Price per block could increase

[That3Percent]

Here:
https://github.com/edgeandnode/subscription-payments-contract/blob/7b0368e4da25ece37440e0999fbeee652ad8b103/contracts/Subscriptions.sol#L90

there is no "defense" to the consumer for the price per block to increase suddenly. This could be used by a malicious entity to drain funds

[Theodus]

My understanding is that transferFrom requires the sender to first approve the transfer of up to some amount of tokens. The expectation is that the subscriber would only approve the expected amount so an unexpected increase would result in the transaction being reverted.

[That3Percent]

True, but a frequent pattern is to approve an unlimited amount if they expect to repeatedly interact with the contract. Something we should run by experts when the time comes.