HTTP

Scapy supports the sending / receiving of HTTP packets natively.

HTTP 1.X

Note

Support for HTTP 1.X was added in 2.4.3, whereas HTTP 2.X was already in 2.4.0.

About HTTP 1.X

HTTP 1.X is a text protocol. Those are pretty unusual nowadays (HTTP 2.X is binary), therefore its implementation is very different.

For transmission purposes, HTTP 1.X frames are split in various fragments during the connection, which may or not have been encoded. This is explain over https://developer.mozilla.org/fr/docs/Web/HTTP/Headers/Transfer-Encoding

To summarize, the frames can be split in 3 different ways:

  • chunks: split in fragments called chunks that are preceded by their length. The end of a frame is marked by an empty chunk
  • using Content-Length: the header of the HTTP frame announces the total length of the frame
  • None of the above: the HTTP frame ends when the TCP stream ends / when a TCP push happens.

Moreover, each frame may be aditionnally compressed, depending on the algorithm specified in the HTTP header:

  • compress: compressed using LZW
  • deflate: compressed using ZLIB
  • gzip

Let’s have a look at what happens when you perform an HTTPRequest using Scapy’s TCP_client (explained below):

../_images/http_tcp.png

Once the first SYN/ACK is done, the connection is established. Scapy will send the HTTPRequest(), and the host will answer with HTTP fragments. Scapy will ACK each of those, and recompile them using TCPSession, like Wireshark does when it displays the answer frame.

HTTP 1.X in Scapy

Let’s list the module’s content:

>>> explore(scapy.layers.http)
Packets contained in scapy.layers.http:
Class       |Name
------------|-------------
HTTP        |HTTP 1
HTTPRequest |HTTP Request
HTTPResponse|HTTP Response

There are two frames available: HTTPRequest and HTTPResponse. The HTTP is only used during dissection, as a util to choose between the two. All common header fields should be supported.

  • Default HTTPRequest:
>>> HTTPRequest().show()
###[ HTTP Request ]###
  Method= 'GET'
  Path= '/'
  Http_Version= 'HTTP/1.1'
  A_IM= None
  Accept= None
  Accept_Charset= None
  Accept_Datetime= None
  Accept_Encoding= None
  [...]
  • Default HTTPResponse:
>>> HTTPResponse().show()
###[ HTTP Response ]###
  Http_Version= 'HTTP/1.1'
  Status_Code= '200'
  Reason_Phrase= 'OK'
  Accept_Patch43= None
  Accept_Ranges= None
  [...]

Use Scapy to send/receive HTTP 1.X

To handle this decompression, Scapy uses Sessions classes, more specifically the TCPSession class. You have several ways of using it:

sniff(session=TCPSession, [...]) TCP_client.tcplink(HTTP, host, 80)
Perform decompression / defragmentation
on all TCP streams simultaneously, but
only acts passively.
Acts as a TCP client: handles SYN/ACK,
and all TCP actions, but only creates
one stream.

Examples:

  • TCP_client.tcplink:

Send an HTTPRequest to www.secdev.org and write the result in a file:

load_layer("http")
req = HTTP()/HTTPRequest(
    Accept_Encoding=b'gzip, deflate',
    Cache_Control=b'no-cache',
    Connection=b'keep-alive',
    Host=b'www.secdev.org',
    Pragma=b'no-cache'
)
a = TCP_client.tcplink(HTTP, "www.secdev.org", 80)
answser = a.sr1(req)
a.close()
with open("www.secdev.org.html", "wb") as file:
    file.write(answser.load)

TCP_client.tcplink makes it feel like it only received one packet, but in reality it was recombined in TCPSession. If you performed a plain sniff(), you would have seen those packets.

This code is implemented in a utility function: http_request(), usable as so:

load_layer("http")
http_request("www.google.com", "/", display=True)

This will open the webpage in your default browser thanks to display=True.

  • sniff():

Dissect a pcap which contains a JPEG image that was sent over HTTP using chunks.

Note

The http_chunk.pcap.gz file is available in scapy/test/pcaps

load_layer("http")
pkts = sniff(offline="http_chunk.pcap.gz", session=TCPSession)
# a[29] is the HTTPResponse
with open("image.jpg", "wb") as file:
    file.write(pkts[29].load)

HTTP 2.X

The HTTP 2 documentation is available as a Jupyther notebook over here: HTTP 2 Tuto