Incident Overview
On October 27, 2025, 402Bridge was exploited for approximately $17,693 USDC after the contract creator's admin private key was compromised. The attacker transferred contract ownership to a malicious address and drained funds from over 200 wallets that had granted token approvals, then bridged the stolen funds through multiple chains to Arbitrum.
The vulnerability stemmed from 402Bridge's operational architecture where admin private keys were stored on an internet-connected backend server to facilitate the x402 mechanism. This mechanism required users to sign transactions via the web interface, which were sent to the backend server to extract funds, perform minting, and return results. During the onboarding process to x402scan.com, storing the admin private key on the server exposed it to potential compromise.
The attacker obtained the admin private key and transferred ownership of the creator contract (0xed1AFc4D…EA9FC5) to a malicious address (0x2b8F9556…6B361F). The new owner then called the transferUserToken function to systematically drain USDC from approximately 200+ wallets that had previously granted unlimited token approvals for minting operations. The exploiter swapped the stolen USDC for ETH and bridged funds multiple times to Arbitrum for laundering.
Creator Contract (Exploited):
Attacker Address (New Owner):
Ownership Transfer Transaction:
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 402bridge, these are the critical security checks that could have prevented this incident (October 2025).
- Verify all logic paths related to Private Key Compromised (Stored Publicly) / 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 402bridge
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