Sigvex
EVMRemediation2 min read

Missing Events Remediation

How to make critical state changes observable off-chain by emitting events on every privileged mutation.

evmmonitoring

Missing Events Remediation

Overview

Related Detector: Missing Events

Events are how the outside world sees on-chain state change. Ownership transfers, role grants, parameter updates, and pause toggles that mutate state without emitting an event are invisible to explorers, indexers, and monitoring — an incident can unfold with no alert. The remediation is to emit a well-typed event on every privileged mutation.

Before (Vulnerable)

function setFee(uint256 newFee) external onlyOwner {
    fee = newFee;   // silent — no monitor can see the change
}

After (Fixed)

event FeeUpdated(uint256 oldFee, uint256 newFee);

function setFee(uint256 newFee) external onlyOwner {
    emit FeeUpdated(fee, newFee);   // emit before or after; include old and new
    fee = newFee;
}

Index the fields monitors will filter on (addresses, ids) with indexed, and include both the old and new value so a consumer can reconstruct the transition without an archive node.

Common Mistakes

  • Emitting an event for user actions but not for admin actions, which are the ones defenders most need to watch.
  • Logging only the new value, forcing consumers to diff against prior state to know what changed.
  • Marking more than three parameters indexed (the EVM allows at most three topics beyond the signature).

References