Santa's List
AI First Flight #3
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Submission Details
Severity: high
Valid

Default Enum Values Grant Universal Eligibility, Any Address Can Mint Free NFTs Due to Default NICE Status

firmanregar

Root + Impact

Description

Solidity mappings initialize to zero, and the Status enum defines NICE = 0. This means every address starts with NICE status by default. The collectPresent function checks both mappings for NICE, allowing any address to collect presents without ever being checked by Santa.

The enum ordering in SantasList.sol, combined with the eligibility check in collectPresent. Since both mappings default to 0 (NICE), the condition passes for unchecked addresses.

enum Status {
NICE, // = 0 (default)
EXTRA_NICE, // = 1
NAUGHTY, // = 2
NOT_CHECKED_TWICE // = 3
}
​
if (s_theListCheckedOnce[msg.sender] == Status.NICE &&
s_theListCheckedTwice[msg.sender] == Status.NICE) {
_mintAndIncrement();
return;
}

Risk

Likelihood:

  • High. Deterministic behavior with no setup.

Impact:
Complete bypass of the verification system. Any address can:

  • Mint NFTs without Santa's approval

  • Create unlimited sybil addresses to drain the NFT supply

  • Render the entire checking mechanism meaningless

Proof of Concept

function testUncheckedUserCanCollect() public {
address attacker = makeAddr("attacker");
// Warp past Christmas
vm.warp(santasList.CHRISTMAS_2023_BLOCK_TIME() + 1);
// Attacker was never checked by Santa
assertEq(uint256(santasList.getNaughtyOrNiceOnce(attacker)), 0);
assertEq(uint256(santasList.getNaughtyOrNiceTwice(attacker)), 0);
// But can still collect
vm.prank(attacker);
santasList.collectPresent();
assertEq(santasList.balanceOf(attacker), 1);
}

Recommended Mitigation

Restructure the enum to use a non-eligible default state.
Alternatively, add explicit bool flags to track whether addresses have been checked.

enum Status {
NOT_CHECKED_TWICE, // = 0 (default, ineligible)
NICE, // = 1
EXTRA_NICE, // = 2
NAUGHTY // = 3
}
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 2 hours ago
Submission Judgement Published
Validated
Assigned finding tags:

[H-02] All addresses are considered `NICE` by default and are able to claim a NFT through `collectPresent` function before any Santa check.

## Description `collectPresent` function is supposed to be called by users that are considered `NICE` or `EXTRA_NICE` by Santa. This means Santa is supposed to call `checkList` function to assigned a user to a status, and then call `checkTwice` function to execute a double check of the status. Currently, the enum `Status` assigns its default value (0) to `NICE`. This means that both mappings `s_theListCheckedOnce` and `s_theListCheckedTwice` consider every existent address as `NICE`. In other words, all users are by default double checked as `NICE`, and therefore eligible to call `collectPresent` function. ## Vulnerability Details The vulnerability arises due to the order of elements in the enum. If the first value is `NICE`, this means the enum value for each key in both mappings will be `NICE`, as it corresponds to `0` value. ## Impact The impact of this vulnerability is HIGH as it results in a flawed mechanism of the present distribution. Any unchecked address is currently able to call `collectPresent` function and mint an NFT. This is because this contract considers by default every address with a `NICE` status (or 0 value). ## Proof of Concept The following Foundry test will show that any user is able to call `collectPresent` function after `CHRISTMAS_2023_BLOCK_TIME` : ``` function testCollectPresentIsFlawed() external { // prank an attacker's address vm.startPrank(makeAddr("attacker")); // set block.timestamp to CHRISTMAS_2023_BLOCK_TIME vm.warp(1_703_480_381); // collect present without any check from Santa santasList.collectPresent(); vm.stopPrank(); } ``` ## Recommendations I suggest to modify `Status` enum, and use `UNKNOWN` status as the first one. This way, all users will default to `UNKNOWN` status, preventing the successful call to `collectPresent` before any check form Santa: ``` enum Status { UNKNOWN, NICE, EXTRA_NICE, NAUGHTY } ``` After modifying the enum, you can run the following test and see that `collectPresent` call will revert if Santa didn't check the address and assigned its status to `NICE` or `EXTRA_NICE` : ``` function testCollectPresentIsFlawed() external { // prank an attacker's address vm.startPrank(makeAddr("attacker")); // set block.timestamp to CHRISTMAS_2023_BLOCK_TIME vm.warp(1_703_480_381); // collect present without any check from Santa vm.expectRevert(SantasList.SantasList__NotNice.selector); santasList.collectPresent(); vm.stopPrank(); } ```

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