fix(connection): fence every /api request behind one browser-trust check

The only browser-trust guard covered host.pickDirectory, while the consequential methods (session.prompt drives bash) accepted any Host — open to DNS rebinding, where a rebound page reads and writes the API as if same-origin and only the Host header betrays the attacker's domain. The pickDirectory-specific loopback guard becomes a prefix-wide fence: Host must be loopback or an exact host[:port] from the new trustedHosts config, an attached Origin must equal that authority, and explicit cross-site markers are refused; requests without browser markers (curl, tests, native clients) pass, because without a browser there is no confused deputy. The loopback-socket check is dropped — binding policy expresses reachability, and the fence is not an auth layer. The Agent Note records the full threat model and the alternatives.
2026-07-28 14:56:45 +08:00
parent d2fea6d789
commit 01d68dee4e
18 changed files with 339 additions and 160 deletions
@@ -0,0 +1,71 @@
+/**
+ * Browser-trust fence for every /api request. Defends the two confused-deputy
+ * paths a browser opens against a local HTTP API — DNS rebinding (Host names
+ * the attacker's domain while the socket reaches this server) and cross-site
+ * requests fired from a malicious page — without blocking non-browser clients
+ * (no browser markers → no deputy to confuse) or legitimately remote browsers
+ * (their authority is declared via `trustedHosts`). Network reachability and
+ * authentication stay out of scope: binding policy belongs to the webserver
+ * config, and this fence is not an auth layer.
+ */
+
+import type { IncomingHttpHeaders } from 'node:http'
+
+/** The request facts the fence reads (structural subset of IncomingMessage). */
+interface ApiTrustRequest {
+  headers: IncomingHttpHeaders
+}
+
+function header(headers: IncomingHttpHeaders, name: string): string | undefined {
+  const value = headers[name]
+  return typeof value === 'string' ? value : undefined
+}
+
+function isLoopbackHostname(hostname: string): boolean {
+  if (hostname === 'localhost' || hostname === '[::1]') return true
+  const parts = hostname.split('.')
+  return parts.length === 4
+    && parts[0] === '127'
+    && parts.every(part => /^\d{1,3}$/.test(part) && Number(part) <= 255)
+}
+
+/** Hostname of a Host-header authority (port stripped, lowercased, IPv6 bracketed), or undefined when unparsable. */
+function authorityHostname(authority: string): string | undefined {
+  try {
+    // http: is a WHATWG "special scheme": parsing yields a non-empty hostname or throws.
+    return new URL(`http://${authority}`).hostname
+  } catch {
+    return undefined
+  }
+}
+
+/**
+ * Decide whether one /api request may reach the RPC bridge.
+ * @param request - node HTTP request facts (headers).
+ * @param trustedHosts - exact non-loopback `host[:port]` authorities this deployment serves.
+ * @returns true when the Host is ours and any browser markers are same-origin.
+ */
+export function isTrustedApiRequest(request: ApiTrustRequest, trustedHosts: readonly string[]): boolean {
+  // Host fence (DNS-rebinding defense): the browser fills Host from the URL it
+  // believes it is talking to, so a rebound page carries the attacker's domain
+  // here even though the socket lands on this server.
+  const host = header(request.headers, 'host')
+  if (host === undefined) return false
+  const hostname = authorityHostname(host)
+  if (hostname === undefined) return false
+  if (!isLoopbackHostname(hostname) && !trustedHosts.includes(host)) return false
+  // Cross-site fence: modern browsers label the initiator relationship on
+  // every fetch; an explicit cross-site marker is refused regardless of Origin.
+  if (header(request.headers, 'sec-fetch-site') === 'cross-site') return false
+  // Origin fence: when a browser attaches an Origin it must be exactly this
+  // authority. Absent Origin = non-browser client (curl, tests, native shells)
+  // — allowed, because without a browser there is no confused deputy. The
+  // literal "null" (sandboxed iframes, file: pages) is an opaque origin, refused.
+  const origin = header(request.headers, 'origin')
+  if (origin === undefined) return true
+  try {
+    return new URL(origin).host === host
+  } catch {
+    return false
+  }
+}
@@ -1,11 +1,12 @@
 /** Host HTTP bridge for browser-client RPC. */
 import type { Context } from 'cordis'
+import z from 'schemastery'
 // Activates the httpServer Context merge used below.
 import type { WebRoute } from '@deepseek-ai/dsh-host-webserver'
 import { toFetchHandler } from '@deepseek-ai/dsh-host-apiproxy'
 import { API_PATH } from './api-path.ts'
 import { bridge } from './http-bridge.ts'
-import { isTrustedNativeDialogRequest } from './native-dialog-request.ts'
+import { isTrustedApiRequest } from './api-request-trust.ts'

 export { API_PATH } from './api-path.ts'

@@ -15,19 +16,37 @@ export const name = 'client-connection'
 /** Services required before mounting the route. */
 export const inject = ['httpServer', 'apiProxy']

+/** Plugin config: the deployment's non-loopback serving authorities. */
+export interface ConnectionConfig {
+  /**
+   * Exact `host[:port]` authorities this deployment serves beyond loopback.
+   * The /api trust fence refuses any request whose Host is neither loopback
+   * nor listed here, so a non-loopback (`0.0.0.0`) deployment must declare
+   * the names it is reached by.
+   */
+  trustedHosts?: string[]
+}
+
+export const Config: z<ConnectionConfig> = z.object({
+  trustedHosts: z.array(String).default([]),
+})
+
 /**
- * Mounts the API gateway under the browser transport prefix.
+ * Mounts the API gateway under the browser transport prefix. Every request on
+ * the prefix passes the browser-trust fence first (DNS-rebinding and
+ * cross-site defense — [api-request-trust](./api-request-trust.ts)).
 * @param ctx - Host plugin context.
+ * @param config - resolved plugin config (schema defaults applied).
 */
-export function apply(ctx: Context): void {
+export function apply(ctx: Context, config?: ConnectionConfig): void {
+  // The Loader resolves schema defaults; hand-built test contexts may pass none.
+  const trustedHosts = config?.trustedHosts ?? []
  const apiHandler = toFetchHandler(ctx.apiProxy)
  const route: WebRoute = {
    kind: 'prefix',
    path: API_PATH,
    handler: async (req, res) => {
-      const pathname = new URL(req.url ?? '/', 'http://dsh.internal').pathname
-      if (pathname === `${API_PATH}/host.pickDirectory`
-        && !isTrustedNativeDialogRequest(req)) {
+      if (!isTrustedApiRequest(req, trustedHosts)) {
        res.writeHead(403)
        res.end('forbidden')
        return
@@ -1,52 +0,0 @@
-/** Trust check for browser requests that can open an operating-system dialog. */
-
-import type { IncomingHttpHeaders } from 'node:http'
-
-interface NativeDialogRequest {
-  headers: IncomingHttpHeaders
-  socket: { remoteAddress?: string | undefined }
-}
-
-function header(headers: IncomingHttpHeaders, name: string): string | undefined {
-  const value = headers[name]
-  return typeof value === 'string' ? value : undefined
-}
-
-function isLoopback(address: string | undefined): boolean {
-  if (address === undefined) return false
-  if (address === '::1') return true
-  const ipv4 = address.startsWith('::ffff:') ? address.slice('::ffff:'.length) : address
-  const first = ipv4.split('.')[0]
-  return first === '127'
-}
-
-function isLoopbackHostname(hostname: string): boolean {
-  if (hostname === 'localhost' || hostname === '[::1]' || hostname === '::1') return true
-  const parts = hostname.split('.')
-  return parts.length === 4
-    && parts[0] === '127'
-    && parts.every(part => /^\d{1,3}$/.test(part) && Number(part) <= 255)
-}
-
-/**
- * Require a local socket plus browser-controlled same-origin metadata.
- * @param request - the node HTTP request facts used by the carrier guard.
- * @returns true only for a same-origin browser request whose peer and URL are loopback.
- */
-export function isTrustedNativeDialogRequest(request: NativeDialogRequest): boolean {
-  if (!isLoopback(request.socket.remoteAddress)) return false
-  if (header(request.headers, 'sec-fetch-site') !== 'same-origin') return false
-  const origin = header(request.headers, 'origin')
-  const host = header(request.headers, 'host')
-  if (origin === undefined || host === undefined) return false
-  try {
-    const parsed = new URL(origin)
-    const hostUrl = new URL(`http://${host}`)
-    return (parsed.protocol === 'http:' || parsed.protocol === 'https:')
-      && parsed.host === host
-      && isLoopbackHostname(parsed.hostname)
-      && isLoopbackHostname(hostUrl.hostname)
-  } catch {
-    return false
-  }
-}