Saddle Finance Hack

TOTAL LOST $11.0M
High Flash Loan Attacks Ethereum

What happened

On April 30, 2022, a series of Ethereum transactions exploited Saddle Finance's sUSD MetaPool and put roughly $11 million in assets at risk. A whitehat intervention saved part of the affected funds before the malicious transactions drained the remainder. The issue was an incomplete deployment fix: the live sUSD V2 MetaPool was still using an old MetaSwapUtils library with incorrect LP-token price scaling.

Technical Root Cause

The deployed MetaSwapUtils swap calculation did not apply the base pool's virtual price when pricing LP-token inputs and outputs. This made the swap path inconsistent with the intended metapool accounting and created a profitable round-trip trade.

Case & protocol details

Classification Swap Logic / LP Token Pricing
Protocol Type DEX
Affected asset / contract SDL
Smart Contract Language Solidity
Official Website saddle.finance/
Protocol Twitter/X @saddlefinance

Attack Timeline

The attacker used flash liquidity to acquire USDC, moved through sUSD and Saddle LP-token swaps, and repeatedly exploited the pool's distorted accounting. In a correctly implemented metapool, a base-pool LP token is scaled by its virtual price when the swap is priced. Saddle's vulnerable swap path omitted the corresponding scale-up and scale-down operations.

A swap from sUSD to saddleUSD could therefore leave the invariant at an artificially favorable state; swapping back withdrew more sUSD than the attacker supplied. Repeating the cycle compounded the pricing error until the pool's liquidity was drained.

Security review history

Funds Recovery

22.7%

Recovered

$2.5M

Net Loss

$8,503,000

Evidence & learning

Attack pattern

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Flash Loan Attacks

Proof of concept

1 available

Sources and on-chain records

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