Q1 The use of pragma in the given contract snippet
pragmasolidity ^0.6.0;contract test {// Assume other required functionality is correctly implemented// Assume this contract can work correctly without modifications across 0.6.x/0.7.x/0.8.x compiler versions}
Q2 The given contract snippet has
pragmasolidity 0.8.4;contract test {// Assume other required functionality is correctly implementedfunctionkill() public {selfdestruct(payable(0x0)); }}
Q3 The given contract snippet has
pragmasolidity 0.8.4;contract test {// Assume other required functionality is correctly implementedmodifieronlyAdmin() {// Assume this is correctly implemented _; }functiontransferFunds(address payable recipient,uint amount) public { recipient.transfer(amount); }}
Q4 In the given contract snippet
pragmasolidity 0.8.4;contract test {// Assume other required functionality is correctly implementedmapping (uint256=>address) addresses;bool check;modifieronlyIf() {if (check) { _; } }functionsetAddress(uint id,address addr) public { addresses[id] = addr; }functiongetAddress(uint id) publiconlyIfreturns (address) {return addresses[id]; }}
Q5 The security concern(s) in the given contract snippet is/are
pragmasolidity 0.8.4;contract test {// Assume other required functionality is correctly implementedmodifieronlyAdmin {// Assume this is correctly implemented _; }functiondelegate (address addr) external { addr.delegatecall(abi.encodeWithSignature("setDelay(uint256)")); }}
Comment:
Controlled delegatecall: delegatecall() or callcode() to an address controlled by the user allows execution of malicious contracts in the context of the caller’s state. Ensure trusted destination addresses for such calls.
Return values of low-level calls: Ensure that return values of low-level calls (call/callcode/delegatecall/send/etc.) are checked to avoid unexpected failures.
Incorrect access control: Contract functions executing critical logic should have appropriate access control enforced via address checks (e.g. owner, controller etc.) typically in modifiers. Missing checks allow attackers to control critical logic.
Account existence check for low-level calls: Low-level calls call/delegatecall/staticcall return true even if the account called is non-existent (per EVM design). Account existence must be checked prior to calling if needed.
Q6 The vulnerability/vulnerabilities present in the given contract snippet is/are
pragmasolidity 0.7.0;import"@openzeppelin/contracts/security/ReentrancyGuard.sol";// which works with 0.7.0contract test {// Assume other required functionality is correctly implemented// For e.g. users have deposited balances in the contract// Assume nonReentrant modifier is always appliedmapping (address=>uint256) balances;functionwithdraw(uint256 amount) externalnonReentrant { msg.sender.call{value: amount}(""); balances[msg.sender] -= amount; }}
Q7 The security concern(s) in the given contract snippet is/are
pragmasolidity 0.8.4;contract test {// Assume other required functionality is correctly implementeduint256privateconstant secret =123;functiondiceRoll() externalviewreturns (uint256) {return (((block.timestamp * secret) % 6) +1); }}
Q8 The security concern(s) in the given contract snippet is/are
pragmasolidity 0.8.4;contract test {// Assume other required functionality is correctly implemented// Contract admin set to deployer in constructor (not shown)address admin;modifieronlyAdmin {require(tx.origin == admin); _; }functionemergencyWithdraw() externalpayableonlyAdmin { msg.sender.transfer(address(this).balance); }}
Q9 The given contract snippet is vulnerable because of
pragmasolidity 0.8.4;contract test {// Assume other required functionality is correctly implementeduint256privateconstant MAX_FUND_RAISE =100ether;mapping (address=>uint256) contributions;functioncontribute() externalpayable {require(address(this).balance != MAX_FUND_RAISE); contributions[msg.sender] += msg.value; }}
Q10 In the given contract snippet, the require check will
pragmasolidity 0.8.4;contract test {// Assume other required functionality is correctly implementedfunctioncallMe (address target) external { (bool success, ) = target.call("");require(success); }}
Q11 The security concern(s) in the given contract snippet is/are
pragmasolidity 0.8.4;contract test {// Assume other required functionality is correctly implemented// Assume admin is set correctly to contract deployer in constructoraddress admin;functionsetAdmin (address_newAdmin) external { admin = _newAdmin; }}
Q12 The security concern(s) in the given contract snippet is/are
pragmasolidity 0.8.4;contract test {// Assume other required functionality is correctly implemented address admin;addresspayable pool;constructor(address_admin) { admin = _admin; } modifieronlyAdmin {require(msg.sender == admin); _; }functionsetPoolAddress(address payable _pool) externalonlyAdmin { pool = _pool; }functionaddLiquidity() payableexternal { pool.transfer(msg.value); }}
Q13 The security concern(s) in the given proxy-based implementation contract snippet is/are
There are no imported contracts that need to be made upgradable (by implementing Initializable).
Import upgradeable contracts in proxy-based upgradeable contracts: Contracts imported from proxy-based upgradeable contracts should also be upgradeable where such contracts have been modified to use initializers instead of constructors.
Unprotected initializers in proxy-based upgradeable contracts: Proxy-based upgradeable contracts need to use public initializer functions instead of constructors that need to be explicitly called only once. Preventing multiple invocations of such initializer functions (e.g. via initializer modifier from OpenZeppelin’s Initializable library) is a must.
Initializing state-variables in proxy-based upgradeable contracts: This should be done in initializer functions and not as part of the state variable declarations in which case they won’t be set.
There's no guarantee that the passed arrays are of same length, so if one would be longer than the other one it can cause an Out Of Bounds error, which is why D is correct.
Calls inside a loop: Calls to external contracts inside a loop are dangerous (especially if the loop index can be user-controlled) because it could lead to DoS if one of the calls reverts or execution runs out of gas. Avoid calls within loops, check that loop index cannot be user-controlled or is bounded.
ERC20 transfer() does not return boolean: Contracts compiled with solc >= 0.4.22 interacting with such functions will revert. Use OpenZeppelin’s SafeERC20 wrappers.
Q15 The vulnerability/vulnerabilities present in the given contract snippet is/are
pragmasolidity 0.8.4;import"https://github.com/OpenZeppelin/openzeppelin-contracts/blob/master/contracts/security/ReentrancyGuard.sol";contract test {// Assume other required functionality is correctly implemented// For e.g. users have deposited balances in the contractmapping (address=>uint256) balances;functionwithdrawBalance() external { msg.sender.call{value: balances[msg.sender]}(""); balances[msg.sender] =0; }}
Q16 The security concern(s) in the given contract snippet is/are
pragmasolidity 0.8.4;contract test {// Assume other required functionality is correctly implemented// Assume that hash is the hash of a message computed elsewhere in contract// Assume that the contract does not make use of chainID or nonces in its logicfunction verify(address signer, bytes32 memory hash, bytes32 sigR, bytes32 sigS, uint8 sigV) internal view returns (bool) {
return signer ==ecrecover(hash, sigV, sigR, sigS);}
Comment:
Signature malleability: The ecrecover function is susceptible to signature malleability which could lead to replay attacks. Consider using OpenZeppelin’s ECDSA library.
Insufficient Signature Information: The vulnerability occurs when a digital signature is valid for multiple transactions, which can happen when one sender (say Alice) sends money to multiple recipients through a proxy contract (instead of initiating multiple transactions). In the proxy contract mechanism, Alice can send a digitally signed message off-chain (e.g., via email) to the recipients, similar to writing personal checks in the real world, to let the recipients withdraw money from the proxy contract via transactions. To assure that Alice does approve a certain payment, the proxy contract verifies the validity of the digital signature in question. However, if the signature does not give the due information (e.g., nonce, proxy contract address), then a malicious recipient can replay the message multiple times to withdraw extra payments. This vulnerability was first exploited in a replay attack against smart contracts [36]. This vulnerability can be prevented by incorporating the due information in each message, such as a nonce value and timestamps
Indistinguishable Chains: This vulnerability was first observed from the cross-chain replay attack when Ethereum was divided into two chains, namely, ETH and ETC [10]. Recall that Ethereum uses ECDSA to sign transactions. Prior to the hard fork for EIP-155 [7], each transaction consisted of six fields (i.e., nonce, recipient, value, input, gasPrice, and gasLimit). However, the digital signatures were not chain-specific, because no chain-specific information was even known back then. As a consequence, a transaction created for one chain can be reused for another chain. This vulnerability has been eliminated by incorporating chainID into the fields.