🚔Vulnerability of Allowing Unauthorized Withdrawals in Vesting Contracts

Vesting contracts play a crucial role in distributing tokens over time, ensuring that recipients only receive their allocated tokens after meeting certain conditions, such as time-based unlocks. However, improper implementation of the withdrawal logic in these contracts can introduce a serious vulnerability: allowing anyone to withdraw the vested amount on behalf of someone else. This can result in unwanted behavior, especially when tokens are locked in smart contracts that expect to claim their own vested tokens.

In this tutorial, we will explore how this vulnerability occurs, why it can be problematic, and how to implement a proper fix to prevent unauthorized withdrawals in vesting contracts.

Unauthorized Withdrawals on Behalf of Others

A common vulnerability in vesting contracts arises when the withdrawal function allows anyone to trigger the release of vested tokens on behalf of another user or contract. While the tokens are usually sent to the correct recipient, allowing external parties to trigger these withdrawals can cause issues, particularly for smart contracts that rely on claiming their own tokens.

Mitigating the Vulnerability: Restricting Withdrawals

To prevent this vulnerability, you should ensure that only the rightful beneficiary (or a designated actor) can withdraw the vested tokens. This can be achieved by restricting the withdrawVested function so that only the owner of the vested tokens (or an approved entity) can trigger the withdrawal.

Conclusion

Allowing anyone to withdraw vested tokens on behalf of others can lead to significant issues, especially when interacting with smart contracts. Tokens may become locked or lost if the smart contract expects to claim its tokens in a specific way, but another party triggers the withdrawal prematurely.

To mitigate this vulnerability:

• Restrict withdrawal functions so that only the rightful token owner can trigger them.

• Implement an optional approval system for delegated withdrawals if needed.

• Ensure smart contracts can safely claim their tokens without interference