9Router is an AI router & token saver. Prior to 0.5.2, 9router determines whether a /v1 LLM proxy request is local by reading the client-controlled Host header, allowing a remote unauthenticated attacker to send Host: localhost and bypass API-key authentication. In the default configuration, this exposes the /v1 proxy to upstream provider calls using stored provider credentials and allows /v1/search with the searxng provider_options.baseUrl parameter to drive server-side requests to internal or cloud-metadata hosts. This issue is fixed in version 0.5.2.

Affected: npm: 9router

## Summary

9router's request guard decides a request is "local" (and therefore exempt from API-key auth on the `/v1` LLM proxy) by reading the **client-controlled `Host` header**. Because 9router binds `0.0.0.0` by default (and the CLI misleadingly prints "localhost"), a remote, unauthenticated attacker who can reach the port can send `Host: localhost` to be treated as local and obtain `/v1` proxy access with **no API key, no CLI token, and no dashboard login**. In the default configuration (`requireApiKey` is absent from `DEFAULT_SETTINGS`, so the handler-side key check is skipped), this yields:

- **Open AI relay** — the proxy forwards the attacker's requests to AI providers using the **victim's stored paid API keys** (cost/quota theft, prompt-based data exfiltration through the victim's accounts). - **Unauthenticated SSRF** — `/v1/search` with the built-in `noAuth` `searxng` provider takes its outbound fetch URL from the request body (`provider_options.baseUrl`), so the attacker drives a server-side fetch to any internal/cloud-metadata host and gets the JSON response reflected back.

- **Affected:** `9router <= 0.4.80` (current), `src/dashboardGuard.js` (`isLocalRequest`), `src/sse/handlers/{chat,search}.js`, `src/lib/db/repos/settingsRepo.js`, `cli/cli.js`. - **Distinct from** the existing advisories GHSA-fhh6-4qxv-rpqj (MCP-plugin RCE, patched) and GHSA-xrrh-p7f2-27vm (legacy `<0.3.75` authz bypass).

## Details

### The bypass (`src/dashboardGuard.js`) ```js function…