Mempool Defenses: The Front-Line
In Web3, the first 12 seconds (one block) are the difference between safety and insolvency.
Mempool Monitoring
A "Sentinel" is a high-speed bot that monitors the public mempool for transactions targeting your sensitive contracts.
Defensive Strategies
- The "Rescue" Front-run: If a malicious transaction is detected, the sentinel broadcasts a "Safety Withdrawal" with a higher gas price (Priority Fee) to move the funds to a secure "Safe Room" before the attacker's transaction can execute.
- Automated Pausing: Many modern protocols include a "Pause" function. A sentinel can automatically call this function if it detects an exploit signature.
Dealing with Private RPCs
Sophisticated attackers use private RPCs (like Flashbots) to bypass the public mempool, making their transactions invisible until they are already included in a block. In this case, defense must move to the Post-Execution phase (blocking further transfers).
🛠 Tactical Activity: Simulated Rescue Mission
Objective: Calculate the window for success.
- Scenario: Attacker broadcasts a 100 ETH drain transaction with a 50 Gwei priority fee.
- Task: If you broadcast a "Pause" transaction with 250 Gwei, what is the probability of winning the block?
- Variable: How does "Flashbots" (private relay) change this calculation for the attacker?