Thread by @isotile

💾 TECHNICAL THREAD OF NFTs HACK 💾

First of all we need to understand the difference between CALL and DELEGATECALL EVM Opcodes

In a simple way; when you call a contract with delegatecall, it is as if you embed the called function inside the contract itself

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Opensea uses Wyvern Protocol, which is the most optimal fees-wise peer-to-peer exchange protocol

But it has also a disadvantage: when you sign a malicious message, the counter-part can execute that signed message for you

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In order to be able to execute arbitrary code in which two peers agree, the following possibilities must exist within the protocol:

CALL and DELEGATECALL

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⚠️ Hackers only needed ONE signature from you to steal all your approved NFTs

This signature:
#⃣ "My approved Opensea Proxy contract is going to make a DELEGATECALL to the hacker contract function transferNFTs" in unreadable form

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The hackers can execute that transaction whenever they want

And they have generalized the code so that they can calmly choose which NFTs they want to steal from you

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After 28 days of storing signatures, the hackers decided to execute the hack

Their code travels into this diagram till they successfully stole your NFTs

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✅ Proposed solution:
A new signing message standard in which wallets inject the domain at the end of the signature

And older signatures that are not using the new standard appear in red ❌

@MetaMask @myetherwallet @TrustWallet @CoinbaseWallet

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📢 This thread is what we think has happened

Investigation is still ongoing and we should wait to official sources from @opensea

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