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

[H-1] Anyone can modify first checklist on santasList:checkList, causing incorrect Santa classification

vegazeronos

Root + Impact

Description

  • The checkList function lacks access control, allowing any external account to arbitrarily set the first-check status for any user. This breaks the core trust assumption of the protocol: that only Santa (the privileged authority) can decide whether a user is NICE, EXTRA_NICE, or NAUGHTY. Because the first checklist result is directly consumed by later logic (including eligibility for second checks and present collection), unauthorized mutation of this state enables full privilege escalation.

    An attacker can self-assign EXTRA_NICE status without any interaction from Santa. Since this status is later used as a prerequisite for minting presents or tokens, the attacker bypasses the intended human-in-the-loop validation entirely. This is not a UI or UX issue; it is a fundamental authorization flaw at the smart contract layer. The provided POC demonstrates that a normal user can call checkList directly and permanently alter their own status.

    This vulnerability is especially severe because it undermines all downstream logic. Any protections added later (time checks, second checks, redemption rules) become ineffective if the initial classification is compromised. The contract implicitly assumes that checkList is a trusted write, but this assumption is violated at runtime.

@> function checkList(address person, Status status) external {
// @written onlySanta modifier is not there
// @written there's no check is Santa already checklist or not, to prevent change after the second already submitted
s_theListCheckedOnce[person] = status;
emit CheckedOnce(person, status);
}

Risk

Likelihood:

  • High. The function is publicly callable, requires no special conditions, and is trivial to exploit.

Impact:

  • High. Attackers can illegitimately gain EXTRA_NICE status, leading to unauthorized minting, token inflation, and loss of protocol integrity.

Proof of Concept

Please add this POC on the test file
​
function testAnyoneCanChecklistThemselves() public {
vm.startPrank(user);
santasList.checkList(user, SantasList.Status.EXTRA_NICE);
vm.stopPrank();
​
assertEq(uint256(santasList.getNaughtyOrNiceOnce(user)), uint256(SantasList.Status.EXTRA_NICE));
}
​

Recommended Mitigation

Please add onlySanta modifier on the checkList function

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

Lead Judging Commences

ai-first-flight-judge Lead Judge about 4 hours ago
Submission Judgement Published
Validated
Assigned finding tags:

[H-01] Anyone is able to call `checkList` function in SantasList contract and prevent any address from becoming `NICE` or `EXTRA_NICE` and collect present.

## Description With the current design of the protocol, anyone is able to call `checkList` function in SantasList contract, while documentation says only Santa should be able to call it. This can be considered as an access control vulnerability, because not only santa is allowed to make the first check. ## Vulnerability Details An attacker could simply call the external `checkList` function, passing as parameter the address of someone else and the enum Status `NAUGHTY`(or `NOT_CHECKED_TWICE`, which should actually be `UNKNOWN` given documentation). By doing that, Santa will not be able to execute `checkTwice` function correctly for `NICE` and `EXTRA_NICE` people. Indeed, if Santa first checked a user and assigned the status `NICE` or `EXTRA_NICE`, anyone is able to call `checkList` function again, and by doing so modify the status. This could result in Santa unable to execute the second check. Moreover, any malicious actor could check the mempool and front run Santa just before calling `checkTwice` function to check users. This would result in a major denial of service issue. ## Impact The impact of this vulnerability is HIGH as it results in a broken mechanism of the check list system. Any user could be declared `NAUGHTY` for the first check at any time, preventing present collecting by users although Santa considered the user as `NICE` or `EXTRA_NICE`. Santa could still call `checkList` function again to reassigned the status to `NICE` or `EXTRA_NICE` before calling `checkTwice` function, but any malicious actor could front run the call to `checkTwice` function. In this scenario, it would be impossible for Santa to actually double check a `NICE` or `EXTRA_NICE` user. ## Proof of Concept Just copy paste this test in SantasListTest contract : ``` function testDosAttack() external { vm.startPrank(makeAddr("attacker")); // any user can checList any address and assigned status to naughty // an attacker could front run Santa before the second check santasList.checkList(makeAddr("user"), SantasList.Status.NAUGHTY); vm.stopPrank(); vm.startPrank(santa); vm.expectRevert(); // Santa is unable to check twice the user santasList.checkTwice(makeAddr("user"), SantasList.Status.NICE); vm.stopPrank(); } ``` ## Recommendations I suggest to add the `onlySanta` modifier to `checkList` function. This will ensure the first check can only be done by Santa, and prevent DOS attack on the contract. With this modifier, specification will be respected : "In this contract Only Santa to take the following actions: - checkList: A function that changes an address to a new Status of NICE, EXTRA_NICE, NAUGHTY, or UNKNOWN on the original s_theListCheckedOnce list." The following code will resolve this access control issue, simply by adding `onlySanta` modifier: ``` function checkList(address person, Status status) external onlySanta { s_theListCheckedOnce[person] = status; emit CheckedOnce(person, status); } ``` No malicious actor is now able to front run Santa before `checkTwice` function call. The following tests shows that doing the first check for another user is impossible after adding `onlySanta` modifier: ``` function testDosResolved() external { vm.startPrank(makeAddr("attacker")); // checklist function call will revert if a user tries to execute the first check for another user vm.expectRevert(SantasList.SantasList__NotSanta.selector); santasList.checkList(makeAddr("user"), SantasList.Status.NAUGHTY); vm.stopPrank(); } ```

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