets will reach their destina‐
tion, they will not expire, so we look for terminal
responses. For a TCP port in the listen state, we will
get back a SYN|ACK with the ACK as our SEQ + 1. How‐
ever, for a closed port, the response is stack depen‐
dent. If the host is RFC compliant we will receive an
RST|ACK with the ACK as our SEQ + 1. However, if the
host is not compliant (ie: microsoft) then the best we
can do is inverse tuple matching (which is the default).
-S 1-65535,... (1-130,139,1025)
Specify the ports for the scan. Ports may be specified
in ranges, delimited by dashes, and multiple ranges may
be specified, delimited by commas. Ommiting the termi‐
nating port number is shorthand for 65535.
-s 1-65535 (53)
Specify the source port for the scan (both phases).
-T 1-2000 (2) Network packet reading timeout. This is the time fire‐
walk will spend waiting for a response before timing
out.
-t 1-25 (1) Set the initial IP time to live (TTL) value. If a tar‐
get gateway is known to be (at least) n hops from the
source host, the TTL can be preloaded to facilitate a
faster scan.
-v Dump program version and exit.
-x expire vector (1)
The expire vector is the number of hops that the scan‐
ning probes will expire, past the gateway host. The
binding hopcount is the hopcount of the gateway + the
expire vector.
COMMAND-LINE EXAMPLES
CAVEATSSEE ALSOtraceroute(8), tracerx(8), pcap(3), libnet(3), dnet(3)AUTHOR
Mike D. Schiffman <mike@infonexus.com>
BUGS
Please send bug reports to mike@infonexus.com
firewalk 04.20.2002 FIREWALK(8)
