921 ETH Stuck in zkSync Era: Why the Transfer() Function Fails?

Introduction

Last month, a researcher highlighted on Twitter that Gemholic, a new project on zkSync Era, raised approximately 921 ETH through its token sale. However, these funds became trapped in the smart contract (GemstoneIDO) due to a critical flaw in the transfer() function.

This incident underscores the limitations of Solidity’s transfer() function, which restricts gas usage to 2,300 units. While this suffices for simple transfers, it fails when the recipient’s fallback/receive functions require more gas. Worse, transfer() automatically reverts transactions upon failure, leaving no room for error handling.

The root cause? zkSync Era’s gas dynamics differ from Ethereum’s EVM. Its dynamic gas pricing often exceeds transfer()’s 2,300 gas limit, forcing transactions to revert.

Ether Transfer Methods in Solidity

Here’s a breakdown of Ethereum’s native token transfer methods and their implications:

1. transfer()

• Gas Limit: 2,300 units (fixed).
• Behavior: Reverts entire transaction on failure.
• Use Case: Basic transfers where gas predictability is critical.

payable(_address).transfer(1 ether);  

2. send()

• Gas Limit: 2,300 units (fixed).
• Behavior: Returns bool (does not auto-revert).
• Drawback: Combines gas limits with manual failure checks, reducing usability.

bool success = payable(_address).send(1 ether);  

3. call()

• Gas Limit: Flexible (no hard cap).
• Behavior: Returns (bool, bytes) for granular control.
• Best Practice: Preferred for modern development due to flexibility.

(bool success,) = payable(_address).call{value: 1 ether}("");  

Why call() Dominates:

• Supports complex receive/fallback logic.
• Allows custom failure handling.
• Avoids rigid gas constraints.

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Key Lessons from the zkSync Era Incident

1. Chain-Specific Nuances Matter:

   • EVM-compatible ≠ identical gas behavior.
   • zkSync Era’s dynamic gas model requires adaptive coding.

2. Testing is Non-Negotiable:

   • Testnets simulate real-chain conditions.
   • Audits catch environment-specific risks early.

3. Future-Proof Your Code:

   • Avoid deprecated methods like transfer()/send().
   • Opt for call() unless gas restrictions are intentional.

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FAQs

Q1: Why did the transfer() function fail on zkSync Era?

A: zkSync’s dynamic gas pricing exceeded transfer()’s 2,300 gas limit, causing automatic reverts.

Q2: Is send() safer than transfer()?

A: No—it shares the same gas limits but lacks auto-reversion, increasing failure risks.

Q3: When should I use call()?

A: For most scenarios, especially when recipient contracts have complex logic or gas needs are unpredictable.

Q4: How can I prevent similar issues?

A: Test on target chains pre-launch and undergo third-party audits to identify environment-specific flaws.

Q5: Are smart contracts editable after deployment?

A: No. Immutability makes thorough pre-deployment testing and auditing essential.

Conclusion

The Gemholic incident highlights the pitfalls of assuming cross-chain compatibility. By prioritizing chain-specific testing, adopting flexible methods like call(), and investing in audits, developers can mitigate risks and safeguard user funds.

Key Takeaway: Smart contract security hinges on understanding your deployment environment—never cut corners.

For expert auditing services, consult our technical team.

🌐 AVS Consulting
https://avsconsulting.pro/