Fractal Protocol exploited via flash loan and reentrancy through Balancer callbacks, extracting $13.7K by manipulating receipt token pricing and vault accounting.
Security & Exploits ·
On May 22, 2026, Fractal Protocol's vault lost approximately $13.7K in a flash loan and reentrancy attack. The protocol's total value locked stood at $97.27K before the exploit. The attacker leveraged an Aave V3 flash loan denominated in USDC.e, chaining calls through Balancer V2 swap callbacks to recursively trigger the vault's deposit and withdrawal functions while manipulating the USDF receipt token's pricing mechanism.
The attack exploited a logic flaw in how Fractal computed token pricing and vault accounting across reentered transactions. The receipt token USDF trades at a fixed daily-accrued price of approximately 1.27 USDC per token, with only a 30-day catch-up window in the price computation function. By looping through Balancer callbacks that minted and burned USDF at the configured rate, the attacker created a mismatch between deposited and withdrawn amounts, extracting value from the vault without triggering protective invariant checks.
The vulnerability stemmed from inadequate safeguards between deposit and withdrawal accounting during recursive swap callbacks. Fractal's implementation did not properly validate the relationship between amounts flowing in and out across reentrant calls, allowing the attacker to drain funds by exploiting the fixed tokenPrice model and rounding behavior in share calculations. No details have emerged regarding recovery efforts or protocol updates.