Global Shared s_earnTimer State Mutated Across All Users and by buySnow, Causing Protocol-Wide Denial of Service
Description
In Snow.sol:29-38, s_earnTimer is stored as a single global uint256 state variable rather
than a per-user mapping:
// src/Snow.sol
@> uint256 private s_earnTimer;
function buySnow(uint256 amount) external payable canFarmSnow {
...
@> s_earnTimer = block.timestamp;
emit SnowBought(msg.sender, amount);
}
function earnSnow() external canFarmSnow {
@> if (s_earnTimer != 0 && block.timestamp < (s_earnTimer + 1 weeks)) {
revert S__Timer();
}
_mint(msg.sender, 1);
@> s_earnTimer = block.timestamp;
}
Global Lockout: When User A calls earnSnow(), s_earnTimer is updated globally. All
other users in the world are locked out from calling earnSnow() for 7 days. Only 1 user
globally can earn Snow per week.Permanent DoS via buySnow: Every call to buySnow resets s_earnTimer = block.timestamp.
If anyone buys Snow at least once a week (or an attacker periodically calls buySnow(1) for
negligible fee), block.timestamp >> VARIABLES
address private s_collector;
- uint256 private s_earnTimer;
+ mapping(address => uint256) private s_lastEarned;
uint256 public s_buyFee;
uint256 private immutable i_farmingOver;
@@ -84,15 +84,13 @@ contract Snow is ERC20, Ownable {
_mint(msg.sender, amount);
}
- s_earnTimer = block.timestamp;
-
emit SnowBought(msg.sender, amount);
}
function earnSnow() external canFarmSnow {
- if (s_earnTimer != 0 && block.timestamp < (s_earnTimer + 1 weeks)) {
+ if (s_lastEarned[msg.sender] != 0 && block.timestamp < (s_lastEarned[msg.
sender] + 1 weeks)) {
revert S__Timer();
}
_mint(msg.sender, 1);
- s_earnTimer = block.timestamp;
+ s_lastEarned[msg.sender] = block.timestamp;
}
Lead Judging Commences
[L-02] Global Timer Reset in Snow::buySnow Denies Free Claims for All Users
## Description: The `Snow::buySnow` function contains a critical flaw where it resets a global timer `(s_earnTimer)` to the current block timestamp on every invocation. This timer controls eligibility for free token claims via `Snow::earnSnow()`, which requires 1 week to pass since the last timer reset. As a result: Any token purchase `(via buySnow)` blocks all free claims for all users for 7 days Malicious actors can permanently suppress free claims with micro-transactions Contradicts protocol documentation promising **"free weekly claims per user"** ## Impact: * **Complete Denial-of-Service:** Free claim mechanism becomes unusable * **Broken Protocol Incentives:** Undermines core user acquisition strategy * **Economic Damage:** Eliminates promised free distribution channel * **Reputation Harm:** Users perceive protocol as dishonest ```solidity function buySnow(uint256 amount) external payable canFarmSnow { if (msg.value == (s_buyFee * amount)) { _mint(msg.sender, amount); } else { i_weth.safeTransferFrom(msg.sender, address(this), (s_buyFee * amount)); _mint(msg.sender, amount); } @> s_earnTimer = block.timestamp; emit SnowBought(msg.sender, amount); } ``` ## Risk **Likelihood**: • Triggered by normal protocol usage (any purchase) • Requires only one transaction every 7 days to maintain blockage • Incentivized attack (low-cost disruption) **Impact**: • Permanent suppression of core protocol feature • Loss of user trust and adoption • Violates documented tokenomics ## Proof of Concept **Attack Scenario:** Permanent Free Claim Suppression * Attacker calls **buySnow(1)** with minimum payment * **s\_earnTimer** sets to current timestamp (T0) * All **earnSnow()** calls revert for **next 7 days** * On day 6, attacker repeats **buySnow(1)** * New timer reset (T1 = T0+6 days) * Free claims blocked until **T1+7 days (total 13 days)** * Repeat step **4 every 6 days → permanent blockage** **Test Case:** ```solidity // Day 0: Deploy contract snow = new Snow(...); // s_earnTimer = 0 // UserA claims successfully snow.earnSnow(); // Success (first claim always allowed) // Day 1: UserB buys 1 token snow.buySnow(1); // Resets global timer to day 1 // Day 2: UserA attempts claim snow.earnSnow(); // Reverts! Requires day 1+7 = day 8 // Day 7: UserC buys 1 token (day 7 < day 1+7) snow.buySnow(1); // Resets timer to day 7 // Day 8: UserA retries snow.earnSnow(); // Still reverts! Now requires day 7+7 = day 14 ``` ## Recommended Mitigation **Step 1:** Remove Global Timer Reset from `buySnow` ```diff function buySnow(uint256 amount) external payable canFarmSnow { // ... existing payment logic ... - s_earnTimer = block.timestamp; emit SnowBought(msg.sender, amount); } ``` **Step 2:** Implement Per-User Timer in `earnSnow` ```solidity // Add new state variable mapping(address => uint256) private s_lastClaimTime; function earnSnow() external canFarmSnow { // Check per-user timer instead of global if (s_lastClaimTime[msg.sender] != 0 && block.timestamp < s_lastClaimTime[msg.sender] + 1 weeks ) { revert S__Timer(); } _mint(msg.sender, 1); s_lastClaimTime[msg.sender] = block.timestamp; // Update user-specific timer emit SnowEarned(msg.sender, 1); // Add missing event } ``` **Step 3:** Initialize First Claim (Constructor) ```solidity constructor(...) { // Initialize with current timestamp to prevent immediate claims s_lastClaimTime[address(0)] = block.timestamp; } ```
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