diff --git a/docs/explanation/sessions-and-cookies.md b/docs/explanation/sessions-and-cookies.md
index 9beeb33a09..dacf9df18a 100644
--- a/docs/explanation/sessions-and-cookies.md
+++ b/docs/explanation/sessions-and-cookies.md
@@ -278,7 +278,7 @@ The `expires` argument to `createData` and `updateData` is the same `Date` at wh
 There are also several other session utilities available if you need them:
 
 - [`isSession`][is-session]
-- [`createMemorySessionStorage`][create-memory-session-storage]
+- [`createMemorySessionStorage`][create-memory-session-storage] (local dev and testing)
 - [`createSession`][create-session] (custom storage)
 - [`createFileSessionStorage`][create-file-session-storage] (node)
 - [`createWorkersKVSessionStorage`][create-workers-kv-session-storage] (Cloudflare Workers)
diff --git a/integration/rsc-csrf-action-test.ts b/integration/rsc-csrf-action-test.ts
new file mode 100644
index 0000000000..642fa2ff2c
--- /dev/null
+++ b/integration/rsc-csrf-action-test.ts
@@ -0,0 +1,169 @@
+import { test, expect, type Page } from "@playwright/test";
+import getPort from "get-port";
+
+import { PlaywrightFixture } from "./helpers/playwright-fixture.js";
+import {
+  createAppFixture,
+  createFixture,
+  js,
+} from "./helpers/create-fixture.js";
+import type { AppFixture, Fixture } from "./helpers/create-fixture.js";
+import { implementations, setupRscTest, validateRSCHtml } from "./rsc/utils.js";
+
+const csrfActionRoute = js`
+  let actionCalls = 0;
+
+  export function loader() {
+    return { actionCalls };
+  }
+
+  export async function action() {
+    actionCalls++;
+    return null;
+  }
+
+  export default function Component({ loaderData }) {
+    return (
+      <p data-action-calls={loaderData.actionCalls}>
+        Action calls: {loaderData.actionCalls}
+      </p>
+    );
+  }
+`;
+
+async function expectActionCalls(page: Page, count: string) {
+  await page.waitForSelector("[data-action-calls]");
+  expect(await page.locator("[data-action-calls]").textContent()).toContain(
+    `Action calls: ${count}`,
+  );
+  expect(
+    await page.locator("[data-action-calls]").getAttribute("data-action-calls"),
+  ).toBe(count);
+}
+
+test.describe("RSC CSRF action protection", () => {
+  test.describe("RSC Framework", () => {
+    let fixture: Fixture;
+    let appFixture: AppFixture | undefined;
+
+    test.beforeAll(async () => {
+      fixture = await createFixture({
+        templateName: "rsc-vite-framework",
+        files: {
+          "app/routes/csrf-action.tsx": csrfActionRoute,
+        },
+      });
+
+      appFixture = await createAppFixture(fixture);
+    });
+
+    test.afterAll(() => {
+      appFixture?.close();
+    });
+
+    test("does not call actions on cross-origin document POST requests", async ({
+      page,
+      request,
+    }) => {
+      let app = new PlaywrightFixture(appFixture!, page);
+
+      await app.goto("/csrf-action");
+      await expectActionCalls(page, "0");
+      validateRSCHtml(await page.content());
+
+      let response = await request.post(
+        `${appFixture!.serverUrl}/csrf-action`,
+        {
+          form: { intent: "mutate" },
+          headers: {
+            Origin: "https://attacker.example",
+          },
+        },
+      );
+      expect(response.status()).toBe(400);
+
+      await app.goto("/csrf-action");
+      await expectActionCalls(page, "0");
+    });
+  });
+
+  implementations.forEach((implementation) => {
+    test.describe(`RSC Data (${implementation.name})`, () => {
+      let port: number;
+      let stopAfterAll: () => void;
+
+      test.beforeAll(async () => {
+        port = await getPort();
+        stopAfterAll = await setupRscTest({
+          implementation,
+          port,
+          files: {
+            "src/routes.ts": js`
+              import type { unstable_RSCRouteConfig as RSCRouteConfig } from "react-router";
+
+              export const routes = [
+                {
+                  id: "root",
+                  path: "",
+                  lazy: () => import("./routes/root"),
+                  children: [
+                    {
+                      id: "csrf-action",
+                      path: "csrf-action",
+                      lazy: () => import("./routes/csrf-action"),
+                    },
+                  ],
+                },
+              ] satisfies RSCRouteConfig;
+            `,
+
+            "src/routes/root.tsx": js`
+              import { Outlet } from "react-router";
+
+              export function Layout({ children }: { children: React.ReactNode }) {
+                return (
+                  <html>
+                    <body>{children}</body>
+                  </html>
+                );
+              }
+
+              export default function RootRoute() {
+                return <Outlet />;
+              }
+            `,
+
+            "src/routes/csrf-action.tsx": csrfActionRoute,
+          },
+        });
+      });
+
+      test.afterAll(() => {
+        stopAfterAll?.();
+      });
+
+      test("does not call actions on cross-origin document POST requests", async ({
+        page,
+        request,
+      }) => {
+        await page.goto(`http://localhost:${port}/csrf-action`);
+        await expectActionCalls(page, "0");
+        validateRSCHtml(await page.content());
+
+        let response = await request.post(
+          `http://localhost:${port}/csrf-action`,
+          {
+            form: { intent: "mutate" },
+            headers: {
+              Origin: "https://attacker.example",
+            },
+          },
+        );
+        expect(response.status()).toBe(400);
+
+        await page.goto(`http://localhost:${port}/csrf-action`);
+        await expectActionCalls(page, "0");
+      });
+    });
+  });
+});
diff --git a/packages/react-router/.changes/patch.memory-session-random-uuid.md b/packages/react-router/.changes/patch.memory-session-random-uuid.md
new file mode 100644
index 0000000000..a201faead7
--- /dev/null
+++ b/packages/react-router/.changes/patch.memory-session-random-uuid.md
@@ -0,0 +1,3 @@
+Use `crypto.randomUUID()` for `createMemorySessionStorage` session ids
+
+- `createMemorySessionStorage` is only intended for local development and testing - sessions are lost when the server restarts
diff --git a/packages/react-router/.changes/patch.rsc-csrf.md b/packages/react-router/.changes/patch.rsc-csrf.md
new file mode 100644
index 0000000000..f778a415cf
--- /dev/null
+++ b/packages/react-router/.changes/patch.rsc-csrf.md
@@ -0,0 +1 @@
+Harden RSC CSRF codepaths.
diff --git a/packages/react-router/__tests__/server-runtime/sessions-test.ts b/packages/react-router/__tests__/server-runtime/sessions-test.ts
index dd8a1e15f4..41fef683f0 100644
--- a/packages/react-router/__tests__/server-runtime/sessions-test.ts
+++ b/packages/react-router/__tests__/server-runtime/sessions-test.ts
@@ -66,7 +66,7 @@ describe("In-memory session storage", () => {
     expect(session.get("user")).toEqual("mjackson");
   });
 
-  it("uses random hash keys as session ids", async () => {
+  it("uses random UUIDs as session ids", async () => {
     let { getSession, commitSession } = createMemorySessionStorage({
       cookie: { secrets: ["secret1"] },
     });
@@ -74,7 +74,7 @@ describe("In-memory session storage", () => {
     session.set("user", "mjackson");
     let setCookie = await commitSession(session);
     session = await getSession(getCookieFromSetCookie(setCookie));
-    expect(session.id).toMatch(/^[a-z0-9]{8}$/);
+    expect(session.id).toMatch(/^\w{8}-\w{4}-\w{4}-\w{4}-\w{12}$/);
   });
 });
 
diff --git a/packages/react-router/lib/rsc/server.rsc.ts b/packages/react-router/lib/rsc/server.rsc.ts
index 80cc86fa04..a7db3796e1 100644
--- a/packages/react-router/lib/rsc/server.rsc.ts
+++ b/packages/react-router/lib/rsc/server.rsc.ts
@@ -857,7 +857,17 @@ async function generateRenderResponse(
         if (isMutationMethod(request.method)) {
           try {
             throwIfPotentialCSRFAttack(request, allowedActionOrigins);
+          } catch (error) {
+            onError?.(error);
+            potentialCSRFAttackError = error;
+            request = new Request(request.url, {
+              method: "GET",
+              headers: request.headers,
+              signal: request.signal,
+            });
+          }
 
+          if (!potentialCSRFAttackError) {
             ctx.runningAction = true;
             let result = await processServerAction(
               request,
@@ -900,18 +910,12 @@ async function generateRenderResponse(
                 undefined,
               );
             }
-          } catch (error) {
-            potentialCSRFAttackError = error;
           }
         }
 
         let staticContext = await query(
           request,
-          skipRevalidation || !!potentialCSRFAttackError
-            ? {
-                filterMatchesToLoad: () => false,
-              }
-            : undefined,
+          skipRevalidation ? { filterMatchesToLoad: () => false } : undefined,
         );
 
         if (isResponse(staticContext)) {
diff --git a/packages/react-router/lib/server-runtime/sessions/memoryStorage.ts b/packages/react-router/lib/server-runtime/sessions/memoryStorage.ts
index efabc5fc99..d39ea62c7a 100644
--- a/packages/react-router/lib/server-runtime/sessions/memoryStorage.ts
+++ b/packages/react-router/lib/server-runtime/sessions/memoryStorage.ts
@@ -15,11 +15,10 @@ interface MemorySessionStorageOptions {
 }
 
 /**
- * Creates and returns a simple in-memory SessionStorage object, mostly useful
- * for testing and as a reference implementation.
+ * Creates and returns a simple in-memory SessionStorage object.
  *
- * Note: This storage does not scale beyond a single process, so it is not
- * suitable for most production scenarios.
+ * Intended for local development and testing. It does not scale beyond a single
+ * process, and all session data is lost when the server process stops/restarts.
  */
 export function createMemorySessionStorage<
   Data = SessionData,
@@ -36,7 +35,7 @@ export function createMemorySessionStorage<
   return createSessionStorage({
     cookie,
     async createData(data, expires) {
-      let id = Math.random().toString(36).substring(2, 10);
+      let id = crypto.randomUUID();
       map.set(id, { data, expires });
       return id;
     },