Bypassing Blockchain Authorization via Unsecured Functions
Note: Since the first part of this series I have also uploaded some further videos on remediation of reentrancy and dealing with compiler versions when working with this hacking blockchain series. Head to the console cowboys YouTube account to check those out. Haha as mentioned before I always forget to post blogs when I get excited making videos and just move on to my next project… So make sure to subscribe to the YouTube if you are waiting for any continuation of a video series.. It may show up there way before here.
Note 2: You WILL run into issues when dealing with Ethereum hacking, and you will have to google them as versions and functionality changes often... Be cognizant of versions used hopefully you will not run into to many hard to fix issues.
In the second part of this lab series we are going to take a look at privacy issues on the blockchain which can result in a vulnerably a traditional system may not face. Since typically blockchain projects are open source and also sometimes viewable within blockchain explorers but traditional application business logic is not usually available to us. With traditional applications we might not find these issues due to lack of knowledge of internal functionality or inability to read private values on a remote server side script. After we review some issues we are going to exploit an authorization issues by writing web3.js code to directly bypass vertical authorization restrictions.
Blockchain projects are usually open source projects which allow you to browse their code and see what's going on under the hood. This is fantastic for a lot of reasons but a developer can run into trouble with this if bad business logic decisions are deployed to the immutable blockchain. In the first part of this series I mentioned that all uploaded code on the blockchain is immutable. Meaning that if you find a vulnerability it cannot be patched. So let's think about things that can go wrong..
A few things that can go wrong:
- Randomization functions that use values we can predict if we know the algorithm
- Hard-coded values such as passwords and private variables you can't change.
- Publicly called functions which offer hidden functionality
- Race conditions based on how requirements are calculated
Since this will be rather technical, require some setup and a lot of moving parts we will follow this blog via the video series below posting videos for relevant sections with a brief description of each. I posted these a little bit ago but have not gotten a chance to post the blog associated with it. Also note this series is turning into a full lab based blockchain exploitation course so keep a lookout for that.
In this first video you will see how data about your project is readily available on the blockchain in multiple formats for example:
- ABI data that allows you to interact with methods.
- Actual application code.
- Byte code and assembly code.
- Contract addresses and other data.
Lab Video Part 1: Blockchain OSINT:
Once you have the data you need to interact with a contract on the blockchain via some OSINT how do you actually interface with it? That’s the question we are going to answer in this second video. We will take the ABI contract array and use it to interact with methods on the blockchain via Web3.js and then show how this correlates to its usage in an HTML file
Lab Video Part 2: Connecting to a Smart Contract:
Time to Exploit an Application:
Exploit lab time, I created an vulnerable application you can use to follow along in the next video. Lab files can be downloaded from the same location as the last blog located below. Grab the AuthorizationLab.zip file:
Lab file downloads:
Ok so you can see what's running on the blockchain, you can connect to it, now what? Now we need to find a vulnerability and show how to exploit it. Since we are talking about privacy in this blog and using it to bypass issues. Lets take a look at a simple authorization bypass we can exploit by viewing an authorization coding error and taking advantage of it to bypass restrictions set in the Smart Contract. You will also learn how to setup a local blockchain for testing purposes and you can download a hackable application to follow along with the exercises in the video..
Lab Video Part 3: Finding and hacking a Smart Contract Authorization Issue:
In this part of the series you learned a lot, you learned how to transfer your OSINT skills to the blockchain. Leverage the information found to connect to that Smart Contract. You also learned how to interact with methods and search for issues that you can exploit. Finally you used your browsers developer console as a means to attack the blockchain application for privilege escalation.