diff --git a/CHANGELOG.md b/CHANGELOG.md
index 21d78689220..60b08c0d0d8 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -13,6 +13,7 @@ Docs: https://docs.openclaw.ai
 
 ### Fixes
 
+- Security/Nextcloud Talk: drop replayed signed webhook events with persistent per-account replay dedupe across restarts, and reject unexpected webhook backend origins when account base URL is configured. Thanks @aristorechina for reporting.
 - Security/Nextcloud Talk: reject unsigned webhook traffic before full body reads, reducing unauthenticated request-body exposure, with auth-order regression coverage. (#26118) Thanks @bmendonca3.
 - Security/Nextcloud Talk: stop treating DM pairing-store entries as group allowlist senders, so group authorization remains bounded to configured group allowlists. (#26116) Thanks @bmendonca3.
 - Security/IRC: keep pairing-store approvals DM-only and out of IRC group allowlist authorization, with policy regression tests for allowlist resolution. (#26112) Thanks @bmendonca3.
diff --git a/extensions/nextcloud-talk/src/monitor.backend.test.ts b/extensions/nextcloud-talk/src/monitor.backend.test.ts
new file mode 100644
index 00000000000..9fb76093605
--- /dev/null
+++ b/extensions/nextcloud-talk/src/monitor.backend.test.ts
@@ -0,0 +1,91 @@
+import { type AddressInfo } from "node:net";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { createNextcloudTalkWebhookServer } from "./monitor.js";
+import { generateNextcloudTalkSignature } from "./signature.js";
+
+type WebhookHarness = {
+  webhookUrl: string;
+  stop: () => Promise<void>;
+};
+
+const cleanupFns: Array<() => Promise<void>> = [];
+
+afterEach(async () => {
+  while (cleanupFns.length > 0) {
+    const cleanup = cleanupFns.pop();
+    if (cleanup) {
+      await cleanup();
+    }
+  }
+});
+
+async function startWebhookServer(params: {
+  path: string;
+  isBackendAllowed: (backend: string) => boolean;
+  onMessage: () => void | Promise<void>;
+}): Promise<WebhookHarness> {
+  const { server, start } = createNextcloudTalkWebhookServer({
+    port: 0,
+    host: "127.0.0.1",
+    path: params.path,
+    secret: "nextcloud-secret",
+    isBackendAllowed: params.isBackendAllowed,
+    onMessage: params.onMessage,
+  });
+  await start();
+  const address = server.address() as AddressInfo | null;
+  if (!address) {
+    throw new Error("missing server address");
+  }
+  return {
+    webhookUrl: `http://127.0.0.1:${address.port}${params.path}`,
+    stop: () =>
+      new Promise<void>((resolve) => {
+        server.close(() => resolve());
+      }),
+  };
+}
+
+describe("createNextcloudTalkWebhookServer backend allowlist", () => {
+  it("rejects requests from unexpected backend origins", async () => {
+    const onMessage = vi.fn(async () => {});
+    const harness = await startWebhookServer({
+      path: "/nextcloud-backend-check",
+      isBackendAllowed: (backend) => backend === "https://nextcloud.expected",
+      onMessage,
+    });
+    cleanupFns.push(harness.stop);
+
+    const payload = {
+      type: "Create",
+      actor: { type: "Person", id: "alice", name: "Alice" },
+      object: {
+        type: "Note",
+        id: "msg-1",
+        name: "hello",
+        content: "hello",
+        mediaType: "text/plain",
+      },
+      target: { type: "Collection", id: "room-1", name: "Room 1" },
+    };
+    const body = JSON.stringify(payload);
+    const { random, signature } = generateNextcloudTalkSignature({
+      body,
+      secret: "nextcloud-secret",
+    });
+    const response = await fetch(harness.webhookUrl, {
+      method: "POST",
+      headers: {
+        "content-type": "application/json",
+        "x-nextcloud-talk-random": random,
+        "x-nextcloud-talk-signature": signature,
+        "x-nextcloud-talk-backend": "https://nextcloud.unexpected",
+      },
+      body,
+    });
+
+    expect(response.status).toBe(401);
+    expect(await response.json()).toEqual({ error: "Invalid backend" });
+    expect(onMessage).not.toHaveBeenCalled();
+  });
+});
diff --git a/extensions/nextcloud-talk/src/monitor.replay.test.ts b/extensions/nextcloud-talk/src/monitor.replay.test.ts
new file mode 100644
index 00000000000..9943b4b367d
--- /dev/null
+++ b/extensions/nextcloud-talk/src/monitor.replay.test.ts
@@ -0,0 +1,115 @@
+import { type AddressInfo } from "node:net";
+import { afterEach, describe, expect, it, vi } from "vitest";
+import { createNextcloudTalkWebhookServer } from "./monitor.js";
+import { generateNextcloudTalkSignature } from "./signature.js";
+
+type WebhookHarness = {
+  webhookUrl: string;
+  stop: () => Promise<void>;
+};
+
+const cleanupFns: Array<() => Promise<void>> = [];
+
+afterEach(async () => {
+  while (cleanupFns.length > 0) {
+    const cleanup = cleanupFns.pop();
+    if (cleanup) {
+      await cleanup();
+    }
+  }
+});
+
+async function startWebhookServer(params: {
+  path: string;
+  shouldProcessMessage?: (
+    message: Parameters<
+      NonNullable<Parameters<typeof createNextcloudTalkWebhookServer>[0]["onMessage"]>
+    >[0],
+  ) => boolean | Promise<boolean>;
+  onMessage: (message: { messageId: string }) => void | Promise<void>;
+}): Promise<WebhookHarness> {
+  const { server, start } = createNextcloudTalkWebhookServer({
+    port: 0,
+    host: "127.0.0.1",
+    path: params.path,
+    secret: "nextcloud-secret",
+    shouldProcessMessage: params.shouldProcessMessage,
+    onMessage: params.onMessage,
+  });
+  await start();
+  const address = server.address() as AddressInfo | null;
+  if (!address) {
+    throw new Error("missing server address");
+  }
+  return {
+    webhookUrl: `http://127.0.0.1:${address.port}${params.path}`,
+    stop: () =>
+      new Promise<void>((resolve) => {
+        server.close(() => resolve());
+      }),
+  };
+}
+
+function createSignedRequest(body: string): { random: string; signature: string } {
+  return generateNextcloudTalkSignature({
+    body,
+    secret: "nextcloud-secret",
+  });
+}
+
+describe("createNextcloudTalkWebhookServer replay handling", () => {
+  it("acknowledges replayed requests and skips onMessage side effects", async () => {
+    const seen = new Set<string>();
+    const onMessage = vi.fn(async () => {});
+    const shouldProcessMessage = vi.fn(async (message: { messageId: string }) => {
+      if (seen.has(message.messageId)) {
+        return false;
+      }
+      seen.add(message.messageId);
+      return true;
+    });
+    const harness = await startWebhookServer({
+      path: "/nextcloud-replay",
+      shouldProcessMessage,
+      onMessage,
+    });
+    cleanupFns.push(harness.stop);
+
+    const payload = {
+      type: "Create",
+      actor: { type: "Person", id: "alice", name: "Alice" },
+      object: {
+        type: "Note",
+        id: "msg-1",
+        name: "hello",
+        content: "hello",
+        mediaType: "text/plain",
+      },
+      target: { type: "Collection", id: "room-1", name: "Room 1" },
+    };
+    const body = JSON.stringify(payload);
+    const { random, signature } = createSignedRequest(body);
+    const headers = {
+      "content-type": "application/json",
+      "x-nextcloud-talk-random": random,
+      "x-nextcloud-talk-signature": signature,
+      "x-nextcloud-talk-backend": "https://nextcloud.example",
+    };
+
+    const first = await fetch(harness.webhookUrl, {
+      method: "POST",
+      headers,
+      body,
+    });
+    const second = await fetch(harness.webhookUrl, {
+      method: "POST",
+      headers,
+      body,
+    });
+
+    expect(first.status).toBe(200);
+    expect(second.status).toBe(200);
+    expect(shouldProcessMessage).toHaveBeenCalledTimes(2);
+    expect(onMessage).toHaveBeenCalledTimes(1);
+  });
+});
diff --git a/extensions/nextcloud-talk/src/monitor.ts b/extensions/nextcloud-talk/src/monitor.ts
index 4b68a3c4d0b..0408070c4a4 100644
--- a/extensions/nextcloud-talk/src/monitor.ts
+++ b/extensions/nextcloud-talk/src/monitor.ts
@@ -1,4 +1,5 @@
 import { createServer, type IncomingMessage, type Server, type ServerResponse } from "node:http";
+import os from "node:os";
 import {
   createLoggerBackedRuntime,
   type RuntimeEnv,
@@ -8,6 +9,7 @@ import {
 } from "openclaw/plugin-sdk";
 import { resolveNextcloudTalkAccount } from "./accounts.js";
 import { handleNextcloudTalkInbound } from "./inbound.js";
+import { createNextcloudTalkReplayGuard } from "./replay-guard.js";
 import { getNextcloudTalkRuntime } from "./runtime.js";
 import { extractNextcloudTalkHeaders, verifyNextcloudTalkSignature } from "./signature.js";
 import type {
@@ -31,6 +33,14 @@ function formatError(err: unknown): string {
   return typeof err === "string" ? err : JSON.stringify(err);
 }
 
+function normalizeOrigin(value: string): string | null {
+  try {
+    return new URL(value).origin.toLowerCase();
+  } catch {
+    return null;
+  }
+}
+
 function parseWebhookPayload(body: string): NextcloudTalkWebhookPayload | null {
   try {
     const data = JSON.parse(body);
@@ -93,6 +103,8 @@ export function createNextcloudTalkWebhookServer(opts: NextcloudTalkWebhookServe
       ? Math.floor(opts.maxBodyBytes)
       : DEFAULT_WEBHOOK_MAX_BODY_BYTES;
   const readBody = opts.readBody ?? readNextcloudTalkWebhookBody;
+  const isBackendAllowed = opts.isBackendAllowed;
+  const shouldProcessMessage = opts.shouldProcessMessage;
 
   const server = createServer(async (req: IncomingMessage, res: ServerResponse) => {
     if (req.url === HEALTH_PATH) {
@@ -116,6 +128,11 @@ export function createNextcloudTalkWebhookServer(opts: NextcloudTalkWebhookServe
         res.end(JSON.stringify({ error: "Missing signature headers" }));
         return;
       }
+      if (isBackendAllowed && !isBackendAllowed(headers.backend)) {
+        res.writeHead(401, { "Content-Type": "application/json" });
+        res.end(JSON.stringify({ error: "Invalid backend" }));
+        return;
+      }
 
       const body = await readBody(req, maxBodyBytes);
 
@@ -146,6 +163,14 @@ export function createNextcloudTalkWebhookServer(opts: NextcloudTalkWebhookServe
       }
 
       const message = payloadToInboundMessage(payload);
+      if (shouldProcessMessage) {
+        const shouldProcess = await shouldProcessMessage(message);
+        if (!shouldProcess) {
+          res.writeHead(200);
+          res.end();
+          return;
+        }
+      }
 
       res.writeHead(200);
       res.end();
@@ -233,12 +258,41 @@ export async function monitorNextcloudTalkProvider(
     channel: "nextcloud-talk",
     accountId: account.accountId,
   });
+  const expectedBackendOrigin = normalizeOrigin(account.baseUrl);
+  const replayGuard = createNextcloudTalkReplayGuard({
+    stateDir: core.state.resolveStateDir(process.env, os.homedir),
+    onDiskError: (error) => {
+      logger.warn(
+        `[nextcloud-talk:${account.accountId}] replay guard disk error: ${String(error)}`,
+      );
+    },
+  });
 
   const { start, stop } = createNextcloudTalkWebhookServer({
     port,
     host,
     path,
     secret: account.secret,
+    isBackendAllowed: (backend) => {
+      if (!expectedBackendOrigin) {
+        return true;
+      }
+      const backendOrigin = normalizeOrigin(backend);
+      return backendOrigin === expectedBackendOrigin;
+    },
+    shouldProcessMessage: async (message) => {
+      const shouldProcess = await replayGuard.shouldProcessMessage({
+        accountId: account.accountId,
+        roomToken: message.roomToken,
+        messageId: message.messageId,
+      });
+      if (!shouldProcess) {
+        logger.warn(
+          `[nextcloud-talk:${account.accountId}] replayed webhook ignored room=${message.roomToken} messageId=${message.messageId}`,
+        );
+      }
+      return shouldProcess;
+    },
     onMessage: async (message) => {
       core.channel.activity.record({
         channel: "nextcloud-talk",
diff --git a/extensions/nextcloud-talk/src/replay-guard.test.ts b/extensions/nextcloud-talk/src/replay-guard.test.ts
new file mode 100644
index 00000000000..0bf18acb600
--- /dev/null
+++ b/extensions/nextcloud-talk/src/replay-guard.test.ts
@@ -0,0 +1,70 @@
+import { mkdtemp, rm } from "node:fs/promises";
+import os from "node:os";
+import path from "node:path";
+import { afterEach, describe, expect, it } from "vitest";
+import { createNextcloudTalkReplayGuard } from "./replay-guard.js";
+
+const tempDirs: string[] = [];
+
+afterEach(async () => {
+  while (tempDirs.length > 0) {
+    const dir = tempDirs.pop();
+    if (dir) {
+      await rm(dir, { recursive: true, force: true });
+    }
+  }
+});
+
+async function makeTempDir(): Promise<string> {
+  const dir = await mkdtemp(path.join(os.tmpdir(), "nextcloud-talk-replay-"));
+  tempDirs.push(dir);
+  return dir;
+}
+
+describe("createNextcloudTalkReplayGuard", () => {
+  it("persists replay decisions across guard instances", async () => {
+    const stateDir = await makeTempDir();
+
+    const firstGuard = createNextcloudTalkReplayGuard({ stateDir });
+    const firstAttempt = await firstGuard.shouldProcessMessage({
+      accountId: "account-a",
+      roomToken: "room-1",
+      messageId: "msg-1",
+    });
+    const replayAttempt = await firstGuard.shouldProcessMessage({
+      accountId: "account-a",
+      roomToken: "room-1",
+      messageId: "msg-1",
+    });
+
+    const secondGuard = createNextcloudTalkReplayGuard({ stateDir });
+    const restartReplayAttempt = await secondGuard.shouldProcessMessage({
+      accountId: "account-a",
+      roomToken: "room-1",
+      messageId: "msg-1",
+    });
+
+    expect(firstAttempt).toBe(true);
+    expect(replayAttempt).toBe(false);
+    expect(restartReplayAttempt).toBe(false);
+  });
+
+  it("scopes replay state by account namespace", async () => {
+    const stateDir = await makeTempDir();
+    const guard = createNextcloudTalkReplayGuard({ stateDir });
+
+    const accountAFirst = await guard.shouldProcessMessage({
+      accountId: "account-a",
+      roomToken: "room-1",
+      messageId: "msg-9",
+    });
+    const accountBFirst = await guard.shouldProcessMessage({
+      accountId: "account-b",
+      roomToken: "room-1",
+      messageId: "msg-9",
+    });
+
+    expect(accountAFirst).toBe(true);
+    expect(accountBFirst).toBe(true);
+  });
+});
diff --git a/extensions/nextcloud-talk/src/replay-guard.ts b/extensions/nextcloud-talk/src/replay-guard.ts
new file mode 100644
index 00000000000..14b074ed2ab
--- /dev/null
+++ b/extensions/nextcloud-talk/src/replay-guard.ts
@@ -0,0 +1,65 @@
+import path from "node:path";
+import { createPersistentDedupe } from "openclaw/plugin-sdk";
+
+const DEFAULT_REPLAY_TTL_MS = 24 * 60 * 60 * 1000;
+const DEFAULT_MEMORY_MAX_SIZE = 1_000;
+const DEFAULT_FILE_MAX_ENTRIES = 10_000;
+
+function sanitizeSegment(value: string): string {
+  const trimmed = value.trim();
+  if (!trimmed) {
+    return "default";
+  }
+  return trimmed.replace(/[^a-zA-Z0-9_-]/g, "_");
+}
+
+function buildReplayKey(params: { roomToken: string; messageId: string }): string | null {
+  const roomToken = params.roomToken.trim();
+  const messageId = params.messageId.trim();
+  if (!roomToken || !messageId) {
+    return null;
+  }
+  return `${roomToken}:${messageId}`;
+}
+
+export type NextcloudTalkReplayGuardOptions = {
+  stateDir: string;
+  ttlMs?: number;
+  memoryMaxSize?: number;
+  fileMaxEntries?: number;
+  onDiskError?: (error: unknown) => void;
+};
+
+export type NextcloudTalkReplayGuard = {
+  shouldProcessMessage: (params: {
+    accountId: string;
+    roomToken: string;
+    messageId: string;
+  }) => Promise<boolean>;
+};
+
+export function createNextcloudTalkReplayGuard(
+  options: NextcloudTalkReplayGuardOptions,
+): NextcloudTalkReplayGuard {
+  const stateDir = options.stateDir.trim();
+  const persistentDedupe = createPersistentDedupe({
+    ttlMs: options.ttlMs ?? DEFAULT_REPLAY_TTL_MS,
+    memoryMaxSize: options.memoryMaxSize ?? DEFAULT_MEMORY_MAX_SIZE,
+    fileMaxEntries: options.fileMaxEntries ?? DEFAULT_FILE_MAX_ENTRIES,
+    resolveFilePath: (namespace) =>
+      path.join(stateDir, "nextcloud-talk", "replay-dedupe", `${sanitizeSegment(namespace)}.json`),
+  });
+
+  return {
+    shouldProcessMessage: async ({ accountId, roomToken, messageId }) => {
+      const replayKey = buildReplayKey({ roomToken, messageId });
+      if (!replayKey) {
+        return true;
+      }
+      return await persistentDedupe.checkAndRecord(replayKey, {
+        namespace: accountId,
+        onDiskError: options.onDiskError,
+      });
+    },
+  };
+}
diff --git a/extensions/nextcloud-talk/src/types.ts b/extensions/nextcloud-talk/src/types.ts
index a9fe49be36d..e7af64a965c 100644
--- a/extensions/nextcloud-talk/src/types.ts
+++ b/extensions/nextcloud-talk/src/types.ts
@@ -170,6 +170,8 @@ export type NextcloudTalkWebhookServerOptions = {
   secret: string;
   maxBodyBytes?: number;
   readBody?: (req: import("node:http").IncomingMessage, maxBodyBytes: number) => Promise<string>;
+  isBackendAllowed?: (backend: string) => boolean;
+  shouldProcessMessage?: (message: NextcloudTalkInboundMessage) => boolean | Promise<boolean>;
   onMessage: (message: NextcloudTalkInboundMessage) => void | Promise<void>;
   onError?: (error: Error) => void;
   abortSignal?: AbortSignal;