What happened
On April 11, 2023, Paribus was exploited on Arbitrum through cross-market reentrancy in its Compound-style lending implementation. The attacker used a flash loan to establish collateral, triggered a pETH redemption whose ETH transfer occurred before the collateral balance update, and borrowed from the pUSDT and pWBTC markets while that collateral still appeared available. Paribus paused the platform after notification of the exploit.
How it happened
- The attacker took a flash loan of 200 ETH and 30,000 USDT, then deposited those assets as collateral in Paribus markets.
- The attacker borrowed ETH and called the pETH redeem path.
- The pETH redemption sent ETH before updating the redeemer's stored collateral balance, so the attacker's fallback was invoked while the pETH position still appeared collateralized.
- During that callback, the attacker borrowed from the separate pUSDT and pWBTC markets using the stale pETH collateral state, then completed the transaction and repaid the flash loan.
Protocol details
Classification
Borrowing and Lending / Reentrancy
Protocol Type
Lending
Affected asset / contract
pUSDT
Implementation language
Solidity
Protocol links
Website
@paribus_io
Understand the attack patterns
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