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

The bug allowed the hacker to borrow $1.6 million despite depositing just one GMX token worth $70.

AccessTimeIconMar 10, 2023 at 11:15 a.m. UTC
Updated May 9, 2023 at 4:10 a.m. UTC
10 Years of Decentralizing the Future
May 29-31, 2024 - Austin, TexasThe biggest and most established global hub for everything crypto, blockchain and Web3.Register Now

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.

Disclosure

Please note that our privacy policy, terms of use, cookies, and do not sell my personal information has been updated.

CoinDesk is an award-winning media outlet that covers the cryptocurrency industry. Its journalists abide by a strict set of editorial policies. In November 2023, CoinDesk was acquired by the Bullish group, owner of Bullish, a regulated, digital assets exchange. The Bullish group is majority-owned by Block.one; both companies have interests in a variety of blockchain and digital asset businesses and significant holdings of digital assets, including bitcoin. CoinDesk operates as an independent subsidiary with an editorial committee to protect journalistic independence. CoinDesk offers all employees above a certain salary threshold, including journalists, stock options in the Bullish group as part of their compensation.

Oliver Knight

Oliver Knight is a CoinDesk reporter based between London and Lisbon. He does not own any crypto.


Learn more about Consensus 2024, CoinDesk's longest-running and most influential event that brings together all sides of crypto, blockchain and Web3. Head to consensus.coindesk.com to register and buy your pass now.