Introducing Ayeixa MCP Guardian: Capability Fencing & Parameter Sanitization for MCP

Introducing Ayeixa MCP Guardian: Capability Fencing & Parameter Sanitization for MCP Model Context Protocol (MCP) empowers language models to interact directly with databases, filesystems, and CLI utilities. However, exposing tool APIs creates security vulnerabilities: unauthorized directory traversal (../../etc/passwd), destructive shell commands (rm -rf), and untracked actions. Ayeixa MCP Guardian (@ayeixa/mcp-guardian) is a runtime capability fence and parameter sanitization middleware for Model Context Protocol servers and client tool invocations. GitHub Repository: https://github.com/alpallovy/ayeixa-mcp-guardian Status: Pre-Release (v0.1.0-alpha) License: Apache-2.0 NPM Status: Public registry publication is pending; evaluate and build locally. 1. Core Architecture MCP Guardian operates as an interceptor middleware: ToolPermissionFence: Enforces granular Role-Based Access Control (RBAC) and explicit tool allowlists/denylists. InvocationSanitizer: Sanitizes parameter arguments, blocking directory traversal patterns (../) and dangerous system commands (sudo, rm -rf, chmod 777). RuntimeAuditLogger: Records every invocation payload, argument set, and permission verdict into a tamper-evident SHA-256 cryptographic hash chain. GuardianSandbox: Permission-gated execution wrapper evaluating authorization rules and logging audit records before dispatching to tool executors. 2. Implemented Capabilities & Test Verification Verified with hermetic unit tests: Permission Fencing: RBAC and denied command enforcement (tests/permission.test.ts). Audit Ledger: Cryptographic hash chain validation (tests/audit.test.ts). Execution Wrapper: Permission-gated dispatch and error containment (tests/sandbox.test.ts). Verification: 6/6 hermetic unit tests passing (0 failures). 3. Local Quick Start git clone https://github.com/alpallovy/ayeixa-mcp-guardian.git cd ayeixa-mcp-guardian npm ci npm run build npm test Usage Example import { GuardianSandbox, ToolPermissionFence, RuntimeAuditLogger } from './src'; const fence = new ToolPermissionFence({ allowedTools: ['read_file', 'list_dir'], blockedCommands: ['rm -rf', 'sudo', 'chmod 777'] }); const audit = new RuntimeAuditLogger(); const sandbox = new GuardianSandbox(fence, audit); const verdict = await sandbox.evaluateAndExecute({ toolName: 'read_file', arguments: { path: './src/index.ts' }, role: 'developer' }, async (args) => { return "File content safely read."; }); console.log("Allowed:", verdict.allowed); 4. Limitations & Contributing Pre-release v0.1.0-alpha. Provides application-level permission gating and parameter sanitization. Public npm publication is pending. We encourage security developers and researchers to contribute. See open good first issue tags on GitHub. License: Apache-2.0