DeFi Protocol Tender.fi Hacker Returns $1.6M Following Pricing Oracle Glitch

A white hat hacker who targeted decentralized-finance (DeFi) platform Tender.fi has returned $1.6 million that was stolen on Tuesday, receiving a 62.15 ether (ETH) bug bounty worth $850,000 instead.

The attack occurred after Tender.fi upgraded its price feed to relay data from a Chainlink pricing oracle as opposed to a time-weighted average price (TWAP). Tender.fi's code, which was audited by PeckShield, contained an error and returned a number with too many zeros behind it. That meant the attacker was able to deposit one GMX token, worth around $70, effectively tricking the system into allowing infinite borrows, according to a postmortem published on Tender.fi's Medium page. There was no issue with the Chainlink oracle itself.

After extracting $1.6 million from the protocol, the hacker left an on-chain message: "It looks like your oracle was misconfigured. Contact me to sort this out."

Tender.fi reached out and agreed to pay the white hat hacker the bug bounty.

The protocol plans to deploy a new rewritten oracle contract before unpausing borrowing. It has also vowed to repay any unpaid debt left behind by the hacker.

The TND token, which plunged by 34% on Tuesday, was recently trading at $1.87. It has increased by 2.4% in the past 24-hours against its ethereum pair but remains down by 7.6% against its U.S. dollar pair following a crypto market rout.

UPDATE (March 10, 2023, 14:08 UTC): Updates headline and clarifies in second paragraph that the bug was related to Tender.fi's code and not the Chainlink oracle.