Summary

In the documentation its specified that the checkList() is only callable by the Santa.

Vulnerability Details

But here you forget to add the onlySanta modifier in checkList() .

Impact

Any attacker can call the chcekList function and set its initial status either naughty or nice.

POC

Code snippet

       * @notice Do a first pass on someone if they are naughty or nice. 
       * Only callable by santa
       * @param person The person to check
      * @param status The status of the person
        */
function checkList(address person, Status status) external {
    s_theListCheckedOnce[person] = status;
    emit CheckedOnce(person, status);
}

Test Case

   function testCheckList1() public {
    vm.prank(attacker);
    santasList.checkList(user, SantasList.Status.NICE);
    assertEq(uint256(santasList.getNaughtyOrNiceOnce(user)), uint256(SantasList.Status.NICE));
}

Tools Used

Manual Review.

Recommendations

Recommended to add onlySanta modifier in checkList() like this.

    function checkList(address person, Status status) external onlySanta {
    s_theListCheckedOnce[person] = status;
    emit CheckedOnce(person, status);
}