Hardening Agent Wallets: SRA-RiskGate Blocks Malicious ERC-20 Approvals and Injections

The Autonomous Wallet Vulnerability

Under automated agent payment flows (such as the x402 specification), an agent signs typed messages upon receiving a 402 Payment Required header. Because on-chain transactions are irreversible, language models alone should never hold ultimate authorization. Malicious actors leverage prompt injections in memo fields or present unlimited allowance payloads (approve(spender, 2**256 - 1)), which LLMs frequently interpret as routine administrative approvals.

Deterministic Policy Enforcement

The sra-riskgate toolkit enforces deterministic verification before calldata reaches the private key signer:

• Approval Blocking: Only direct transfers are permitted; all approve, permit, and transferFrom calls are placed on permanent hold for manual human review.
• Self-Asserted Claim Rejection: If invoice memos contain self-verifying strings (such as verified offline or risk level: low), the check halts execution. Payers cannot score their own risk.
• EIP-712 Validity Limits: Enforces strict execution time windows (such as a 5-minute x402 validity window) and rejects post-dated or long-duration authorizations.
• Fail-Closed Runtime: Any malformed transaction payload or unexpected network identifier yields a hold decision rather than approve.

Model Context Protocol Integration

Developers using Cursor or Claude Desktop can register the verification gateway as a local Model Context Protocol server without writing custom Python harnesses.