diff --git a/src/lib/onboard/setup-nim-vllm.test.ts b/src/lib/onboard/setup-nim-vllm.test.ts
index 5041cfe56b8..a83fe7a746e 100644
--- a/src/lib/onboard/setup-nim-vllm.test.ts
+++ b/src/lib/onboard/setup-nim-vllm.test.ts
@@ -134,6 +134,62 @@ describe("setupNim vLLM route containment", () => {
     expect(renderedOutput).not.toContain("localhost:8000");
   });
 
+  it("authorizes a managed loopback endpoint without a trusted-private capability (#8539)", async () => {
+    const apiKey = "a".repeat(64);
+    const queryVllmModels = vi.fn(() => JSON.stringify({ data: [{ id: "served/model" }] }));
+    const validateOpenAiLikeSelection = vi.fn(async () => ({
+      ok: true,
+      api: "openai-completions",
+    }));
+    const handler = createSetupNimVllmHandler(
+      deps({
+        getLocalProviderBaseUrl: () => "http://127.0.0.1:8000/v1",
+        getLocalProviderValidationBaseUrl: () => "http://127.0.0.1:8000/v1",
+        getManagedVllmProviderBinding: () => ({
+          baseUrl: "http://127.0.0.1:8000/v1",
+          apiKey,
+        }),
+        queryVllmModels,
+        validateOpenAiLikeSelection,
+      }),
+    );
+
+    await expect(handler(state(null))).resolves.toBe("selected");
+    expect(validateOpenAiLikeSelection).toHaveBeenCalledWith(
+      "Local vLLM",
+      "http://127.0.0.1:8000/v1",
+      "served/model",
+      null,
+      undefined,
+      undefined,
+      { apiKey, pinnedAddresses: [], trustedPrivateCapability: undefined },
+    );
+  });
+
+  it("fails closed for a managed endpoint that is neither loopback nor operator-trusted private", async () => {
+    const queryVllmModels = vi.fn(() => JSON.stringify({ data: [{ id: "served/model" }] }));
+    const validateOpenAiLikeSelection = vi.fn(async () => ({ ok: true }));
+    const handler = createSetupNimVllmHandler(
+      deps({
+        getLocalProviderBaseUrl: () => "http://93.184.216.34:8000/v1",
+        getLocalProviderValidationBaseUrl: () => "http://93.184.216.34:8000/v1",
+        getManagedVllmProviderBinding: () => ({
+          baseUrl: "http://93.184.216.34:8000/v1",
+          apiKey: "a".repeat(64),
+        }),
+        queryVllmModels,
+        validateOpenAiLikeSelection,
+      }),
+    );
+
+    await expect(handler(state(null))).rejects.toThrow("exit 1");
+    expect(queryVllmModels).not.toHaveBeenCalled();
+    expect(validateOpenAiLikeSelection).not.toHaveBeenCalled();
+    expect(console.error).toHaveBeenCalledWith(
+      "  Managed vLLM endpoint authorization could not be verified.",
+    );
+  });
+
   it("rejects a root-matched alias with topology-neutral recovery for a managed dual endpoint", async () => {
     const selection = state("required/model");
     const validateOpenAiLikeSelection = vi.fn(async () => ({ ok: true }));
diff --git a/src/lib/onboard/setup-nim-vllm.ts b/src/lib/onboard/setup-nim-vllm.ts
index 4459c252146..5d276679342 100644
--- a/src/lib/onboard/setup-nim-vllm.ts
+++ b/src/lib/onboard/setup-nim-vllm.ts
@@ -3,9 +3,11 @@
 
 import {
   assertEndpointResolvesPublic,
+  isTrustedPrivateEndpointCapability,
   type TrustedPrivateEndpointCapability,
 } from "../inference/endpoint-ssrf-preflight";
 import { VLLM_MODELS } from "../inference/vllm-models";
+import { isLoopbackHostname } from "../private-networks";
 import { cliName } from "./branding";
 import type { SetupNimSelectionResult, SetupNimSelectionState } from "./setup-nim-flow";
 
@@ -77,7 +79,13 @@ async function managedVllmValidationOptions(baseUrl: string, apiKey: string) {
   const preflight = await assertEndpointResolvesPublic(baseUrl, undefined, {
     trustedPrivateHosts: [hostname],
   });
-  if (!preflight.ok || !preflight.trustedPrivateCapability) {
+  if (!preflight.ok) {
+    throw new Error("Managed vLLM endpoint authorization failed.");
+  }
+  if (
+    !isLoopbackHostname(hostname) &&
+    !isTrustedPrivateEndpointCapability(preflight.trustedPrivateCapability)
+  ) {
     throw new Error("Managed vLLM endpoint authorization failed.");
   }
   return {
@@ -263,6 +271,16 @@ export function createSetupNimVllmHandler(
         ? "  ✓ Using managed vLLM endpoint"
         : `  ✓ Using existing vLLM on localhost:${deps.VLLM_PORT}`,
     );
+    let managedValidationOptions: Awaited<ReturnType<typeof managedVllmValidationOptions>> | null =
+      null;
+    if (apiKey) {
+      try {
+        managedValidationOptions = await managedVllmValidationOptions(validationBaseUrl, apiKey);
+      } catch {
+        console.error("  Managed vLLM endpoint authorization could not be verified.");
+        deps.exitProcess(1);
+      }
+    }
     const raw = apiKey
       ? deps.queryVllmModels(validationBaseUrl, apiKey)
       : deps.runCapture(["curl", "-sf", `${validationBaseUrl}/models`], {
@@ -330,16 +348,6 @@ export function createSetupNimVllmHandler(
     }
 
     const validationModel = deps.requireValue(state.model, "Expected a detected vLLM model");
-    let managedValidationOptions: Awaited<ReturnType<typeof managedVllmValidationOptions>> | null =
-      null;
-    if (apiKey) {
-      try {
-        managedValidationOptions = await managedVllmValidationOptions(validationBaseUrl, apiKey);
-      } catch {
-        console.error("  Managed vLLM endpoint authorization could not be verified.");
-        deps.exitProcess(1);
-      }
-    }
     const validation = apiKey
       ? await deps.validateOpenAiLikeSelection(
           "Local vLLM",