Incident Overview
The attacker's address:
https://etherscan.io/address/0x5676e585…a5f1a3
The transaction behind the exploit:
https://etherscan.io/tx/0xf3158a7e…c50713
NowSwap hack was made possible by an error when updating the smart contract’s code. The original code of the contract contained a value, K, of 1,000 in three different places. The update to the code changed this value in two places but not the third.
This third location was a check of the value of K, but it only checked for a value 1/10 of the actual value. This enabled the attacker to swap 1 wei for 98% of the value stored in the contract.
Stolen funds were deposited into Tornado Cash mixer:
https://bloxy.info/txs/calls_from/0x5676e585…a5f1a3?signature_id=994162&smart_contract_address_bin=0x722122df…5b6967
Incident Report
Protocol Information
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 NowSwap Protocol, these are the critical security checks that could have prevented this incident (September 2021).
- Verify all logic paths related to Other are guarded by proper access controls and input validation
- 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 TrialSecurity Audit History
- Audit Report 1 Report
Sources & References
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