NETRESEC Network Security Blog - Tag : DFRWS

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Carving Packets from Memory

The packets are in the router

Someone who says "We're gonna pull the packet captures out of the router" probably has no clue how to capture network traffic. In the Lindell case, statements like these were results of an elaborate hoax.

Nevertheless, such a statement doesn't have to be nonsense — if it comes from someone who knows how to dump the physical memory from the router. There are actually more packets available in the RAM of a router, or computer for that matter, than you might think.

The Forensic Challenge from DFRWS 2016 contains a memory dump from an SDN switch. If you drag-and-drop SDN.ram.raw from that challenge to CapLoader then you'll be asked if you wanna carve packets from the memory dump.

CapLoader error message - Invalid capture file

This packet carving feature is also available in the free trial version of CapLoader.

Clicking "Yes" in the dialogue brings up a configuration window. The default settings are okay in most cases.

CapLoader's Carve Packets Window

After pressing "Start" CapLoader will start identifying packets in the memory dump from the SDN switch. The packets will be saved to a Pcap-NG file located in the %TEMP% directory, unless you specified a different output location in the config window.

You can download a copy of the Pcap-NG file that I generated with CapLoader 1.9.2 here: https://www.netresec.com/files/SDN.ram.raw.pcapng (661 kB, 2959 packets)

Here's what it looks like when the carved packets have been loaded into NetworkMiner Professional.

NetworkMiner Professional with SDN.ram.raw.pcapng loaded

As you can see, a great deal of information can be extracted about the hosts on this network just by examining the dumped memory from the SDN switch.

What about Bulk Extractor?

Simson Garfinkel's bulk_extractor can also extract packets from memory dumps. It was actually a research paper by Simson that inspired me to implement a packet carver in the first place.

There are a few significant differences between bulk_extractor and CapLoader with regards to packet carving though. One difference is that bulk_extractor identifies network packets by looking for Ethernet frames containing IPv4 packets, while CapLoader looks for IPv4 or IPv6 packets containing TCP or UDP packets. The output from bulk_extractor is usually quite similar to that of CapLoader, and so is the parsing speed. CapLoader was just slightly faster in our tests and carved about 3% more packets compared to bulk_extractor, these additional packets were primarily IPv6 packets and packets that weren't encapsulated by an Ethernet frame.

Where can I download memory dumps?

I posted a question on Twitter, asking the #DFIR community for their favorite publicly available memory dumps prior to writing this blog post, and I received lots of great answers. Thank you all for contributing! I have now compiled the following list of places from where you can download memory dumps:

For a more detailed blog post on CapLoader's packet carving functionality, please see our Carving Network Packets from Memory Dump Files blog post from 2014.

Posted by Erik Hjelmvik on Tuesday, 31 August 2021 15:10:00 (UTC/GMT)

Tags: #Forensics #RAM #PCAP #Pcap-NG #PcapNG #DFIR #carve #carver #packets #dump #CapLoader #memory forensics #DFRWS

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Recommended Books

» The Practice of Network Security Monitoring, Richard Bejtlich (2013)

» Applied Network Security Monitoring, Chris Sanders and Jason Smith (2013)

» Network Forensics, Sherri Davidoff and Jonathan Ham (2012)

» The Tao of Network Security Monitoring, Richard Bejtlich (2004)

» Practical Packet Analysis, Chris Sanders (2017)

» Windows Forensic Analysis, Harlan Carvey (2009)

» TCP/IP Illustrated, Volume 1, Kevin Fall and Richard Stevens (2011)

» Industrial Network Security, Eric D. Knapp and Joel Langill (2014)