Incident Overview
The attacker:
https://etherscan.io/address/0x13370353…3604af
The transaction behind the attack:
https://etherscan.io/tx/0xa17bbc7c…bf0daa
The attacker:
- flash loaned DAI, USDC, WETH, WBTC on Aave
- invoked the buy() function of Array Finance. The attacker gained 430 ARRAY tokens minted by Array Finance using 45.91 WETH
- invoked the joinPool() function of a closed source contract (Array Collater - 0xa800cda5…5d190d) five times
- deposited 676,410.58 DAI + 679,080.46 USDC + 901.82 WETH + 20 WBTC + 20 renBTC and gained 726.38 aBPT tokens minted by Array Collater
- invoked the sell() function to burn 430 ARRAY tokens and got 77.17 aBPT tokens
- invoked the exitPool() function of the Array Collater
- burned 804.55 aBPT tokens obtained in previous steps and obtained 748,271.55 DAI + 751,225.08 USDC + 997.62 WETH + 22.63 WBTC + 22.74 renBTC
- repaid the flash loan.
The attacker exploited the vulnerability: the price mechanism of the Array Finance depends on the totalSupply of the aBPT token, which is manipulatable.
Incident Report
Protocol Information
Market Context at Time of Hack
What the Attacker Needed to Succeed
Understanding the prerequisites for this type of attack helps auditors identify protocols that are most at risk and helps developers build better defenses.
What Auditors Should Check
If you're auditing a protocol with similar architecture to Array Finance, these are the critical security checks that could have prevented this incident (July 2021).
- Verify all logic paths related to Flash Loan Attack are guarded by proper access controls and input validation - see the Flash Loans Attacks attack class for patterns
- Review privileged functions (owner, admin, governance) for potential abuse vectors - centralization risks should be documented and bounded with timelocks or multi-sigs
Master these auditing techniques with hands-on labs and real exploit scenarios in the Smart Contract Hacking course.
Free TrialRelated Attack Classes
The technique used in this hack maps to these vulnerability classes in our security curriculum:
Sources & References
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01
Source 1 https://array.finance/
- 02
Learn to Prevent the Next Array Finance
The Array Finance hack is one of many attacks that skilled auditors are trained to detect before deployment. Master real exploit patterns and defense techniques with hands-on Web3 security training.