TCP

Scapy is based on a stimulus/response model. This model does not work well for a TCP stack. On the other hand, quite often, the TCP stream is used as a tube to exchange messages that are stimulus/response-based.

Also, Scapy provides a way to describe network automata that can be used to create a TCP stack automaton.

There are many ways to use TCP with Scapy

Using the kernel’s TCP stack

Scapy provides a StreamSocket object that can transform a simple socket into a Scapy supersocket suitable for use with sr() command family.

>>> s=socket.socket()
>>> s.connect(("www.test.com",80))
>>> ss=StreamSocket(s,Raw)
>>> ss.sr1(Raw("GET /\r\n"))
Begin emission:
Finished to send 1 packets.
*
Received 1 packets, got 1 answers, remaining 0 packets
<Raw  load='<html>\r\n<head> ... >

Using kernel’s TCP stack means you’ll depend on your local firewall’s rules and the kernel’s routing table.

Scapy’s TCP client automaton

Scapy provides a simple TCP client automaton (no retransmits, no SAck, no timestamps, etc.). Automata can provide input and output in the shape of a supersocket (see Automata’s documentation).

Here is how to use Scapy’s TCP client automaton (needs at least Scapy v2.1.1).

Note

TCP_client.tcplink is a SuperSocket subclass, therefore all its functions (.sniff(), …) are available.

>>> s = TCP_client.tcplink(Raw, "www.test.com", 80)
>>> s.send("GET /\r\n")
7
>>> s.recv()
<Raw  load='<html>\r\n<head> ... >

Use external projects

  • muXTCP - Writing your own flexible Userland TCP/IP Stack - Ninja Style!!!
  • Integrating pynids