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

[H-3] Anyone can collect a present without being checked by Santa

vegazeronos

Root + Impact

Description

  • The collectPresent function incorrectly allows users who have never been checked by Santa to mint a present. This occurs due to unsafe enum ordering, where the default enum value (0) maps to a valid “nice” state rather than a strictly invalid or uninitialized state. As a result, users who were never processed through checkList or checkTwice are implicitly treated as eligible.


  • In Solidity, uninitialized enums default to the first declared value. Because the enum ordering places a “positive” status before a clearly invalid state, the contract logic mistakenly interprets unchecked users as having passed Santa’s validation. The POC demonstrates that a completely unchecked user can wait until the Christmas timestamp and successfully collect a present.


  • This is a classic uninitialized-state vulnerability that violates the protocol’s intended flow: check → validate → reward. Instead, the flow becomes wait → mint, bypassing all Santa logic.

if (s_theListCheckedOnce[msg.sender] == Status.NICE && s_theListCheckedTwice[msg.sender] == Status.NICE) {

Risk

Likelihood:

  • High. Any user can exploit this by simply waiting until the timestamp.

Impact:

  • High. Unauthorized users can mint NFTs and potentially chain this into further token abuse.

Proof of Concept

Please copy this code to the test file

function testCantCollectPresentBeforeCheckedBySanta() public {
vm.warp(santasList.CHRISTMAS_2023_BLOCK_TIME() + 1);
​
vm.startPrank(user);
santasList.collectPresent();
assertEq(santasList.ownerOf(0), user);
}

Recommended Mitigation

Please change the numeric of the enum, please make NAUGHTY in the first enum, and make NICE the second one

enum Status {
+ NAUGHTY,
NICE,
EXTRA_NICE,
- NAUGHTY,
NOT_CHECKED_TWICE
}
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 4 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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