scapy.sessions module

Sessions: decode flow of packets when sniffing

class scapy.sessions.DefaultSession(prn=None, store=False, supersession=None, *args, **karg)

Bases: object

Default session: no stream decoding

count

on_packet_received(pkt)

DEV: entry point. Will be called by sniff() for each received packet (that passes the filters).

prn

store

toPacketList()

class scapy.sessions.IPSession(*args, **kwargs)

Bases: scapy.sessions.DefaultSession

Defragment IP packets ‘on-the-flow’.

Usage: >>> sniff(session=IPSession)

on_packet_received(pkt)

DEV: entry point. Will be called by sniff() for each received packet (that passes the filters).

class scapy.sessions.StringBuffer

Bases: object

StringBuffer is an object used to re-order data received during a TCP transmission.

Each TCP fragment contains a sequence number, which marks (relatively to the first sequence number) the index of the data contained in the fragment.

If a TCP fragment is missed, this class will fill the missing space with zeros.

append(data, seq)

clear()

full()

class scapy.sessions.TCPSession(*args, **kwargs)

Bases: scapy.sessions.IPSession

A Session that matches seq/ack packets together to dissect special protocols, such as HTTP.

DEV: implement a class-function tcp_reassemble in your Packet class:

@classmethod
def tcp_reassemble(cls, data, metadata):
    # data = the reassembled data from the same request/flow
    # metadata = empty dictionary, that can be used to store data
    [...]
    # If the packet is available, return it. Otherwise don't.
    # Whenever you return a packet, the buffer will be discarded.
    return pkt
    # Otherwise, maybe store stuff in metadata, and return None,
    # as you need additional data.
    return None

A (hard to understand) example can be found in scapy/layers/http.py

fmt = 'TCP {IP:%IP.src%}{IPv6:%IPv6.src%}:%r,TCP.sport% > {IP:%IP.dst%}{IPv6:%IPv6.dst%}:%r,TCP.dport%'

on_packet_received(pkt)

Hook to the Sessions API: entry point of the dissection. This will defragment IP if necessary, then process to TCP reassembly.