diff --git a/packages/harness/src/extensions/posthog-provider/oauth.test.ts b/packages/harness/src/extensions/posthog-provider/oauth.test.ts
index 2a99b3c2b8..a26080fbee 100644
--- a/packages/harness/src/extensions/posthog-provider/oauth.test.ts
+++ b/packages/harness/src/extensions/posthog-provider/oauth.test.ts
@@ -77,6 +77,26 @@ function hitCallbackBody(port: number, query: string): Promise<string> {
   });
 }
 
+async function getAvailablePort(): Promise<number> {
+  const server = http.createServer();
+
+  await new Promise<void>((resolve, reject) => {
+    server.once("error", reject);
+    server.listen(0, "127.0.0.1", resolve);
+  });
+
+  const address = server.address();
+  if (address === null || typeof address === "string") {
+    throw new Error("Failed to allocate an OAuth callback port");
+  }
+
+  await new Promise<void>((resolve, reject) => {
+    server.close((error) => (error ? reject(error) : resolve()));
+  });
+
+  return address.port;
+}
+
 describe("buildAuthorizeUrl", () => {
   it("targets the same authorize endpoint and client as PostHog Code", () => {
     const url = buildAuthorizeUrl("us", "challenge123", getRedirectUri(8237));
@@ -151,8 +171,8 @@ describe("loginPosthog region selection", () => {
   let fetchSpy: MockInstance<typeof fetch>;
   let port: number;
 
-  beforeEach(() => {
-    port = 18500 + Math.floor(Math.random() * 500);
+  beforeEach(async () => {
+    port = await getAvailablePort();
     process.env.HARNESS_OAUTH_PORT = String(port);
     fetchSpy = vi.spyOn(global, "fetch").mockResolvedValue({
       ok: true,
@@ -256,8 +276,8 @@ describe("loginPosthog", { timeout: 15_000 }, () => {
   let fetchSpy: MockInstance<typeof fetch>;
   let port: number;
 
-  beforeEach(() => {
-    port = 18000 + Math.floor(Math.random() * 1000);
+  beforeEach(async () => {
+    port = await getAvailablePort();
     process.env.HARNESS_OAUTH_PORT = String(port);
     fetchSpy = vi.spyOn(global, "fetch");
   });
@@ -466,8 +486,8 @@ describe("openBrowser (via loginPosthog)", () => {
   let fetchSpy: MockInstance<typeof fetch>;
   let port: number;
 
-  beforeEach(() => {
-    port = 19000 + Math.floor(Math.random() * 1000);
+  beforeEach(async () => {
+    port = await getAvailablePort();
     process.env.HARNESS_OAUTH_PORT = String(port);
     fetchSpy = vi.spyOn(global, "fetch").mockResolvedValue({
       ok: true,
diff --git a/packages/ui/src/features/settings/sections/environments/useSandboxCustomImages.ts b/packages/ui/src/features/settings/sections/environments/useSandboxCustomImages.ts
index d87a90f588..c780e55b8d 100644
--- a/packages/ui/src/features/settings/sections/environments/useSandboxCustomImages.ts
+++ b/packages/ui/src/features/settings/sections/environments/useSandboxCustomImages.ts
@@ -7,9 +7,12 @@ import { useQueryClient } from "@tanstack/react-query";
 import { useAuthenticatedMutation } from "../../../../hooks/useAuthenticatedMutation";
 import { useAuthenticatedQuery } from "../../../../hooks/useAuthenticatedQuery";
 import { toast } from "../../../../primitives/toast";
+import { useFeatureFlag } from "../../../feature-flags/useFeatureFlag";
 import { watchImageBuild } from "./imageBuildWatcher";
 import { sandboxEnvKeys } from "./useSandboxEnvironments";
 
+const CUSTOM_IMAGES_FEATURE_FLAG = "tasks-modal-vm-sandbox";
+
 const sandboxCustomImageKeys = {
   list: ["sandbox-custom-images", "list"] as const,
   detail: (id: string) => ["sandbox-custom-images", "detail", id] as const,
@@ -30,6 +33,7 @@ export function useSandboxCustomImageDetail(imageId: string) {
 
 export function useSandboxCustomImages() {
   const queryClient = useQueryClient();
+  const customImagesFlagEnabled = useFeatureFlag(CUSTOM_IMAGES_FEATURE_FLAG);
 
   const {
     data: images,
@@ -39,6 +43,7 @@ export function useSandboxCustomImages() {
     sandboxCustomImageKeys.list,
     (client) => client.listSandboxCustomImages(),
     {
+      enabled: customImagesFlagEnabled,
       retry: (failureCount, error) =>
         !(error instanceof SandboxCustomImagesDisabledError) &&
         failureCount < 3,
@@ -56,7 +61,7 @@ export function useSandboxCustomImages() {
     },
   );
 
-  const customImagesEnabled = images !== undefined;
+  const customImagesEnabled = customImagesFlagEnabled && images !== undefined;
   const customImagesDisabled =
     error instanceof SandboxCustomImagesDisabledError;