SlowMist: UwU Lend Hack Analysis
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SlowMist: UwU Lend Hack Analysis
Attackers exploited a compatibility flaw in the price oracle's direct access to spot market prices and median price calculations to manipulate the price of sUSDE, enabling them to conduct borrowing and liquidations under severely distorted price spreads to obtain unintended profits.
Navigating Web3 tides with focused insightsAuthor: Doris@SlowMist Security Team
Background
On June 10, 2024, according to monitoring by the SlowMist MistEye security system, UwU Lend—an EVM-based digital asset lending platform—was attacked, resulting in losses of approximately $19.3 million. The SlowMist Security Team has analyzed the incident and shares the findings below:
(https://x.com/SlowMist_Team/status/1800181916857155761)
Relevant Information
Attacker address:
0x841ddf093f5188989fa1524e7b893de64b421f47
Vulnerable contract address:
0x9bc6333081266e55d88942e277fc809b485698b9
Attack transactions:
0xca1bbf3b320662c89232006f1ec6624b56242850f07e0f1dadbe4f69ba0d6ac3
0xb3f067618ce54bc26a960b660cfc28f9ea0315e2e9a1a855ede1508eb4017376
0x242a0fb4fde9de0dc2fd42e8db743cbc197ffa2bf6a036ba0bba303df296408b
Core of the Attack
The core of this attack lies in the attacker’s ability to directly manipulate the price oracle for sUSDE tokens through large swaps in CurveFinance pools, thereby influencing the sUSDE token price and exploiting the manipulated price to extract other assets from the lending pool.
Attack Process
1. Flash loan to borrow assets and dump USDE price: The attacker first borrowed a large amount of assets via flash loans, then swapped part of the borrowed USDE tokens into other tokens within a Curve pool that influences the sUSDE price.
2. Open massive borrowing positions: With the sUSDE price now significantly lowered, the attacker deposited other underlying tokens to borrow large amounts of sUSDE tokens.
3. Manipulate the oracle again to inflate sUSDE price: By performing reverse swaps in the same Curve pool, the attacker rapidly increased the sUSDE price.
4. Mass liquidation of debt positions: Due to the sharply inflated sUSDE price, the attacker was able to liquidate previously created debt positions to obtain uWETH.
5. Deposit remaining sUSDE to borrow other underlying tokens: The attacker then deposited the now-high-priced sUSDE to borrow additional underlying tokens for profit.
It is clear that the attacker repeatedly manipulated the sUSDE price—borrowing heavily when prices were low and profiting through liquidations and re-collateralization when prices were high. We traced the sUSDE pricing oracle to the contract sUSDePriceProviderBUniCatch:
The sUSDE price is determined by retrieving 11 different USDE prices from both the CurveFinance USDE pool and the UNI V3 pool, sorting them, and calculating the median value.
Within this logic, 5 of the USDE prices are obtained directly using the get_p function, which fetches the spot price from the Curve pool instantly. This allowed the attacker to directly influence the median price calculation within a single transaction via large-volume swaps.
MistTrack Analysis
According to on-chain tracking tool MistTrack, the attacker address 0x841ddf093f5188989fa1524e7b893de64b421f47 gained approximately $19.3 million from the attack, including ETH, crvUSD, bLUSD, and USDC. Subsequently, all ERC-20 tokens were swapped into ETH.
Tracing gas fee funding sources reveals that the initial capital in the attacker’s address came from a Tornado Cash deposit of 0.98 ETH. The address later received five additional fund transfers from Tornado Cash.
Expanding the transaction graph shows that the attacker transferred 1,292.98 ETH to address 0x48d7c1dd4214b41eda3301bca434348f8d1c5eb6, which currently holds a balance of 1,282.98 ETH. The remaining 4,000 ETH was sent to address 0x050c7e9c62bf991841827f37745ddadb563feb70, which now holds 4,010 ETH.
MistTrack has blacklisted the relevant addresses and will continue monitoring the movement of stolen funds.
Summary
The root cause of this attack was the vulnerability in the price oracle mechanism, which relied on direct spot prices from Curve pools combined with a median-based calculation. This design flaw enabled the attacker to manipulate the sUSDE price and exploit significant price discrepancies to conduct unauthorized borrowing and liquidation for illicit profit. The SlowMist Security Team recommends that projects strengthen the manipulation resistance of their price oracles and implement more secure pricing mechanisms to prevent similar incidents in the future.
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