I.T. Security and Linux Administration

January 16, 2013  11:14 AM

Getting Into Linux Security (Part 1)

Eric Hansen Eric Hansen Profile: Eric Hansen

There’s a big increase lately in terms of Linux security and how to get into the field.  Some can get by only knowing basic command line arguments, others require a CISSP to even be considered.  But, experience in the field itself shows more than anything, even if you’re sitting at your desk working through a virtual machine.  But what can really help someone, who’s passionate about security and Linux become even better?  Help them get a job, and even start their own Linux security business?

Test Environments

You’re not going to know the tricks and ropes of every situation. Even if you were to simulate your own DoS and see how it affects your home network, there’s many ways to construct such an attack.

What you can do, however, is set up a virtual environment, or even a small virtual server farm. Get them to talk to each other, throw DoS attacks at them and see how they react. Having the knowledge of virtualization will get you further ahead than you may think, especially if you work for a “go green” company.

Scenario: I had a job interview late last year for a company. I did pretty well up until troubleshooting came into play. Safe to say I didn’t get the job, but knowing what they were looking for me to do on a day-to-day basis really opened my eyes. It made me realize what I need to focus more on, and how to do so. I ended up taking that knowledge, installing a small Linux distro on a server and trying to simulate various issues. With virtualization I can kill the network adapter without interrupting anything important. I’m able to run through various scenarios in practice that I was tested with in the interview, and try to solve them there.

It’s not a permanent solution, but it helps a lot. Heck, I have another scenario for you.

Scenario: Working for a web hosting company, I was placed in the position of rebuilding a RAID array. I had very minimal experience with such technology and only knew a little bit of the basics. But, I was forced to dive in blindfolded and do it what I needed to do. I don’t remember the details, but I can definitely tell you it didn’t go well (I told them before hand I wasn’t sure what I was doing, but I sure learned what not to do hah). Anyways, after I got off work, I went back to my place, and again installed a server via virtual machine. I spent a good week toying with RAID and how to work with it. Even to this day I’ve done it, and have also written various scripts to make the process smoother.

Virtualization is probably going to be your biggest friend going into security. There’s so many things that can break and go wrong that it’s easier being to reformat a virtual machine than it is reformatting your PC.

Knowing the Software (Part 1)


This here is going to be at least a two-part coverage, because in security there is just too much to cover. However, the biggest tool I see in the arsenal everywhere is nmap. Especially if you’re looking to set up or test a firewall, nmap should always be the first tool you go to. It will help you test against malformed packets, scan the network for devices and a whole lot more. The documentation on this tool will pretty much speak more volume than I can about it, but you should definitely learn your way around this piece of software.

Scenario: You notice a lot of traffic being sent to a server but no requests being fullfilled. this can either be an attempted DoS attack or someone just sending bad packets. The best way to find out if you don’t have network monitoring software set up is to test. While nmap won’t be a viable solution to test for a DoS attack, it does provide a vast array of methods to test for bad packets. You can run the host against each known test in nmap, and compare the results until you find a match.

December 31, 2012  3:51 PM

Privacy Policy and Big Brother

Eric Hansen Eric Hansen Profile: Eric Hansen

Recently there’s been a lot of hysteria about privacy and the controls to it. A good instance of this is Facebook, which has essentially been under the gun ever since (or even before) it’s IPO failure earlier this year.

The idea behind privacy policies are nice, but short of being something to sue a company over, they hold very little information. They don’t tell you how the data stored or distributed, just that they are. It doesn’t say what happens on a privacy breach, or how to protect your data. It also doesn’t provide information on how to protect your privacy, just that it’s possible.

A lot of businesses, especially social media-based ones, are primarily focused on bringing in users, but they tend to give the assumption all of their users are computer-conscious. In fact, the safest way to present this to the user should be to assume that their users are not savvy and to spell out the information instead.

December 31, 2012  3:28 PM

Review: Snort GUI – Snorby

Eric Hansen Eric Hansen Profile: Eric Hansen

Typical Snort installs have you installing BASE for a graphical front-end to view packet information. While the UI is fluid, it’s also very outdated. It has the coding standards of 1995-2000, with limited functionality in it (just enough to get what you want and get out).

As such, there’s been advances in making viewing Snort logs easier. Of those is Snorby (www.snorby.org). It’s based on Ruby on Rails and has a pretty slick interface that brings Web 2.0 to Snort. But how good is it, really?

Personally I can’t stand any RoR projects. They’re about as resource intensive as Java programs and have about the same performance. It’s great if you have a 32-CPU and 192GB RAM server, but if you’re trying to operate it on a VPS, you’ll need a pretty high-end VPS just to give it enough RAM (Xen VPS might be better suited).

The UI is nice but it feels a bit clunky in that it tries to present too much to you at once. Otherwise, the color scheme is nice, but the navigation feels like everything is just clumped up together.

December 31, 2012  2:45 PM

Shell Portscanner

Eric Hansen Eric Hansen Profile: Eric Hansen

Many, many people have heard of nmap before. The infamous port scanner that does everything you can think of. This is great if you’re wanting to do recon on a network, but what if you just want to see what ports are open on a network without all the extra special features? Easy, you use Bash!

Below is a simple Bash script that uses the system’s TCP “device” to establish the connection and see if the port is open or closed:
# Code is swipped from http://legroom.net/2010/05/02/port-testing-and-scanning-bash
# Usage: ./portscan.sh
# Change range in {...} block as you please.

function port() {
(echo > /dev/tcp/$1/$2) &> /dev/null
if [ $? -eq 0 ]; then
echo "$1:$2 open"
echo "$1:$2 closed"

for i in {22..80}; do
port $1 $i

This does a check for ports 22-80, but you can change the range to match your needs. A link to this can be found here: https://gist.github.com/4422216

December 31, 2012  2:24 PM

IPv6 Startup Script

Eric Hansen Eric Hansen Profile: Eric Hansen

After writing this article: https://itknowledgeexchange.techtarget.com/security-admin/ipv6-and-linux/ I decided to write a simple script that will allow you to start and stop the IPv6 functionality pretty easily. The script is pretty well commented and easy to use:


# This script is modified from the one found here: https://wiki.archlinux.org/index.php/IPv6_-_Tunnel_Broker_Setup
# Noticably this script now runs like this:
# $0
# So if you want IPv6 traffic to be routed through wlan0, you would do:
# $0 start wlan0

if [ "$EUID" -ne 0 ]; then
echo "You must run this as root"
exit 1

# Edit these
server_ipv4='' # HE Server Endpoint IP
client_ipv6='' # Your HE-assigned client IP

# Don't edit below this line

if [ -n "$2" ]; then
client_ipv4=$(ifconfig eth0 | grep netmask | awk '{print $2}')

if [ -z "$client_ipv4" ]; then
echo "Usage: $0 "
exit 1

echo "Tunneling data from IPv6 to $2 (IP: $client_ipv4)"


# . /etc/rc.conf
# . /etc/rc.d/functions

case "$1" in
# stat_busy "Starting $daemon_name daemon"

ifconfig $if_name &>/dev/null
if [ $? -eq 0 ]; then
stat_busy "Interface $if_name already exists"
exit 1

ip tunnel add $if_name mode sit remote $server_ipv4 local $client_ipv4 ttl $tunnel_ttl
ip link set $if_name up mtu $link_mtu
ip addr add $client_ipv6 dev $if_name
ip route add ::/0 dev $if_name
# Here is how you would add additional ips....which should be on the eth0 interface
# ip addr add 2001:XXXX:XXXX:beef:beef:beef:beef:1/64 dev eth0
# ip addr add 2001:XXXX:XXXX:beef:beef:beef:beef:2/64 dev eth0
# ip addr add 2001:XXXX:XXXX:beef:beef:beef:beef:3/64 dev eth0

add_daemon $daemon_name

stat_busy "Stopping $daemon_name daemon"

ifconfig $if_name &>/dev/null
if [ $? -ne 0 ]; then
stat_busy "Interface $if_name does not exist"
exit 1

ip link set $if_name down
ip tunnel del $if_name

rm_daemon $daemon_name

echo "usage: $0 {start|stop}"
exit 0

The download link for this script can be found here: https://gist.github.com/4422119

December 31, 2012  2:11 PM

IPv6 and Linux

Eric Hansen Eric Hansen Profile: Eric Hansen

IPv6 isn’t a new thing, nor is it really a wave of the future at this point. It’s been in development since the late 90’s when the inherent flaw of IPv4 was finally considered important. However, over the last few years it has made great strides in trying to take over it’s older brother. But, even to this day, while you’re assigned an IPv6 address, it doesn’t necessarily mean you can reach out to the IPv6-accessible websites. A good way to test this is by trying to go to http://ipv6.google.com. If it works, you’ll be welcomed to the standard Google search page. If it doesn’t, you’ll typically see a DNS lookup-related error. This is because IPv6 is not accessible via IPv4.

Recently I took up the position of trying to get IPv6 to play nicely with my home network. I don’t use anything fancy, and ultimately this costed me a grand total of $0.00. But, there are endless possibilities once you do this.

First, I’m going to assume you have Linux installed and you know how to use your distro’s repos. We will be installing some software. I’m using Arch Linux 64-bit, but I’m 99% certain the steps are similar for others out there as well. Just might need some tweaks here and there.

Now, what you need to do is install iproute2. If your system allows you to run this command: “ip addr” (without quotes) then you already have it installed. Wikipedia has a good enough article about iproute2 here: http://en.wikipedia.org/wiki/Iproute2

Once you have that installed, you will need to register for an IPv6 address. You’ll probably have one locally, but this is used externally. While there’s a few “tunnel brokers” out there that offer this functionality, I use Hurricane Electric’s http://tunnelbroker.net/. I have a VPS rented out from them too so I already knew their network was decent. This is simple to do, you just need to click on the “Register” button, fill out the information and submit it.

Now, from here you need to add a tunnel. This threw me off at first, so I’m going to assume you’re being a router here. Having a private IP address and everything. If not, then the step still applies.

Once you’re logged in, go to the “User Functions” section on the left side, and click on “Regular Tunnel”. From there, fill out the info. Now, it’s all pretty self-explanatory, but what threw me off at first was the “IPv4 Endpoint”. This is actually your network’s public-facing IP. So if your ISP gave you an IP of, you would put in there It’ll also suggest the closest DC to route you from based on your IP’s geographical location.

Once your tunnel is created, you’ll be faced with a tunnel info page. What you need to do is click on the “Example Configurations” page and choose your method (i.e.: Linux-route2). It’ll give you a list of commands to put into your shell (as root or via sudo). Once you do that, run ping6 -c 1 ipv6.google.com and you should be able to ping Google.

Note that while this allows you to have IPv6 availability, you can still browse IPv4 websites just fine.

December 14, 2012  12:06 PM

Snort on Low-End Servers

Eric Hansen Eric Hansen Profile: Eric Hansen

Recently I’ve been looking more in-depth into Snort.  I’ve had it in use for my business for a little while now, but I wanted to see how far down the spec-chain I can get it to run on.  I already had it running fine in a virtual machine environment with 4GB of RAM, so I worked from that machine.  While this proved to be quite interesting (who wouldn’t love to run a Snort sensor on a Raspberry Pi?), it also proved to be a little stressful.

The documentation on how to get Snort to run on low-spec’ed machines was for the most part out of date.  Most of them would say to add ‘low-mem’ to the ‘configuration detection’.  With Snort 2.9.3, I found this wasn’t exactly a working solution as I kept receiving the error that ‘low-mem’ is not a valid option.  Another thing I was to told to try is to change the search-method option to something like ‘lowmem-nq’, which in conjunction with what I found to be the answer is can help, but you still have to dig a little bit deeper.

What I found I had to tweak is actually the ‘max_*’ settings for the stream5_global preprocessor.  When I was trying to run Snort, I would always receive an error saying that the flowbits could not be allocated in stream5_global.c, which I dug for about an hour trying to figure out what was actually going on.  Since this I have also learned there’s a ‘config flowbits_size’ config option (commented out by default), but I did not want to mess with that as I’m not sure what it would do.

Instead, here’s what my preprocessor looks like on a 4GB virtual machine:

preprocessor stream5_global: track_tcp yes, track_udp yes, tracp_icmp no, max_tcp 262144, max_udp 131072, max_active_responses 2, min_response_seconds 5

Not having the preprocessor track packets you’re not interested in (i.e.: no icmp if you don’t care about those) will reduce the memory usage as well, but what you have to actually focus on is the max_* settings.  These tell the preprocessor how many sessions at a given time it can keep track of for each protocol, which in short terms also leads it to allocating enough memory to handle such a work load.  I disabled tracking icmp and udp as my server only permits TCP anyways, and reduced the max_tcp to a very small value of 1024 to see if it would run.  Low and behold, it ran without issues and I can monitor traffic just fine!

max_tcp has to be within the range of 1 and 1048576 (max_tcp, udp and icmp have different ranges).  If you set the value higher than what your VM can handle, you’ll receive an error similar to:

ERROR: snort_stream5_tcp.c(949) Could not initialize tcp session memory pool.
Fatal Error, Quitting..

As TCP likes to have everything in multiples of 32, I’m a fan of sticking with such multiples, but anywhere within the region mentioned earlier will be fine.  If you have 256MB of RAM, I’ve found that the highest setting (for me at least) that works is 9999 for max_tcp.  Which for a small network it should be just fine, if not overly abundant.

Also, please note that limiting the rules, preprocessors, etc… that are running will also reduce the memory footprint as well, so this is by no means a de-facto standard of how to get it to run, but it’s definitely a step in the newer right direction.

November 30, 2012  8:27 PM

To Release, or Not Release Full Disclosures?

Eric Hansen Eric Hansen Profile: Eric Hansen

Wired posted an interesting article this month discussing the benefits and losses of hackers releasing exploits out into the wild and to vendors.  Some of the points I agree with, but some I do not.

I do feel that exploits should be released to the vendors before disclosure.  Back in my hay-day of finding exploits, I had a set ruling:

  1. Find exploit
  2. Send any/all contacts for vendor an e-mail outlining the exploit
  3. Wait 7 days
  4. If no response, release exploit as live, otherwise publish it as is.  Both scenarios would be labelled as vendor-notified

This was simple: in the e-mail, I would provide the software name and version, OS if needed along with any other system specifics, what the exploit is, does and how to patch it.  I would also include a note saying that if no response is received within 7 days, the exploit will be released to the world.

My view was that it is up to the vendor at that point to either fix it, or not.  None of the exploits I found was extensive (i.e.: sifting through the code of Virtual Box to find out a memory leak happens when some action occurs).  It was mostly beginner stuff, such as local/remote file inclusion and cross-site scripting.  Some vendors responded back, most didn’t.  Out of those who did, I had a long-lasting relationship with one in fixing exploits for him.

I do not, however, condone the releasing of such information to the public without properly informing the vendor first, however (unless of course they cannot be reached).  I never classified myself as any type of hat, but if I had to it’d be grey.  I didn’t find exploits to ruin the lives of people, I found them because I love security.  I wanted to reach out to those who needed help, and do my best.  However, with-holding valuable information such as exploits for personal gain of any sort is far from beneficial to anyone, even yourself.  For every exploit you can find, there’s someone out there who can find more, and they may give away your exploit before you have the chance.

November 30, 2012  8:03 PM

Security Precuation In Programming: Validate User Input

Eric Hansen Eric Hansen Profile: Eric Hansen

When most people think of validating user input, the first thing to come to mind is making sure a string is a string, numbers are numbers and dates are proper.  But does it stop there?  Let’s have Facebook decide.

It seems there’s a new exploit available for their chat system, and it’s not something most people would ever cause due to the nature and extreme case of this scenario.  The overall action that you need to perform is to send an extremely long message via chat to Facebook’s servers, which will then crash the end user’s session (and yours).  This has further repercussions for Facebook apps that keep chat sessions alive (i.e.: tablet Facebook apps), as they will no longer be able to use the Facebook chat program on their tablet due to the fact the Messenger app would be constantly trying to load the too-long message, and crashing the app.  This was posted on seclists.org by Chris Russo (http://seclists.org/fulldisclosure/2012/Nov/46).

While it does have a specific use case, and is not something the average user would ever reach such limits needed to cause this issue, it also shows that proper data validation is far from properly implemented, even with big-name corporations.  If it’s as simple as sending a “malformed” request to Facebook’s chat service, how easy would it be to do the same with GTalk, IRC, etc…?

November 30, 2012  6:19 PM

Proper Firewall Management: Part 1 – Introduction To fail2ban

Eric Hansen Eric Hansen Profile: Eric Hansen

As a short series, I will be showcasing some firewall tips and tricks on what to (not) do if you want to secure your network.  The first of which is going to be an overview for a very helpful log analyzer, fail2ban.  There’s other programs out there, such as logwatch, that monitor logs and ensure nothing ‘illegal’ is occurring.  However, fail2ban is the most well known one that will also act on such findings.  To me, it is the IDS of logs.

fail2ban works based on configuration files that specify what program ID (i.e.: http, pop3) it’s parsing for, and then another file that specifies the rules that match restricted content.  This also makes fail2ban optimal for those looking to use your mail server for relaying, SSH for proxying or flooding your server with malformed HTTP requests.  Essentially all you do is throw in the rule(s) you want matched, and fail2ban will match the regex expression with data in logs.  If anything is found, it will then add the offending IP to iptables for a given period of time.

fail2ban is also useful for overseeing the network and handling of Snort logs to automatically restrict offending IPs without having to parse through each Snort log yourself.

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