Incident Overview
The private key controlling BSC and Polygon deployments was compromised, allowing attackers to transfer ownership of the core bZx contracts and withdraw users' deposited collateral.
The attackers initiated the exploit by transferring ownership of the core bZx contracts. This was done by invoking the target contract with a method through a fallback function with delegatecall. This allowed the attackers to withdraw users' deposited collateral from interest iTokens into another address. The same method was used on the Polygon chain.
Involved addresses:
- Exploiter 1: 0x74487eed…5254d4
- Exploiter 2: 0x0acc0e5f…f35fa5
- Exploiter 3: 0x967bb571…737e31
- Exploiter 4: 0x6551fb9b…e8dd0e
The transaction behind the attack:
- setTerget(): https://bscscan.com/tx/0x57e4aa5f…d52199
- transferOwnership(): https://bscscan.com/tx/0x9b16f5e8…bf01b9
- iDOGE => DOGE: https://bscscan.com/tx/0xd1cff35d…1ec18d
- iETH => ETH: https://bscscan.com/tx/0xa288f212…50ca88
- iBNB => BNB: https://bscscan.com/tx/0x2dbb3df6…597b6a
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 bZx, these are the critical security checks that could have prevented this incident (November 2021).
- Verify all logic paths related to Access Control are guarded by proper access controls and input validation - see the Access Control 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
Learn to Prevent the Next bZx
The bZx 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.