Examining the art of computer forensics
Connection Origin
One final thing that forensic investigators should not forget is that the origin of a TCP or UDP connection does not necessarily match the attacker's location. Some attackers use hijacked systems as a starting point for their work.
If the connection originates with a system that is very close to your own network, you should be extremely cautious. A short list of hops in the output from tcpdump target-address will tell you more. If you can rule out a regular user, you have fairly convincing evidence that an attacker has made inroads into your network. An attacker who is close is much more dangerous than one who is far away. (Sniffing passwords off the same subnet is much easier than off the Internet.)
Looking for Clues
If the forensics expert has discovered an unknown process or program running on the system, the next question is: "What does the malware actually do?"
Is it just a jumping-off point for more attacks? If so, an unknown process will probably have created an entry in the socket list.
Does it sniff data off the network? If so, look for a network interface in promiscuous mode.
Typically, this creates an audit entry in the kernel ring buffer, and you can run dmesg to find out:
device eth0 entered promiscuous mode audit(1408381411.504:2): dev=eth0 prom=256 old_prom=0 auid=4267295 device eth0 left promiscuous mode audit(1408381413.144:3): dev=eth0 prom=0 old_prom=256 auid=4297295
What are you supposed to do if you see an active process but don't know what it does? To start, it makes sense to start by backing up the process itself. To locate the executable, type ps gauxwww or check /proc/PID/cmdline.
What are you supposed to do if an attacker has launched a tool, immediately deleted it, and overwritten the disk sectors? While the program is running, there is hope – the kernel keeps a virtual symlink to the executable in /proc/PID/exe, even if the attacker has deleted it from the filesystem. If the response team saves this file somewhere safe, analysis is often possible at a later stage.
Poking in the Binary Trash
One simple but effective approach is to take a closer look at the binary itself. The strings -a binary command searches a file for printable characters. If the malware connects to an FTP or web server that requires a password, you might be able to find the password in the program code. But you will need a modicum of intuition to distinguish digital bread crumbs from binary trash.
« Previous 1 2 3 Next »
Buy this article as PDF
(incl. VAT)
Buy Linux Magazine
Subscribe to our Linux Newsletters
Find Linux and Open Source Jobs
Subscribe to our ADMIN Newsletters
Support Our Work
Linux Magazine content is made possible with support from readers like you. Please consider contributing when you’ve found an article to be beneficial.
News
-
OSJH-LPI Release 2024 Open Source Pros Job Survey Results
See what open source professionals look for in a new role.
-
Proton 9.0-1 Released to Improve Gaming with Steam
The latest release of Proton 9 adds several improvements and fixes an issue that has been problematic for Linux users.
-
So Long Neofetch and Thanks for the Info
Today is a day that every Linux user who enjoys bragging about their system(s) will mourn, as Neofetch has come to an end.
-
Ubuntu 24.04 Comes with a “Flaw"
If you're thinking you might want to upgrade from your current Ubuntu release to the latest, there's something you might want to consider before doing so.
-
Canonical Releases Ubuntu 24.04
After a brief pause because of the XZ vulnerability, Ubuntu 24.04 is now available for install.
-
Linux Servers Targeted by Akira Ransomware
A group of bad actors who have already extorted $42 million have their sights set on the Linux platform.
-
TUXEDO Computers Unveils Linux Laptop Featuring AMD Ryzen CPU
This latest release is the first laptop to include the new CPU from Ryzen and Linux preinstalled.
-
XZ Gets the All-Clear
The back door xz vulnerability has been officially reverted for Fedora 40 and versions 38 and 39 were never affected.
-
Canonical Collaborates with Qualcomm on New Venture
This new joint effort is geared toward bringing Ubuntu and Ubuntu Core to Qualcomm-powered devices.
-
Kodi 21.0 Open-Source Entertainment Hub Released
After a year of development, the award-winning Kodi cross-platform, media center software is now available with many new additions and improvements.