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

never-checked addresses pass the NICE gate (broken 'checked twice' invariant)

hatchworker

Root + Impact

Description

  • Normal behavior: only addresses that Santa personally checked twice as NICE should be able to call collectPresent and receive an NFT. The "checked twice" workflow is the protocol's core eligibility invariant.

  • The issue: the enum definition makes NICE (value 0) identical to the default mapping value, so any address Santa never touched reads as NICE on both lists:

    @> enum Status { NICE, EXTRA_NICE, NAUGHTY, NOT_CHECKED_TWICE }
    ​
    if (s_theListCheckedOnce[msg.sender] == Status.NICE && s_theListCheckedTwice[msg.sender] == Status.NICE) {
    _mintAndIncrement();
    return;
    }

    NOT_CHECKED_TWICE = 3 is never used as a default — both status mappings return 0 (NICE) for never-checked addresses. Any address, with zero interaction from Santa, passes the NICE gate after Christmas and mints an NFT. The entire naughty/nice gating is bypassed.

Risk

  • Reason 1 // Solidity mappings default every key to value 0, and Status.NICE is enum value 0.

  • Reason 2 // The gate in collectPresent compares both mappings against Status.NICE with no "has been checked" flag.

  • Impact 1 // Anyone can call collectPresent() after Christmas and mint an NFT without ever appearing on Santa's list.

  • Impact 2 // The protocol's core eligibility mechanism is fully bypassed; attacker needs no privileges.

Proof of Concept

PoC verified by a passing Foundry test (test_PoC_H2_NeverCheckedAddressCanCollectPresent): a fresh address with no list entries calls collectPresent and succeeds; balanceOf == 1.

Recommended Mitigation

Reorder the enum so 0 is an explicit "unchecked" state, e.g.:

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

Or require a separate hasBeenChecked flag before comparing against Status.NICE.

Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge about 1 hour 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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