I want to write an application layer sniffer (SMTP/ftp/http).
Based on my searchs, first (and perhaps hardest!) step is to reassemble the tcp stream of the sniffed connections.
Indeed, what I need is something like the "follow TCP stream" option of wireshark, but I need a tool which do it on live interface and automatically. As I know, Tshark can extract TCP streams data from the saved pcap files automatically (link) but not from live interfaces. Can Tshark do it on live interfaces???
As I know, TCPflow can do exactly what I want, however, it can not handle IP defragmentation and SSL connections (I want to analyse the SSL content in the case I have the server private key).
Finally, I also try bro network monitor. Although it provides the list of TCP connections (conn.log), I was not able to get TCP connections contents.
Any suggestion about mentioned tools or any other useful tool is welcome.
Thanks in advance, Dan.
perl Net::Inspect library might help you. It also comes with a tcpudpflow which can write tcp and udp flows into separate files, similar to tcpflow. It works on pcap files or can do live captures. The library handles IP fragmenting. It also comes with a httpflow tool to extract HTTP requests and responses (including decompression, chunked encoding..). It does not currently handle SSL.
As the author of this library I don't think that extracting TCP flows is the hardest part, the HTTP parser (exluding decompression, including chunked mode) is nearly twice as big than IP and TCP combined.
This example works for reassembling application data of a single protocol:
tshark -Y "tcp.dstport == 80" -T fields -d tcp.port==80,echo -e echo.data
It captures live http data, reassembles it, and outputs it as raw hex.
I can add a small script to parse the hex into ascii if you like.
I want to analyse the SSL content in the case I have the server private key
TL;DR: This can't be done with a capturing tool alone.
Why not: Because each SSL session generates a new secret conversation key, and you can't decrypt the session without this key. Having the private server key is not enough. The idea behind this is that if someone captures your SSL traffic, saves it, and then a year later he "finds" the private server key, then he still won't be able to decrypt your traffic.
Related
I need to send a file to an HTTP server with the curl utility. However, as my server application only needs to process a single file, I'd like to avoid using some large HTTP framework with a wide range of functionality, so I'd like to stick to TCP/UDP protocols with some simple HTTP parser.
A file to send to the server may be quite large and I doubt if it is reasonable to send this file as a single TCP packet, so I'm dreaming of splitting this file into UDP packets and sending them one by one. But on the client side, all this must be done with a simple curl command, like curl --data-binary #filename 127.0.0.1:80.
Is it possible to split this request into several packets using WinSock API? For example, the server reads the name of a file, detects its size, allocates as many packets as needed and starts receiving UDP packets. Or maybe should I look at other ways of solving it?
I have FreeBSD host (some sort of HTTP Proxy) with spikes of retransmitted packets number. Is there any way to track were host loosing them (per incoming connection).
I usually capture a bunch of them with tcpdump or similar; and then post process them elsewhere. In your case that should not be hard - as you just need the header.
Something like tcpdump (without; or a < 200 byte -s fly) would do on the target machine.
Compress/move this file then off to a desktop machine to work on it. I'd start with something like wireshark (simply use the filters).
Beyond that - simple grep-ing/wc-counting or a small perl script may be called for. To save you re-inventing histograms; consider http://snippets.aktagon.com/snippets/62-How-to-generate-a-histogram-with-Perl or do a quick google.
Wireshark doesn't seem to be able to change the content of filtered packets in real time.
Does anyone know a symilar software which can change packet content that is filtered.
Finding something like this will really be a life saver
Thanks.
At least on Unices and -like where raw sockets are used, this is not possible, since the packet is copied to userspace and you only work on that copy. Furthermore, sending a packet back through the raw socket may be considered an "outgoing" packet so that it is, in fact, not reinjected to the input path where it should be. Raw sockets were — according to the Linux manpage — designed to implement new protocols, IOW, raw sockets are an "endpoint", not a "passthrough station".
For packet modification in the input path (passthrough-like), each OS has its own set of interfaces. In Linux (you were sort of unspecific as to which you target), that would be the nfqueue mechanism, usable through libnetfilter_queue. And of course, that is how wireshark, if it wanted to (I don't see it doing packet alteration last time I checked), would go about doing this.
Please give Burp Suite a try. It includes a repeater that let's you modify HTTP requests.
No wireshark won't let you change the contents of the packets and place them back on the line. However there are ways to change packets as they pass through the machine. Typically the host is setup with two nics bridged together. One nic is connected to one network and the other nic to the other network. Then as packets pass through this point the host can see them. Now you can use iptables/netfilter and write a module that changes data in the packet. For example you can write something that can remap source ip addresses. It's been a while since I've used netfilter/iptables, so I can't provide anymore details, but I have used it in a previous job to do some neat things with packets while they were inflight. It does mean you need a host machine sitting at network junction points though.
The documentation suggests that node.get("nextSibling") and node.get("previousSibling") are what you need.
Yes, it can.
You need to pass this option to the configure script before you build it:
--enable-packet-editor
when I type wget http://yahoo.com:80 on unix shell. Can some one explain me what exactly happens from entering the command to reaching the yahoo server. Thank you very much in advance.
RFC provide you with all the details you need and are not tied to a tool or OS.
Wget uses in your case HTTP, which bases on TCP, which in turn uses IP, then it depends on what you use, most of the time you will encounter Ethernet frames.
In order to understand what happens, I urge you to install Wireshark and have a look at the dissected frames, you will get an overview of what data belongs to which network layer. That is the most easy way to visualize and learn what happens. Beside this if you really like (irony) funny documents (/irony) have a look at the corresponding RFCs HTTP: 2616 for example, for the others have a look at the external links at the bottom of the wikipedia articles.
The program uses DNS to resolve the host name to an IP. The classic API call is gethostbyname although newer programs should use getaddrinfo to be IPv6 compatible.
Since you specify the port, the program can skip looking up the default port for http. But if you hadn't, it would try a getservbyname to look up the default port (then again, wget may just embed port 80).
The program uses the network API to connect to the remote host. This is done with socket and connect
The program writes an http request to the connection with a call to write
The program reads the http response with one or more calls to read.
I have some software which runs as a black box, I have no access to it. This software makes HTTP requests. What I want to do is intercept these requests, forward them on, catch the response, do something with it, before passing the response back to the software.
Can this be done? What's the best method?
Thanks
Edit: Requests are to the public internet from a local intranet via a gateway/router. I have root access to my machine. Another machine could be used as intermediate gateway.
Edit 2: Requests are not encrypted. What I am actually trying to do is save down any images that are requested.
Try yellosoft-alchemy.
If the communication isn't encrypted, use Ethereal (or any other similar program) to sniff the communication on the wire.
edit: since the communication isn't encrypted, you can do that easily with Ethereal. You can save each TCP stream independently from there.
Edit2: Ok, you want to do this automatically. In this case, I would suggest you look at two tools available on Linux called tcpflow and tcpreen.
tcpreen creates a proxy similar to what you want between a local port and a remote one. It's a TCP proxy, not an HTTP proxy so this means you'll have to write some parsing tool to isolate the HTTP streams that contain the images you want (probably based on the MIME type of the response). it's not too complex a task, though, if you understand how HTTP works.
tcpflow is similar to tcpreen except that it's a sniffer instead of a proxy. Use whatever tool you think its more adapted to your environment.