Incident Overview
On March 3, 2026, the V4 Swap Router by z0r0z on Ethereum suffered a $42,606 exploit when an attacker bypassed authorization checks in the swap() function by crafting non-standard ABI-encoded calldata that exploited hardcoded calldata offsets in an assembly block, draining USDC from wallets that had approved the router.
The V4 Swap Router contained a critical vulnerability in its swap() function's assembly block, which used hardcoded calldata offsets assuming standard ABI encoding. The attacker crafted non-standard ABI-encoded calldata that deviated from the expected encoding format, allowing them to bypass the router's authorization checks. By manipulating the calldata structure, the attacker exploited the hardcoded offset assumption in the assembly code to pass validation without proper authorization. This enabled draining 42,606.96 USDC from user wallets that had previously approved the router contract.
Blockchain Data Reference
Exploit tx:
https://etherscan.io/tx/0xfe34c4be…ab466a
Exploiter:
https://etherscan.io/address/0xd6b7e831…fa9916
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 V4 Swap Router by z0r0z, these are the critical security checks that could have prevented this incident (March 2026).
- 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
- 01
- 02
Learn to Prevent the Next V4 Swap Router by z0r0z
The V4 Swap Router by z0r0z 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.