scapy (1)

scapy [options]

This manual page documents briefly the scapy tool.

scapy is a powerful interactive packet manipulation tool, packet generator, network scanner, network discovery, packet sniffer, etc. It can for the moment replace hping, parts of nmap, arpspoof, arp-sk, arping, tcpdump, tshark, p0f, ...

scapy uses the python interpreter as a command board. That means that you can use directly python language (assign variables, use loops, define functions, etc.) If you give a file as parameter when you run scapy, your session (variables, functions, intances, ...) will be saved when you leave the interpretor, and restored the next time you launch scapy.

The idea is simple. Those kind of tools do two things : sending packets and receiving answers. That's what scapy does : you define a set of packets, it sends them, receives answers, matches requests with answers and returns a list of packet couples (request, answer) and a list of unmatched packets. This has the big advantage over tools like nmap or hping that an answer is not reduced to (open/closed/filtered), but is the whole packet.

On top of this can be build more high level functions, for example one that does traceroutes and give as a result only the start TTL of the request and the source IP of the answer. One that pings a whole network and gives the list of machines answering. One that does a portscan and returns a LaTeX report.

Options for scapy are:

-h

display usage

-d

increase log verbosity. Can be used many times.

-s FILE

use FILE to save/load session values (variables, functions, intances, ...)

-p PRESTART_FILE

use PRESTART_FILE instead of $HOME/.scapy_prestart.py as pre-startup file

-P

do not run prestart file

-c STARTUP_FILE

use STARTUP_FILE instead of $HOME/.scapy_startup.py as startup file

-C

do not run startup file

Only the vital commands to begin are listed here for the moment.

ls()

lists supported protocol layers. If a protocol layer is given as parameter, lists its fields and types of fields.

lsc()

lists some user commands. If a command is given as parameter, its documentation is displayed.

conf

this object contains the configuration.

$HOME/.scapy_prestart.py This file is run before scapy core is loaded. Only the \conf object is available. This file can be used to manipulate conf.load_layers list to choose which layers will be loaded:

conf.load_layers.remove("bluetooth")
conf.load_layers.append("new_layer")

$HOME/.scapy_startup.py This file is run after scapy is loaded. It can be used to configure some of the scapy behaviors:

conf.prog.pdfreader="xpdf"
split_layers(UDP,DNS)

More verbose examples are available at http://www.secdev.org/projects/scapy/demo.html Just run scapy and try the following commands in the interpreter.

Test the robustness of a network stack with invalid packets:

sr(IP(dst="172.16.1.1", ihl=2, options="\verb$\x02$", version=3)/ICMP())

Packet sniffing and dissection (with a bpf filter or thetereal-like output):

a=sniff(filter="tcp port 110")
a=sniff(prn = lambda x: x.display)

Sniffed packet reemission:

a=sniff(filter="tcp port 110")
sendp(a)

Pcap file packet reemission:

sendp(rdpcap("file.cap"))

Manual TCP traceroute:

sr(IP(dst="www.google.com", ttl=(1,30))/TCP(seq=RandInt(), sport=RandShort(), dport=dport)

Protocol scan:

sr(IP(dst="172.16.1.28", proto=(1,254)))

ARP ping:

srp(Ether(dst="ff:ff:ff:ff:ff:ff")/ARP(pdst="172.16.1.1/24"))

ACK scan:

sr(IP(dst="172.16.1.28")/TCP(dport=(1,1024), flags="A"))

Passive OS fingerprinting:

sniff(prn=prnp0f)

Active OS fingerprinting:

nmap_fp("172.16.1.232")

ARP cache poisonning:

sendp(Ether(dst=tmac)/ARP(op="who-has", psrc=victim, pdst=target))

Reporting:

report_ports("192.168.2.34", (20,30))

http://www.secdev.org/projects/scapy
http://trac.secdev.org/scapy

Does not give the right source IP for routes that use interface aliases.

May miss packets under heavy load.

Session saving is limited by Python ability to marshal objects. As a consequence, lambda functions and generators can't be saved, which seriously reduce usefulness of this feature.

BPF filters don't work on Point-to-point interfaces.

Philippe Biondi <[email protected]>

This manual page was written by Alberto Gonzalez Iniesta <[email protected]> and Philippe Biondi.