Skip to main content

Incorrect Nonce Update (Signature Replay Attack)

What it detects​

This detector searches for signature verification logic that fails to increment or store the used nonce. Attackers can replay old signatures to repeat privileged actions.

Typical symptoms​

  • Nonce value read but never updated
  • Multiple transactions succeed with the same signature

Solidity snippet (v0.8.25)​

pragma solidity ^0.8.25;

contract Signing {
    mapping(address => uint256) public nonces;
    
    function exec(address user, uint8 v, bytes32 r, bytes32 s) external {
        // nonce not incremented after use
        bytes32 hash = keccak256(abi.encode(user, nonces[user]));
        address signer = ecrecover(hash, v, r, s);
        require(signer == user, "bad sig");
    }
}

Why it matters on EVM​

Without proper nonce updates, attackers can replicate actions and drain funds or change state repeatedly with the same signed message.