This same vulnerability was identified by Trail of Bits in their audit of the project 'Meson Fi'. Severity = high (for obvious reasons) and this vulnerability was a lot more succinct than the one that's in the Gnosis Safe contracts.

1. They identify two functions in the code. One verifies a signature for a "request", the other verifies a signature for a "release message".

2. The request has only the encoded swap, the release has the hash of an encoded swap + recipient's address.

3. First function looks for keccak256(abi.encodePacked(bytes28(0x1945...), encodedSwap)); and second function looks for keccak256(abi.encodePacked(bytes28(0x1945...), keccak256(abi.encodePacked(encodedSwap, recipient)). Difference is in what gets concatenated with the 0x1945 (EIP-191 signature standard) prefix.

Here, the analogy is that within Safe contracts, a product (`return` statement) of the encodeTransactionData function is analogous with encodedSwap.