Dshell

An extensible network forensic analysis framework. Enables rapid development of plugins to support the dissection of network packet captures.

Key features:

• Deep packet analysis using specialized plugins
• Robust stream reassembly
• IPv4 and IPv6 support
• Multiple user-selectable output formats and the ability to create custom output handlers
• Chainable plugins
• Parallel processing option to divide the handling of data source into separate Python processes
• Enables development of external plugin packs to share and install new externally developed plugins without overlapping the core Dshell plugin directories

[!WARNING] The current 3.2.4 version of Dshell fixes several vulnerabilities including an out-of-memory exception that can crash a Dshell process. Users are encouraged to update to this version.

Guides

• Dshell User Guide
  • A guide to installation as well as both basic and advanced analysis with examples
  • Helps new and experienced end users with using and understanding the decoder-shell (Dshell) framework
• Dshell Developer Guide
  • A guide to plugin development with basic examples, as well as core function and class definitions, and an overview of data flow
  • Helps end users develop new, custom Dshell plugins as well as modify existing plugins

Requirements

• Linux (developed on Ubuntu 20.04 LTS)
• Python 3 (developed with Python 3.8.10)
• pypacker
• pcapy-ng
• pyOpenSSL
• geoip2
  • MaxMind GeoIP2 data sets
    • Used to map IP addresses to country codes
    • See Installation section for configuration

Optional

• oui.txt
  • used by some plugins that handle MAC addresses
  • place in <dshell>/data/
• elasticsearch
  • used in the elasticout output module
  • only necessary if planning to use elasticsearch to store output
• pyJA3
  • used in the tls plugin

Installation

1. Install Dshell with pip

• python3 -m pip install Dshell/ OR python3 -m pip install <Dshell-tarball>

1. Configure geoip2 by placing the MaxMind GeoLite2 data set files (GeoLite2-ASN.mmdb, GeoLite2-City.mmdb, GeoLite2-Country.mmdb) in [...]/site-packages/dshell/data/GeoIP/
2. Run dshell. This should drop you into a Dshell> prompt.

Basic Usage

• decode -l
  • This will list all available plugins, alongside basic information about them
• decode -h
  • Show generic command-line flags available to most plugins, such as the color blind friendly mode for all color output
• decode -p <plugin>
  • Display information about a plugin, including available command line flags
• decode -p <plugin> <pcap>
  • Run the selected plugin on a pcap or pcapng file
• decode -p <plugin1>+<plugin2> <pcap>
  • Chain two (or more) plugins together and run them on a pcap file
• decode -p <plugin> -i <interface>
  • Run the selected plugin live on an interface (may require superuser privileges)

Usage Examples

Showing DNS lookups in sample traffic

Dshell> decode -p dns ~/pcap/dns.cap | sort
[DNS] 2005-03-30 03:47:46    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 4146, TXT? google.com., TXT: b'\x0fv=spf1 ptr ?all' **
[DNS] 2005-03-30 03:47:50    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 63343, MX? google.com., MX: b'\x00(\x05smtp4\xc0\x0c', MX: b'\x00\n\x05smtp5\xc0\x0c', MX: b'\x00\n\x05smtp6\xc0\x0c', MX: b'\x00\n\x05smtp1\xc0\x0c', MX: b'\x00\n\x05smtp2\xc0\x0c', MX: b'\x00(\x05smtp3\xc0\x0c' **
[DNS] 2005-03-30 03:47:59    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 18849, LOC? google.com. **
[DNS] 2005-03-30 03:48:07    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 39867, PTR? 104.9.192.66.in-addr.arpa., PTR: 66-192-9-104.gen.twtelecom.net. **
[DNS] 2005-03-30 03:49:18    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 30144, A? www.netbsd.org., A: 204.152.190.12 (ttl 82159s) **
[DNS] 2005-03-30 03:49:35    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 61652, AAAA? www.netbsd.org., AAAA: 2001:4f8:4:7:2e0:81ff:fe52:9a6b (ttl 86400s) **
[DNS] 2005-03-30 03:50:35    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 32569, AAAA? www.netbsd.org., AAAA: 2001:4f8:4:7:2e0:81ff:fe52:9a6b (ttl 86340s) **
[DNS] 2005-03-30 03:50:44    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 36275, AAAA? www.google.com., CNAME: 'www.l.google.com.' **
[DNS] 2005-03-30 03:50:54    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 56482, AAAA? www.l.google.com. **
[DNS] 2005-03-30 03:51:35    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 48159, AAAA? www.example.com. **
[DNS] 2005-03-30 03:51:46    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 9837, AAAA? www.example.notginh., NXDOMAIN **
[DNS] 2005-03-30 03:52:17    192.168.170.8:32795 --   192.168.170.20:53    ** ID: 65251, AAAA: 2001:4f8:0:2::d (ttl 600s), A: 204.152.184.88 (ttl 600s) **
[DNS] 2005-03-30 03:52:17    192.168.170.8:32796 --   192.168.170.20:53    ** ID: 23123, PTR? 1.0.0.127.in-addr.arpa., PTR: localhost. **
[DNS] 2005-03-30 03:52:17    192.168.170.8:32797 --   192.168.170.20:53    ** ID: 8330, NS: b'\x06ns-ext\x04nrt1\xc0\x0c', NS: b'\x06ns-ext\x04sth1\xc0\x0c', NS: b'\x06ns-ext\xc0\x0c', NS: b'\x06ns-ext\x04lga1\xc0\x0c' **
[DNS] 2005-03-30 03:52:17   192.168.170.56:1707  --      217.13.4.24:53    ** ID: 12910, SRV? _ldap._tcp.Default-First-Site-Name._sites.dc._msdcs.utelsystems.local., NXDOMAIN **
[DNS] 2005-03-30 03:52:17   192.168.170.56:1708  --      217.13.4.24:53    ** ID: 61793, SRV? _ldap._tcp.dc._msdcs.utelsystems.local., NXDOMAIN **
[DNS] 2005-03-30 03:52:17   192.168.170.56:1709  --      217.13.4.24:53    ** ID: 33633, SRV? _ldap._tcp.05b5292b-34b8-4fb7-85a3-8beef5fd2069.domains._msdcs.utelsystems.local., NXDOMAIN **
[DNS] 2005-03-30 03:52:17   192.168.170.56:1710  --      217.13.4.24:53    ** ID: 53344, A? GRIMM.utelsystems.local., NXDOMAIN **
[DNS] 2005-03-30 03:52:25   192.168.170.56:1711  --      217.13.4.24:53    ** ID: 30307, A? GRIMM.utelsystems.local., NXDOMAIN **

Following and reassembling a stream in sample traffic

Dshell> decode -p followstream ~/pcap/v6-http.cap 
Connection 1 (TCP)
Start: 2007-08-05 15:16:44.189851
End:   2007-08-05 15:16:44.219460
2001:6f8:102d:0:2d0:9ff:fee3:e8de: 59201 -> 2001:6f8:900:7c0::2:    80 (300 bytes)
2001:6f8:900:7c0::2:    80 -> 2001:6f8:102d:0:2d0:9ff:fee3:e8de: 59201 (2379 bytes)

GET / HTTP/1.0
Host: cl-1985.ham-01.de.sixxs.net
Accept: text/html, text/plain, text/css, text/sgml, */*;q=0.01
Accept-Encoding: gzip, bzip2
Accept-Language: en
User-Agent: Lynx/2.8.6rel.2 libwww-FM/2.14 SSL-MM/1.4.1 OpenSSL/0.9.8b



HTTP/1.1 200 OK
Date: Sun, 05 Aug 2007 19:16:44 GMT
Server: Apache
Content-Length: 2121
Connection: close
Content-Type: text/html

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 3.2 Final//EN">
<html>
 <head>
  <title>Index of /</title>
 </head>
 <body>
<h1>Index of /</h1>
<pre><img src="/icons/blank.gif" alt="Icon "> <a href="?C=N;O=D">Name</a>                    <a href="?C=M;O=A">Last modified</a>      <a href="?C=S;O=A">Size</a>  <a href="?C=D;O=A">Description</a><hr><img src="/icons/folder.gif" alt="[DIR]"> <a href="202-vorbereitung/">202-vorbereitung/</a>       06-Jul-2007 14:31    -   
<img src="/icons/layout.gif" alt="[   ]"> <a href="Efficient_Video_on_demand_over_Multicast.pdf">Efficient_Video_on_d..&gt;</a> 19-Dec-2006 03:17  291K  
<img src="/icons/unknown.gif" alt="[   ]"> <a href="Welcome%20Stranger!!!">Welcome Stranger!!!</a>     28-Dec-2006 03:46    0   
<img src="/icons/text.gif" alt="[TXT]"> <a href="barschel.htm">barschel.htm</a>            31-Jul-2007 02:21   44K  
<img src="/icons/folder.gif" alt="[DIR]"> <a href="bnd/">bnd/</a>                    30-Dec-2006 08:59    -   
<img src="/icons/folder.gif" alt="[DIR]"> <a href="cia/">cia/</a>                    28-Jun-2007 00:04    -   
<img src="/icons/layout.gif" alt="[   ]"> <a href="cisco_ccna_640-801_command_reference_guide.pdf">cisco_ccna_640-801_c..&gt;</a> 28-Dec-2006 03:48  236K  
<img src="/icons/folder.gif" alt="[DIR]"> <a href="doc/">doc/</a>                    19-Sep-2006 01:43    -   
<img src="/icons/folder.gif" alt="[DIR]"> <a href="freenetproto/">freenetproto/</a>           06-Dec-2006 09:00    -   
<img src="/icons/folder.gif" alt="[DIR]"> <a href="korrupt/">korrupt/</a>                03-Jul-2007 11:57    -   
<img src="/icons/folder.gif" alt="[DIR]"> <a href="mp3_technosets/">mp3_technosets/</a>         04-Jul-2007 08:56    -   
<img src="/icons/text.gif" alt="[TXT]"> <a href="neues_von_rainald_goetz.htm">neues_von_rainald_go..&gt;</a> 21-Mar-2007 23:27   31K  
<img src="/icons/text.gif" alt="[TXT]"> <a href="neues_von_rainald_goetz0.htm">neues_von_rainald_go..&gt;</a> 21-Mar-2007 23:29   36K  
<img src="/icons/layout.gif" alt="[   ]"> <a href="pruef.pdf">pruef.pdf</a>               28-Dec-2006 07:48   88K  
<hr></pre>
</body></html>

Chaining plugins to view flow data for a specific country code in sample traffic (note: TCP handshakes are not included in the packet count)

Dshell> decode -p country+netflow --country_code=JP ~/pcap/SkypeIRC.cap
2006-08-25 15:32:20.766761       192.168.1.2 ->  202.232.205.123  (-- -> JP)   UDP   60583   33438     1      0       64        0  0.0000s
2006-08-25 15:32:20.634046       192.168.1.2 ->  202.232.205.123  (-- -> JP)   UDP   60583   33435     1      0       64        0  0.0000s
2006-08-25 15:32:20.747503       192.168.1.2 ->  202.232.205.123  (-- -> JP)   UDP   60583   33437     1      0       64        0  0.0000s
2006-08-25 15:32:20.651501       192.168.1.2 ->  202.232.205.123  (-- -> JP)   UDP   60583   33436     1      0       64        0  0.0000s

Collecting DNS traffic from several files and storing it in a new pcap file.

Dshell> decode -p dns+pcapwriter --pcapwriter_outfile=test.pcap ~/pcap/*.cap > /dev/null
Dshell> tcpdump -nnr test.pcap | head
reading from file test.pcap, link-type EN10MB (Ethernet)
15:36:08.670569 IP 192.168.1.2.2131 > 192.168.1.1.53: 40209+ A? ui.skype.com. (30)
15:36:08.670687 IP 192.168.1.2.2131 > 192.168.1.1.53: 40210+ AAAA? ui.skype.com. (30)
15:36:08.674022 IP 192.168.1.1.53 > 192.168.1.2.2131: 40209- 1/0/0 A 212.72.49.131 (46)
15:36:09.011208 IP 192.168.1.1.53 > 192.168.1.2.2131: 40210 0/1/0 (94)
15:36:10.171350 IP 192.168.1.2.2131 > 192.168.1.1.53: 40210+ AAAA? ui.skype.com. (30)
15:36:10.961350 IP 192.168.1.1.53 > 192.168.1.2.2131: 40210* 0/1/0 (85)
15:36:10.961608 IP 192.168.1.2.2131 > 192.168.1.1.53: 40211+ AAAA? ui.skype.com. (30)
15:36:11.294333 IP 192.168.1.1.53 > 192.168.1.2.2131: 40211 0/1/0 (94)
15:32:21.664798 IP 192.168.1.2.2130 > 192.168.1.1.53: 39862+ A? ui.skype.com. (30)
15:32:21.664913 IP 192.168.1.2.2130 > 192.168.1.1.53: 39863+ AAAA? ui.skype.com. (30)

Collecting TFTP data and converting alerts to JSON format using sample traffic

Dshell> decode -p tftp -O jsonout ~/pcap/tftp_*.pcap
{"ts": 1367411051.972852, "sip": "192.168.0.253", "sport": 50618, "dip": "192.168.0.10", "dport": 3445, "readwrite": "read", "filename": "rfc1350.txt", "plugin": "tftp", "pcapfile": "/home/pcap/tftp_rrq.pcap", "data": "read  rfc1350.txt (24599 bytes) "}
{"ts": 1367053679.45274, "sip": "192.168.0.1", "sport": 57509, "dip": "192.168.0.13", "dport": 2087, "readwrite": "write", "filename": "rfc1350.txt", "plugin": "tftp", "pcapfile": "/home/pcap/tftp_wrq.pcap", "data": "write rfc1350.txt (24599 bytes) "}

Running a plugin within a separate Python script using sample traffic

# Import required Dshell libraries
import dshell.decode as decode
import dshell.plugins.tftp.tftp as tftp

# Instantiate plugin
plugin = tftp.DshellPlugin()
# Define plugin-specific arguments, if needed
dargs = {plugin: {"rip": True, "outdir": "/tmp/"}}
# Add plugin(s) to plugin chain
decode.plugin_chain = [plugin]
# Run decode main function with all other arguments
decode.main(
    debug=True,
    files=["/home/user/pcap/tftp_rrq.pcap", "/home/user/pcap/tftp_wrq.pcap"],
    plugin_args=dargs
)