🛄Claiming on Behalf of Other Users

Airdrops are often used to distribute tokens to a broad set of users, incentivizing early adopters or rewarding loyalty. However, improper implementation of airdrop claim functions can lead to significant vulnerabilities. One such issue arises when airdrop claim functions allow anyone to claim tokens on behalf of other users. While the tokens might be sent to the correct recipient, allowing this behavior can have unintended consequences, especially when smart contracts or externally owned accounts (EOAs) rely on precise control over when and how they claim their tokens.

he Vulnerability: Anyone Can Claim Tokens on Behalf of Others

The vulnerability exists when an airdrop contract’s claim function allows one user to claim tokens on behalf of another, even if the tokens are transferred to the rightful recipient. This can be particularly dangerous in situations where timing is critical, such as in smart contracts that rely on claiming tokens at specific moments or where claiming tokens might result in a taxable event for the user.

What's the issue? Even though the tokens are sent to the correct address (the recipient), allowing anyone to claim them can lead to:

1. Timing Control Issues: The actual token holder loses control over when they claim their tokens. This can be a problem if the recipient wanted to claim tokens at a specific time, such as when gas fees are lower or for tax purposes.

2. Locked Tokens in Smart Contracts: If the recipient is a smart contract that expected to claim tokens using a specific function, but someone else claims on their behalf, the tokens could be locked in the contract indefinitely if there’s no function to transfer them out.

3. Security Risks: Airdrop claim functions might be integrated into other processes, and if someone else can trigger the claim function, it can disrupt expected flows and logic, potentially leading to larger vulnerabilities.

Conclusion

Allowing anyone to claim airdrop tokens on behalf of others might not seem problematic at first, as the tokens are still sent to the correct address. However, the timing of when tokens are claimed is often important for users, particularly for tax reasons or when the recipient is a smart contract with specific token-handling logic. This vulnerability can lead to unintended consequences, such as locked tokens or unwanted taxable events.

By enforcing proper validation checks—such as ensuring the caller is the rightful recipient or introducing a grace period—you can protect your airdrop contracts from abuse. This ensures that users maintain full control over when and how they claim their tokens, improving the security and reliability of the airdrop system.