mitigations.md

Mitigation Strategies Analysis for ethereum/solidity

Mitigation Strategy: Checks-Effects-Interactions Pattern

Description:

1. Checks: Begin each function (especially those interacting with external contracts or handling value) with a series of require statements to validate all preconditions and inputs. Examples:
   • require(balanceOf[msg.sender] >= amount, "Insufficient balance");
   • require(input > 0 && input < maxValue, "Invalid input");
   • require(msg.sender == owner, "Unauthorized");
2. Effects: After all checks, update the contract's state (modify balances, change ownership, etc.). Do this before external calls.
3. Interactions: Finally, interact with other contracts (make external calls).

List of Threats Mitigated:

• Reentrancy (Severity: Critical): Prevents recursive calls before state changes are complete.
• State Inconsistency Issues (Severity: High): Ensures consistent state before external interactions.

Impact:

• Reentrancy: Reduces risk to near zero if implemented correctly.
• State Inconsistency: Significantly reduces likelihood of state-related bugs.

Currently Implemented:

• Example: "Implemented in withdraw() function in Bank.sol, lines 100-115, and in deposit() function, lines 70-80."

Missing Implementation:

• Example: "Missing in processPayment() function in PaymentProcessor.sol, lines 200-220. External call is made before state update."

Mitigation Strategy: Reentrancy Guard (Mutex)

Description:

1. Declare a Lock: bool private _locked;
2. Create a Modifier:

   modifier nonReentrant() {
       require(!_locked, "Reentrancy detected");
       _locked = true;
       _; // Function code executes here
       _locked = false;
   }

3. Apply the Modifier: Add nonReentrant to vulnerable functions.

List of Threats Mitigated:

• Reentrancy (Severity: Critical): Prevents reentrant calls.

Impact:

• Reentrancy: Strong defense, especially in complex scenarios.

Currently Implemented:

• Example: "Implemented as nonReentrant modifier in Utils.sol, line 20. Applied to withdraw() and claimReward() in Staking.sol."

Missing Implementation:

• Example: "Missing in batchTransfer() in Token.sol, lines 150-170."

Mitigation Strategy: SafeMath (Solidity < 0.8.0) / Built-in Overflow Checks (Solidity >= 0.8.0)

Description (Solidity < 0.8.0):

1. Import SafeMath: import "@openzeppelin/contracts/utils/math/SafeMath.sol";
2. Use SafeMath: using SafeMath for uint256;
3. Replace Operators: Use add, sub, mul, div instead of +, -, *, /.

Description (Solidity >= 0.8.0):

1. No Action (Usually): Built-in checks are active.
2. unchecked Blocks (Rare, Use with Caution):

   unchecked {
       // Operations here will NOT revert on overflow/underflow
   }

List of Threats Mitigated:

• Arithmetic Overflow/Underflow (Severity: High): Prevents integer overflows/underflows.

Impact:

• Arithmetic Overflow/Underflow: Eliminates (>= 0.8.0) or significantly reduces (< 0.8.0) the risk.

Currently Implemented:

• Example (>= 0.8.0): "Project uses Solidity 0.8.17; built-in checks are active."

Missing Implementation:

• Example (< 0.8.0): "SafeMath not used in calculateReward() in Rewards.sol, lines 80-90."
• Example (>= 0.8.0): "unchecked block used without justification in MathUtils.sol."

Mitigation Strategy: Avoid Unbounded Loops (Gas Limit Handling)

Description:

1. Identify Loops: Examine all loops, especially those over arrays/mappings.
2. Determine Boundedness: Is the data structure size bounded or unbounded?
3. Implement Limits (for unbounded loops):
   • Fixed-Size Arrays: Use fixed-size arrays if possible.
   • Pagination: Process a limited number of elements per transaction.
   • User-Defined Limits: Allow users to specify a maximum (with a contract-enforced upper bound).
   • Gas Cost Estimation: Estimate gas cost and revert if it exceeds a limit.

List of Threats Mitigated:

• Gas Limit DoS (Severity: High): Prevents running out of gas due to large loops.
• Block Gas Limit DoS (Severity: High): Reduces risk of consuming the entire block gas limit.

Impact:

• Gas Limit DoS / Block Gas Limit DoS: Significantly reduces DoS risk.

Currently Implemented:

• Example: "Pagination implemented in getAllUsers() in UserManager.sol."

Missing Implementation:

• Example: "processRewards() in Rewards.sol iterates over an unbounded array."

Mitigation Strategy: Input Validation (using require)

Description:

1. Identify Inputs: All external function parameters and data from external calls.
2. Define Constraints: Valid range, type, and format for each input.
3. Implement Checks: Use require statements at the start of functions:
   • require(amount > 0, "Amount must be positive");
   • require(userAddress != address(0), "Invalid address");
   • require(data.length <= MAX_DATA_LENGTH, "Data too long");
4. Sanitize Data: If needed (e.g., remove whitespace).

List of Threats Mitigated:

• Various (Severity: Variable): Mitigates many vulnerabilities, including (indirectly) reentrancy, overflow/underflow, DoS, and logic errors.
• Short Address Attack (Severity: High): Validate address length.

Impact:

• Various: Significantly reduces attack surface.

Currently Implemented:

• Example: "Input validation on all function parameters in Token.sol and Exchange.sol."

Missing Implementation:

• Example: "Missing validation for description in createProposal() in DAO.sol."

Mitigation Strategy: Handle External Call Failures (Check Return Values)

Description:

1. Identify Low-Level Calls: Find all call, delegatecall, and send.
2. Check Return Values: Immediately after each call, check the boolean return:

   (bool success, ) = targetAddress.call{value: amount}("");
   require(success, "External call failed");

3. Handle Failure: If success is false, revert, log an event, or try an alternative.
4. Consider try/catch (Solidity >= 0.6.0):

   try IExternalContract(targetAddress).someFunction{value: amount}() {
       // Success
   } catch Error(string memory reason) {
       // Handle revert
   } catch (bytes memory lowLevelData) {
       // Handle low-level data
   }

List of Threats Mitigated:

• Unhandled Exceptions (Severity: High): Prevents inconsistent state after failed calls.
• DoS (Severity: Medium): Prevents exploiting unhandled exceptions.

Impact:

• Unhandled Exceptions / DoS: Significantly reduces risk.

Currently Implemented:

• Example: "All low-level calls in PaymentProcessor.sol have return values checked."

Missing Implementation:

• Example: "sendEther() in Utils.sol doesn't check send() return value."

Mitigation Strategy: Careful use of delegatecall

Description:

1. Understand the Risks: delegatecall executes code in the context of the calling contract's storage. The called contract can overwrite the caller's state.
2. Use with Trusted Contracts Only: Only use delegatecall with contracts you fully trust and control. Never use it with an address provided by a user.
3. Storage Layout Compatibility: If you must use it, ensure storage layouts are compatible to prevent data corruption.
4. Consider Libraries/Proxies: Use established patterns like upgradeable contracts (proxies) that handle delegatecall safely.

List of Threats Mitigated:

• Malicious Code Execution via delegatecall (Severity: Critical): Prevents attackers from hijacking control flow and modifying your contract's state.
• Storage Corruption (Severity: High): Ensures that the called contract doesn't accidentally overwrite important data.

Impact:

• Malicious Code Execution / Storage Corruption: Reduces the risk to near zero if used correctly (i.e., only with trusted contracts).

Currently Implemented:

• Example: "delegatecall is only used within the proxy upgrade pattern, with a trusted implementation contract."
• Example: "No instances of delegatecall are currently used in the project."

Missing Implementation:

• Example: "delegatecall is used in callUntrustedContract() in Vulnerable.sol, taking a user-provided address as input. This is a critical vulnerability."