Description

The approve() function can be vulnerable to a specific attack, where a malicious actor can double spend tokens. This scenario occurs when the owner changes the approved allowance from N to M (N>0, M>0). The malicious spender can observe this change and quickly transfer the original N tokens before the change is mined, and then spend the additional M tokens afterwards. This could result in a total transfer of N+M tokens, which is not what the owner intended. More info you can see in this link.

For this reason, it's recommended to use safeIncreaseAllowance() or safeDecreaseAllowance() for better control. If these methods are not available, using safeApprove() is also an option as it reverts if the current approval is not zero, providing an additional layer of security.