What happened
On August 29, 2021, xToken's Ethereum xSNX product was exploited for an estimated $4.5 million loss to holders. The attacker combined a 25,000-ETH flash loan, SNX borrowing, and trades that sharply depressed the SNX price. They then invoked a rebalance-related xSNXAdmin function that xToken intended to restrict to its dYdX flash-loan integration.
xToken decided to sunset xSNX and said it would calculate investor losses for a compensation program.
How it happened
- The attacker flash-borrowed 25,000 ETH, borrowed approximately 1 million SNX from Aave, and acquired additional SNX on Bancor.
- They sold approximately 1.5 million SNX through Kyber, materially lowering the SNX price, then exchanged the resulting USDC for sUSD.
- The attacker transferred sUSD to xSNXAdmin and called
callFunction, which burned the contract's sUSD debt and exchanged SNX at the artificially depressed price. - They reversed the surrounding trades, repaid the loans, and extracted value through the price distortion and resulting external arbitrage.
Protocol details
Classification
Ecosystem / Token / Oracle Manipulation
Protocol Type
Liquidity manager
Affected asset / contract
XTK
Implementation language
Solidity
Protocol links
Website
@xtokenmarket
Security review history
- ABDK Consulting View report
- CertiK View report
Evidence
- report xSNX Post Mortem medium.com
- report Post-mortem rekt.news
- analysis DeFiLlama defillama.com
Understand the attack patterns
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