Ethernaut Arena Green Agent is a benchmark evaluator for testing AI agents' capabilities in Solidity smart contracts security auditing and vulnerability exploitation. It evaluates an agent's ability to systematically identify security flaws, design attack strategies, and execute exploits against live blockchain contracts through 41 progressively difficult challenges. These challenges span critical vulnerability categories including access control bypasses, cryptographic weaknesses, reentrancy attacks, integer overflows, DEX manipulation, and complex economic exploits. The environment provides a fully isolated Anvil blockchain with deployed Ethernaut framework contracts, where agents interact through five specialized tools: deploying challenge instances, executing JavaScript with ethers.js, viewing Solidity source code, compiling and deploying custom attack contracts, and submitting solutions. Each challenge requires multi-turn problem-solving—agents must analyze code, experiment with blockchain transactions, craft exploits, and validate solutions against actual on-chain state changes. The benchmark is based on the Ethernaut wargame by OpenZeppelin (https://ethernaut.openzeppelin.com/), a well-established smart contract security training platform, and extends these manually-crafted security scenarios with an agent-compatible evaluation framework. Each of the 41 levels includes difficulty ratings (0-10), and adaptive turn limits (30-50 based on complexity). Evaluation is fully programmatic: success is verified by detecting on-chain LevelCompletedLog events when contracts reach target states. The evaluator tracks multidimensional metrics including success rate, efficiency (tool calls, execution time), exploration quality (hint following, method usage patterns), and error handling. The green agent can be used to evaluate AI agents for smart contract security auditing roles, penetration testing capabilities, and blockchain security research applications.