Resupply Exploit Post-Mortem: How Olympix Could Have Prevented the $9.56M Loss
On June 26, 2025, Resupply, a decentralized lending protocol operating as a sub-DAO of Convex and Yearn Finance, lost $9.56 million in a devastating attack that unfolded in just 90 minutes. The exploit targeted a newly deployed cvcrvUSD vault, leveraging a classic donation attack to manipulate exchange rates and drain the protocol's entire treasury.
Timeline of the Attack
12:18 AM - New crcrvUSD vault deployed with ERC-4626 vault contracts 1:53 AM - Attacker executes exploit, stealing $9.56 million 2:53 AM - Protocol initiates emergency response, setting borrow limits to zero
How the Attack Unfolded
Step 1: Flash Loan Setup
The attacker began by borrowing $4,000 USDC from Morpho through a flash loan, converting it to 4,000 crvUSD to fund the manipulation.
Step 2: The Donation Manipulation
With the flash loan in hand, the attacker executed a classic ERC-4626 donation attack:
Donated 2,000 crvUSD directly to the newly deployed, empty vault contract
Deposited 2 crvUSD to mint just 1 wei of cvcrvUSD shares
This single wei now represented the entire donated amount in the vault's accounting system, creating a massively inflated share price of 2,000,000,000,000,000,001,998,001,998,001,998.
Step 3: Exchange Rate Manipulation
When the ResupplyPair contract's _updateExchangeRate() function calculated the exchange rate, it used the following formula:
Vulnerability Details: The contract calculates the collateral exchange rate using 1e36 / IOracle(...).getPrices(...). This calculation uses integer division and lacks protection against price manipulation. An attacker can exploit a low-liquidity ERC4626 collateral vault via a donation attack to inflate the price reported by the oracle. If the reported price exceeds 1e36, the calculated _exchangeRate rounds down to zero.
Critical Impact: A zero exchange rate causes _isSolvent() to always return true, effectively disabling all LTV checks and allowing an attacker to borrow unlimited funds against negligible collateral, draining the pair contract.
Recommended Mitigation: Add a zero-check on the calculated exchange rate and ensure newly created markets are properly initialized to prevent price manipulation.
How Olympix Could Have Prevented This Exploit
1. Audit Agent Detection
Olympix's internal audit agent autonomously analyzes smart contracts to identify complex logic errors and economic attack vectors. Our audit agent identified the exact vulnerability that led to the $9.56 million loss:
Missing validation checks on the exchange rate calculation
Integer division vulnerability that could result in zero values
Solvency bypass risk through LTV calculation manipulation
By running Olympix's audit agent during the development or pre-deployment phase, the Resupply team would have been alerted to this critical flaw before deploying the vault to mainnet.
2. Automated Unit Testing
Olympix generates comprehensive unit tests that cover edge cases and attack scenarios. For this vulnerability, our automated testing would have created test cases including:
Exchange rate calculations with inflated oracle prices
Donation attacks on empty or low-liquidity vaults
Solvency checks with zero or near-zero exchange rates
Borrowing attempts with negligible collateral
These tests would have immediately exposed the flawed logic in the _updateExchangeRate() and _isSolvent() functions.
3. Mutation Testing for Logic Validation
Olympix's mutation testing systematically modifies code to ensure test suites catch real bugs. For the Resupply vulnerability, mutation testing would have:
Removed or modified the exchange rate calculation to verify proper validation
Tested boundary conditions where division results in zero
Validated that the test suite catches missing sanity checks
This would have revealed that existing tests failed to catch the integer division edge case.
4. Continuous Security Integration
Unlike traditional audits that provide a one-time snapshot, Olympix integrates directly into the development workflow:
Real-time feedback as developers write code
Automated security checks on every commit
Pre-deployment verification before mainnet launch
This shift-left security approach means vulnerabilities are caught and fixed during development, not discovered in production by attackers.
The Core Problem: Empty Vault Deployment
ERC-4626 vaults calculate share prices based on the ratio of assets to shares. In empty or near-empty vaults, this creates a dangerous scenario:
Normal vault: 1,000 shares represent 1,000 tokens = 1:1 ratio Empty vault after donation: 1 share represents 2,000 tokens = 1:2,000 ratio
This inflated ratio breaks price calculations, enabling the exploit. The vulnerability was entirely preventable through proper initialization practices.
Key Takeaways
This exploit demonstrates a fundamental truth about DeFi security: 90% of exploited smart contracts were previously audited. Traditional point-in-time audits are insufficient to protect against well-known attack patterns like donation attacks.
The Resupply hack was entirely preventable through:
Proper vault initialization - Seeding new vaults with initial liquidity makes donation attacks economically unfeasible
Exchange rate validation - Adding simple sanity checks like require(_exchangeRate > 0) would have blocked the exploit
Virtual shares implementation - Using virtual shares prevents empty vault manipulation from deployment
Continuous security monitoring - Automated tools that catch vulnerabilities before deployment, not after exploitation
How to Protect Your Protocol
The difference between a $9.56 million loss and a secure deployment comes down to integrating security throughout the development lifecycle:
Automated audit agents to identify logic errors and economic vulnerabilities
Automated unit testing to validate edge cases and attack scenarios
Mutation testing to ensure test suites actually catch bugs
Pre-deployment validation to verify security before mainnet launch
A $4,000 flash loan became a $9.56 million theft because of missing validation checks and improper vault initialization. With Olympix's proactive security tools integrated into the development process, this vulnerability would have been identified and fixed before the vault ever went live, saving Resupply and its users from a devastating loss.
In DeFi, security isn't just about reviewing code after it's written. It's about building security into every step of the development process, catching vulnerabilities before attackers do.
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Follow-up: Conduct a follow-up review to ensure that the remediation steps were effective and that the smart contract is now secure.
Follow-up: Conduct a follow-up review to ensure that the remediation steps were effective and that the smart contract is now secure.
In Brief
Remitano suffered a $2.7M loss due to a private key compromise.
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Rocketswap’s private keys were inadvertently deployed on the server.
Hacks
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Huobi | Amount Lost: $8M
On September 24th, the Huobi Global exploit on the Ethereum Mainnet resulted in a $8 million loss due to the compromise of private keys. The attacker executed the attack in a single transaction by sending 4,999 ETH to a malicious contract. The attacker then created a second malicious contract and transferred 1,001 ETH to this new contract. Huobi has since confirmed that they have identified the attacker and has extended an offer of a 5% white hat bounty reward if the funds are returned to the exchange.
