Submitted by zzebra83, also found by MrPotatoMagic, monrel, mojito_auditor, and ladboy233
https://github.com/code-423n4/2024-03-taiko/blob/0d081a40e0b9637eddf8e760fabbecc250f23599/packages/protocol/contracts/L1/hooks/AssignmentHook.sol#L113-L116 
https://github.com/code-423n4/2024-03-taiko/blob/0d081a40e0b9637eddf8e760fabbecc250f23599/packages/protocol/contracts/L1/libs/LibProposing.sol#L85-L87 
https://github.com/code-423n4/2024-03-taiko/blob/0d081a40e0b9637eddf8e760fabbecc250f23599/packages/protocol/contracts/L1/libs/LibProposing.sol#L249-L255
Proposal of new blocks triggers a call to proposeBlock in the libProposing library. In that function, there is this the following block of code:
This sets the params.coinbase variable set by the caller of the function to be the msg.sender if it was empty.
As part of the process of proposal, hooks can be called of type AssignmentHook. An assignment hooks onBlockProposed will be triggered as follows:
Notice how the meta data is passed to this function. Part of the function of the onBlockProposed is to pay the assigned prover their fee and the payee should be the current proposer of the block. this is done as follows:
Notice how if the payment is in ERC20 tokens, the payee will be the variable  _meta.coinbase, and like we showed earlier, this can be set to any arbitrary address by the proposer. This can lead to a scenario as such:
The scenario above describes how someone can be forced maliciously to pay fees for block proposals by other actors.
A simple fix to this to ensure the block proposer will always be the msg.sender, as such:
dantaik (Taiko) confirmed and commented:
