Category Archives: Tools

Networking, Solved, Tools

Asterisk – Seamless dialing of remote extension through DTMF

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Problem Description:

There are two offices.  Office A runs Asterisk / FreePBX while office B runs a closed system with auto attendant.

The guys at office A would like to be able to dial office B extensions as if they were local.

 

Solution Overview:

Program the office A extensions in this way:

  1. Local extension picks up
  2. Remote office number is called
  3. When the remote office picks up
  4. DTMF key presses are sent to select the right extension
  5. Call is connected

Solution Details:

First I attempted to program this into freePBX through the GUI, but I wasn’t having any luck because the default macros were not letting me craft the dial command in such a way that it sends the key presses after the call is placed.   Although it would have been nice to have everything in the GUI, the FreePBX GUI method seems to be a dead end.  I ended up relying on good old /etc/asterisk/extensions_custom.conf configuration file, and I just created my own extensions there.

[ext-local]
exten => 102,1,Dial(SIP/v-outbound/4031112222,30,rD(ww11))
exten => 103,1,Dial(SIP/v-outbound/4032223333,30,rD(ww12))

[ext-local] sets the right context so that these extensions are picked up as if they were local.  You could also put these into other contexts like [ivr-1] etc.

D tells the Dial command to send DTMF button presses after the remote end picks up

w tells the Dial command to wait 0.5 seconds

 

Cyber Security, Reverse Engineering, Tools

Improved proxmark3 scanning of ioProx / Kantech fobs

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I’ve been playing with my new proxmark3. It works great for HID cards, but ioProx code is still in its infancy. I made some improvements to it based on analysis by marshmellow:

  • Better accuracy: You no longer have to worry about centering your fob on the antenna or scan it repeatedly to get a “good” reading. Now you can just hold it in your fingers to scan. Before this update I was averaging 10 – 70% accuracy depending on how I held the fob. This version is pretty much 100% – I haven’t had a bad scan yet.
  • Correct decoding of human readable XSF number: Previous version had a bug that displayed the wrong unique code and the wrong facility IDs.

proxmark3

Download the binary firmware (including source code patch if you want to build it yourself) .

There is still more work to be done. For example, there appears to be CRC or checksum near the end – it’s still a mystery.

Networking, Solved, Tools

Quick and easy iptables based proxy

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Today was a busy day dealing with power outage that affected 2100 businesses in downtown Calgary. Of course, couple of my clients were in the zone that went dark. I offered them to run their key infrastructure from my place for couple of days. Everything went great, except I have only 1 IP address on my connection. That’s not good when both clients want to come in on port 443. What to do?

Call up my ISP and order another IP? Nope: Takes too long, too expensive, I just need this temporarily. Also, ISP might mess it up and take me offline for a while.

Get VM with IPv4 IP and proxy the traffic over? Yes, but why go with something heavy handed like nginx?

I prefer this elegant solution brought to you by iptables:


# echo 1 >| /proc/sys/net/ipv4/ip_forward
# iptables -t nat -A PREROUTING -p tcp -d $IP_OF_VM --dport 443 -j DNAT --to $IP_WHERE_IM_FORWARDING_TO:8443
# iptables -t nat -A POSTROUTING -j MASQUERADE

Cyber Security, Tools

CAPTCHA firewall bypass / port knocking portal

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Couple of my clients’ sites were being probed by botnets.   It was the usual:

  • Common vulnerabilities probes
  • Password guessing attacks

It didn’t warrant putting them behind a firewall, but I also didn’t like the idea of having it open to relentless automated 24×7 scanning. The sites were extranet type of sites, not really public, but not private either.  I scratched my head a bit trying to figure out how I could improve security without inconveniencing users.  What I came up with is this method:

  1. Any access to the website is blocked by a “captive portal” like page
  2. When the user provides the portal what’s being asked for (in this case correct answer to CAPTCHA) the firewall opens an exception to their IP and the user is redirected onward to the site they were looking for.

Is this secure against a determined hacker?  Definitely not.  Solving the CAPTCHA takes only 3 seconds and they’re in through the first layer of defense.   That’s why it’s critical that this is treated as an extra (thin) layer of defense and not as the only layer.

Is this secure against 99% off all attacks out there? (worm / botnet attacks on autopilot): Definitely

How is it implemented?

  • PHP page shows the portal page
  • If CAPTCHA is correct, IP is collected from $_SERVER[“REMOTE_ADDR”], sanitized and saved in a file that keeps track of allowed IPs
  • PHP  page then triggers a shell script that updates iptables with the following entry:
    iptables -t nat -A PREROUTING -p tcp --dport 80 -s $AllowedIP -d $YourIP -j DNAT --to-destination $TargetIP:80

How can this be improved?

Nothing says that access is given with a simple CAPTCHA, there could be full authentication that takes pace before firewall is opened.  Furthermore it could close shortly after access is given disallowing any fresh TCP connections.   Think of it as authenticated port knocking.

security proxy

 

You’ve probably seen a page like this if you’ve stumbled across CloudFlare protected site when using Tor.  I don’t know what internal mechanism they use, but I imagine it’s very similar.

 

Cyber Security, Reverse Engineering, Tools

API Monitors

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When reversing applications it’s useful to see what’s happening under the hood.   Up until now I’ve either had to bring out OllyDbg and dive into assembly or rely on a high level tool like Systernals Process Monitor.   I’m fond of strace on Linux, but when I searched for “strace for Windows” resulted in tools that were not very reliable.   That was couple of years ago.

Today I stumbled on these two API monitors that do exactly what I need on Windows:

 

Cyber Security, Reverse Engineering, Tools

Visualizing Complex Files

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Inspired by a very interesting TED talk by Chris Domas, I decided to make my own tool that did the same thing.

Download the binary (.NET compatible)

Download the source code

As you can tell from the source code,  the mechanism is very easy:

  1. Split file into bytes
  2. Loop through the bytes (currentByte and previousByte)
  3. X axis is 0 – 255 (currentByte)
  4. Y axis is 0 – 255 (previousbyte)
  5. Plot intersections of X and Y

The technical name for this is digraph.  Doing this in 3D or 4D would require a very similar process.

Below are screenshots of some of the files that I visualized.

text

Note how everything is in the upper left corner.  That’s because bulk of plain text is ASCII bytes 32 (space) to 126 (~)

exe

 

Some similarities to a text file in terms of well defined patterns except that binary file won’t be restricted to below byte 127.

jpeg

Notice the shades of gray.

 

random

 

This was about 32 MB file.  If I had a bigger file that was even more random I would expect the entire screen to fill white.   Any pattern visible here is a tale tale to a lack of randomness (or a small sample)

 

 

Networking, Tools

Pingb: Bandwidth Measuring

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Ever needed to get an estimate of a link’s bandwidth and all you have is shell access to one of the end points?

Normally you would need access to both endpoints and run something like iperf across the link.   That’s the proper way, but it takes a lot of time to setup (poke holes through firewalls etc).   If you don’t want to go through that hassle and just need a quick estimate, you can use pingb.

Pingb estimates the bandwidth by measuring the difference between ICMP echo requests of different sizes.

 

Tools

Dance Pad Walking Controller

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After playing Step Mania I realized that my pad might be useful for more than just dancing.  Gaming is such a sedentary activity so why not use the dance pad to actually walk in a game using your own two legs.  My first attempt was adapting the game Exult.  This is how you can make it work:

  • Get your dance pad ready
  • Install AutoHotKey
  • Launch my controller script using AutoHotKey
  • Launch Exult
  • Place the dance pad in a diagonally in front of your computer, Up arrow facing in the NW direction, right arrow facing in the NE direction

  • To walk stand on two arrows at a time and just press one at a time … NW-NE makes avatar walk N. NE-SE walk E … etc. It’s pretty natural after a while. …. basically left-right-left-right just like walking. Of course walking east and west is more of a front-back-front-back kind of an affair, but feels pretty good too.
  • You will soon realize that you don’t have a mouse and keyboard handy. I handled this problem by mapping the start button on the mat to combat toggle and the O button to inventory.
  • For mouse movement I just grabbed a hard writing pad and used it as my mouse pad. It worked pretty well, you can organize your inventory pretty efficiently and if your legs get too tired you can cheat and walk with the mouse.
  • If you have problems it’s probably because of the joystick mapping

Have fun 🙂 … I already finished Trinsic and walked to Britain to pick up my supplies from Lord British. But then I thought I could walk to vesper to pick up the Golden Akhn that Lord British said I could borrow … and the slime got Iolo and then me in the swamp … I should have ran 🙂 … left-right-left-right

Let me know how you like it … it’s definitely a work in progress. One thing that’s especially annoying is controlling walking speed so that in the future the faster you walk the faster your avatar walks.

If you like this, you may like Step Maze