Packetman

Advanced tcpdump and Wireshark filter string generator.

Packetman is a packet capture filter generator modeled after Wireshark's String-Matching Capture Filter Generator but with a lot more features allowing much finer control over the packets you see.

Features:

String-matching (just like Wireshark's tool)
bit-string matching
hex-string matching
easy masking through ? wildcard characters
offsets in bits or bytes
use header field name instead of manual offsets
application specific queries
built-in header reference tables

Installation

Add this line to your application's Gemfile:

gem 'packetman'

And then execute:

$ bundle

Or install it yourself as:

$ gem install packetman

Usage

$ packetman -h

Usage: packetman [OPTIONS] FILTER_STRING
    -p, --protocol PROTO             Transport Protocol (tcp,udp,icmp)
    -t, --transport                  OFFSET starts at transport header instead of data payload
    -r, --radix RADIX                Treat FILTER_STRING as RADIX instead of String
    -o, --offset OFFSET              Offset in bits
    -b, --byte-offset                Use 8-bit bytes instead of bits for offset
    -w, --wildcard [CHARACTER=?]     Treat CHARACTER as single-character wildcard
    -v, --version                    Show version

Create and use a filter string to capture all HTTP GET requests to /foo/bar

$ sudo tcpdump -nA `packetman GET /foo/bar`
tcpdump: data link type PKTAP
tcpdump: verbose output suppressed, use -v or -vv for full protocol decode
listening on pktap, link-type PKTAP (Packet Tap), capture size 262144 bytes
16:49:04.516409 IP 127.0.0.1.54662 > 127.0.0.1.80: Flags [P.], seq 1488105913:1488105994, ack 1397163988, win 4121, options [nop,nop,TS val 875380202 ecr 2751916352], length 81: HTTP: GET /foo/bar HTTP/1.1
.....b....j...E.....@.@..S..
..:.....PX...SG......75.....
4-=....@GET /foo/bar HTTP/1.1
Host: localhost
User-Agent: curl/7.43.0
Accept: */*

Hexadecimal string with wildcards

$ packetman -r 16 -w '?' "A8C401???C200A"
tcp[((tcp[12:1] & 0xf0) >> 2) + 0:4] & 0xffffff00 = 0xa8c40100 && tcp[((tcp[12:1] & 0xf0) >> 2) + 4:2] & 0x0fff = 0x0c20 && tcp[((tcp[12:1] & 0xf0) >> 2) + 6:1] & 0xff = 0x0a

Base 4 string with wildcards and offset beginning at start of the TCP header

$ packetman -t -o 3 -r 4 -w i 1223iiii2212
tcp[0:4] & 0x1fe01fe0 = 0x0d6014c0

Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake rspec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/jescholl/packetman.

License

The gem is available as open source under the terms of the MIT License.