Resources

People often ask me "How did you learn how to hack?" The answer: by reading. This page is a collection of the blog posts and other articles that I have accumulated over the years of my journey. Enjoy!

The ERC4337 (Account Abstraction) implementation assumes that UserOperation binds the protocol to run the user's transaction only by the intended user. In particular, being sent directly to the contract on the blockchain from an EOA. In reality, the transaction does NOT have to be run in an isolated context.

Reentrancy guards and flash loans are great examples of this. The state of an executing contract can be modified prior to execution of the UserOperation. In both cases, it would be possible to force the transaction to fail by triggering the reentrancy guard. This would grief users for the gas they spent.

These can be observed by looking at the public transaction mempool or the gossip-offchain ERC4337-specific mempool. Both are valid ways to front-run these calls and are perfectly valid.

Operations like simple transfers on UserOperations are not affected. More complex contracts, such as flash loans and those with reentrancy guards, would have been affected. The discoverers of the vulnerability from TrustSecurity received a $50K bounty. This is at the top of the high category in the program. It was a unique issue identified through a deep understanding of the ERC's context. Good report!