Tether's Blacklisted Swap Router Uncovered After Five-Year Silence
Tether's USDT contract has been carrying a built-in blacklist mechanism since its early Ethereum deployment, allowing Tether's contract owner to bar any address from sending USDT out. One such blacklisted address is a contract tagged 'Metamask: Swap Router' on Etherscan, which has been stuck on the blacklist since 2021.
Despite being part of MetaMask Swaps' infrastructure, this contract has gone unnoticed for nearly five years. The discovery came from blockchain security researcher Specter, who cross-referenced contract addresses against blacklist records and noticed the flag.
The 'Metamask: Swap Router' contract is still actively processing swaps on Ethereum, with over 17 million transactions processed to date, while holding a USDT balance of a few thousand dollars. The blacklist prevents it from sending USDT out once received, effectively trapping any stranded USDT mid-route.