Ethernaut: Fallout

My take on CTFs

CTFs constitute a crucial part in the process of becoming a successful security researcher as they require from you an eye for details, a good understanding of solidity and great technical skills to perform the attack and capture the flag. The most talented security researchers are great at CTFs, at solving them of course and sometimes at designing them. CTFs will not turn you into a great web3 security researcher over night, but it will surely arm you with good enough technical skills to be able to write decent coded PoCs to have your finding validated and maybe get selected for report.

What is Ethernaut?

Ethernaut is a CTF(Capture The Flag) developed by the openzeppelin team that you most propbably already heard of. If you haven't, consider taking a look at this roadmap https://www.0xjarix.com/if-i-had-to-start-again/
This CTF gathers 31 challenges for the moment, this number keeps increasing so check their website every now and then: https://ethernaut.openzeppelin.com/
Maybe you'll design your challenge one day and send it to the openzeppelin team.

Also why you here?

Of all the kinds of articles I publish, CTF writeups are those I wish you read the least. I am a big advocate of giving everything the time it needs, if you cannot solve a challenge that you know for a contains an intentional bug in such a small codebase, do not expect to do really well in the contests. There are 2 reasons why someone can fail at solving a challenge, and when I say 'fail' I mean giving up and looking at the writeups, knowing damn well these CTFs are not time-bounded. So if you failed you either:

aren't ready for this challenge yet and that is most probably due to the fact that you skipped some steps in the roadmap
are lazy, you read the challenge, read the codebase, maybe not enough times, you had some assumptions maybe, you might have identified some entrypoints or some conditions to bypass or break, but you did not give it enough time, you did not allow yourself to succeed and that's a shame

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StErMi provided us with a github repo to solve ethernaut challenges in foundry, you can fork it, remove his solutions and try solving the challenges just like I'm doing

Fallout

Claim ownership of the contract below to complete this level.

Things that might help

Solidity Remix IDE

Reasoning

Before version V0.4.22, the constructor() keyword did not exist in solidity, the function that would have the name of the contract would be the constructor, what is the main risk when you need to have 2 strings to match in order to achieve something? Right, typos, and that's the issue here: You have a certain Fal1out() function that could have been the constructor as indicated in the comment above, had it been written properly like so: Fallout.
Hence, this function is callable more than once after contract creation, and that's what we are going to do: call it.

💡

Never blindly trust comments in CTF but even more so in audits, they are developers' assumptions of what they're doing.

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Not so fun fact (it's quite saddening to be fair), this is inspired by a real world hack, can you imagine... just because of a typo, that's why the constructor() keyword was introduced. Avoid manual copies as much as you can, prefer using abi.encodeWithSelector over abi.encodeWithSignature for instance.