$76 000 USD

JULY 2021




"THORChain (RUNE) [is] a decentralized cross-chain transaction protocol." "Creating a secure cross-chain bridge is one of the most important milestones for the industry right now, and the race is on to be the first to provide it." "Founded in 2018, THORChain is a cross-chain exchange that facilitates transactions between the Binance, Ethereum, and Bitcoin blockchains, aiding in a difficult problem of inter-blockchain swaps without being compelled to pay sizable fees each time. This represents a tremendous pain point and the efforts of THORChain have been well-received, pushing up a token from a low of $0.00851264, two years ago, to a high of $20.89 two months ago." "THORChain entered into its guarded “Chaosnet” launch during April, facilitating cross-chain swaps across the Bitcoin, Ethereum, Litecoin, Bitcoin Cash and Binance Chain networks."


"THORChain don't have assets synthetically tied to a price using an oracle, rather arbitrage trading bots and individuals, seeking to squeeze a profit from the price differences of an individual cryptocurrency on different blockchains, keep the liquidity pool's volume high in the midst of regularly large price swings. Passive liquidity providers earn a steady stream of rewards, often representing an APR of 10%+, even after technical considerations like "impermenant loss" that chips away at total return if the tokens, when removed from the liquidity pool, that aren't at 100% at the same radio value as when you first staked them."


"THORChain (RUNE) claims that hackers airdrop UniH tokens to Ethereum addresses as bait to steal RUNE tokens in users' wallets. Hackers have airdropped UniH tokens with malicious contracts to at least 76,000 Ethereum addresses. Once receiving users sell their newly received UniH tokens (or even just approve the sale) on decentralized trading platforms such as Uniswap, the hackers will They can steal any RUNE tokens they have in their wallets. This is because the RUNE token uses a non-standard token contract called "tx.origin". According to Thorchain’s RUNE token contract code “Beware of phishing contracts that may steal tokens by intercepting tx.origin”, it knows that this type of attack may occur."


"Someone is airdropping UniH tokens to ETH ad[d]resses. Just ignore : do not exchange them on UniSwap. If you approve it for swap[p]ing, the contract will drain your wallet."


"Any contract call can drain all your RUNE, no need for approvals or anything. (1) User calls the contract. (2) The contract calls RUNE.transferTo and transfers everything out. That's it, no need for approvals or anything."


"Solidity has a global variable, tx.origin which contains the address of the account that originally sent the call (or transaction). In old days of Solidity, this was used as a way to make sure only a EOA (Externally Owned Account) can make calls to certain functions. So how does it differ from msg.sender? Let's consider following scenario. If account A calls contract B, and B calls contract C, in C msg.sender is contract B and tx.origin is account A." "Contracts that authorize users using the tx.origin variable are typically vulnerable to phishing attacks that can trick users into performing authenticated actions on the vulnerable contract." "That's [a] well known attack vector but sadly $RUNE was still using tx.origin for approve and call method."


"Solution to this would be using ERC20Permit to have approve and transfer done in one call. Check this great article if you want to know more about Permit." "If you think using tx.origin for authentication is a great idea, think twice and read this article again, and again. I don't recommend using tx.origin anywhere in the code and if your current system is using this global variable, please stop everything and refactor your code. You don't want to end up on the news as next protocol which got rekt."


"In just a few hours, hackers have stolen USD 76,000 worth of tokens."

The ThorChain smart contract used tx.origin to validate that a transfer of RUNE tokens originated from the right wallet. However, if the user interacted with another smart contract, which performed the transfer, the tx.origin would originate from them, and the transaction would go through as though they had sent it.


A malicious hacker was airdropping a smart contract token which would initiate a transfer whenever the token was sent or otherwise interacted with, which would drain any RUNE tokens present in that wallet.


As a result, $76k (or more) worth of RUNE was stolen from users. There doesn't appear to have been any way to assist affected users set up.

Sources And Further Reading

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