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

Default enum value `NICE = 0` → all uninitialized addresses are treated as NICE and can collect presents without Santa's check

aiada

Description

  • Normal: Only children who have been checked by Santa (twice, with matching status) should be able to collect presents.

  • Bug: The Status enum has NICE as its first value (0). In Solidity, all uninitialized mapping values default to 0. This means s_theListCheckedOnce[anyAddr] and s_theListCheckedTwice[anyAddr] both return Status.NICE for any address that Santa has NEVER checked.

// src/SantasList.sol:69-74
enum Status {
NICE, // = 0 ← Solidity default — every address starts as NICE!
EXTRA_NICE, // = 1
NAUGHTY, // = 2
NOT_CHECKED_TWICE // = 3
}
// src/SantasList.sol:153-156 — This check passes for ANY uninitialized address!
if (s_theListCheckedOnce[msg.sender] == Status.NICE
&& s_theListCheckedTwice[msg.sender] == Status.NICE) {
_mintAndIncrement(); // Free NFT for anyone!
return;
}

Risk

Likelihood: Every Ethereum address automatically qualifies as NICE without any action from Santa. No preconditions needed.

Impact: Any address can call collectPresent() after Christmas and receive a free NFT, completely bypassing the entire Santa checking mechanism. The gift distribution system is fundamentally broken.

Proof of Concept

function test_AnyoneIsNiceByDefault() public {
// attacker has NEVER been checked by Santa — no checkList, no checkTwice
address attacker = makeAddr("attacker");
​
vm.warp(1_703_480_382); // Christmas 2023
​
vm.prank(attacker);
santasList.collectPresent(); // ✅ SUCCEEDS — attacker gets free NFT!
​
assertEq(santasList.balanceOf(attacker), 1);
}

Run with:

forge test --match-test test_AnyoneIsNiceByDefault -vvv

Result: [PASS] test_AnyoneIsNiceByDefault() — vulnerability confirmed.

Recommended Mitigation

Add an UNKNOWN status as the first enum value (default 0):

enum Status {
+ UNKNOWN, // = 0 — safe default
NICE, // = 1
EXTRA_NICE, // = 2
NAUGHTY, // = 3
NOT_CHECKED_TWICE // = 4
}
Updates

Lead Judging Commences

ai-first-flight-judge Lead Judge 3 days 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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