Take a look at https://github.com/code-423n4/2024-03-zksync/blob/4f0ba34f34a864c354c7e8c47643ed8f4a250e13/code/contracts/ethereum/contracts/state-transition/chain-deps/facets/Mailbox.sol#L258-L286
This function eventually gets called when requesting transactions from the L2, note that there is an enforcement that mintVaue is always larger than baseCost + _params.l2Value, note that from here we can see that the msg.value of the L1->L2 transaction must only be part of ETH to be minted inside of transaction processing on the L2, the same thing can be confirmed in the bootloader
Now, the DefaultAccount.sol mistakenly assumes that L1->L2 transactions initiated by external owned accounts (EOAs) provide all necessary functionality, leading to its executeTransactionFromOutside() function being left unimplemented.
This oversight means users cannot access their ETH on L2 if a malicious operator selectively processes only L1->L2 transactions. This scenario not only restricts access to ETH on L2 but also breaches the security principle that guarantees users can initiate transactions from L1 to L2, enabling them to withdraw their assets in anticipation of a potentially harmful upgrade.
Enable the creation of L1->L2 transactions that can draw upon ETH in the L2 balance as part of the transaction value. Alternatively, implement functionality in the DefaultAccount::executeTransactionFromOutside function to ensure it operates as initially intended or this should be clearly documented
