diff --git a/extensions/synology-chat/src/webhook-handler.test.ts b/extensions/synology-chat/src/webhook-handler.test.ts
index a26a161de2d..7c78fbdb5e3 100644
--- a/extensions/synology-chat/src/webhook-handler.test.ts
+++ b/extensions/synology-chat/src/webhook-handler.test.ts
@@ -147,6 +147,125 @@ describe("createWebhookHandler", () => {
     expect(res._status).toBe(401);
   });
 
+  it("rate limits repeated invalid token guesses before the correct token can succeed", async () => {
+    const weakToken = "00000129";
+    const deliver = vi.fn().mockResolvedValue(null);
+    const handler = createWebhookHandler({
+      account: makeAccount({
+        accountId: "weak-token-bruteforce-" + Date.now(),
+        token: weakToken,
+        rateLimitPerMinute: 5,
+      }),
+      deliver,
+      log,
+    });
+
+    let guessedToken: string | null = null;
+    let saw429 = false;
+
+    for (let i = 0; i < 130; i += 1) {
+      const candidate = String(i).padStart(8, "0");
+      const req = makeReq(
+        "POST",
+        makeFormBody({
+          token: candidate,
+          user_id: "123",
+          username: "testuser",
+          text: "Hello bot",
+        }),
+      );
+      (req.socket as { remoteAddress?: string }).remoteAddress = "203.0.113.10";
+      const res = makeRes();
+      await handler(req, res);
+
+      if (res._status === 429) {
+        saw429 = true;
+        break;
+      }
+
+      if (res._status === 204) {
+        guessedToken = candidate;
+        break;
+      }
+
+      expect(res._status).toBe(401);
+    }
+
+    expect(saw429).toBe(true);
+    expect(guessedToken).toBeNull();
+    const lockedReq = makeReq(
+      "POST",
+      makeFormBody({
+        token: weakToken,
+        user_id: "123",
+        username: "testuser",
+        text: "Hello bot",
+      }),
+    );
+    (lockedReq.socket as { remoteAddress?: string }).remoteAddress = "203.0.113.10";
+    const lockedRes = makeRes();
+    await handler(lockedReq, lockedRes);
+
+    expect(lockedRes._status).toBe(429);
+    expect(deliver).not.toHaveBeenCalled();
+  });
+
+  it("keeps pre-auth throttling scoped to the remote IP", async () => {
+    const deliver = vi.fn().mockResolvedValue(null);
+    const handler = createWebhookHandler({
+      account: makeAccount({
+        accountId: "preauth-ip-scope-" + Date.now(),
+        rateLimitPerMinute: 1,
+      }),
+      deliver,
+      log,
+    });
+
+    const invalidReq = makeReq(
+      "POST",
+      makeFormBody({
+        token: "wrong-token",
+        user_id: "123",
+        username: "testuser",
+        text: "Hello",
+      }),
+    );
+    (invalidReq.socket as { remoteAddress?: string }).remoteAddress = "203.0.113.10";
+    const invalidRes = makeRes();
+    await handler(invalidReq, invalidRes);
+    expect(invalidRes._status).toBe(401);
+
+    const validReq = makeReq("POST", validBody);
+    (validReq.socket as { remoteAddress?: string }).remoteAddress = "203.0.113.11";
+    const validRes = makeRes();
+    await handler(validReq, validRes);
+
+    expect(validRes._status).toBe(204);
+    expect(deliver).toHaveBeenCalledTimes(1);
+  });
+
+  it("does not spend invalid-token budget on successful requests", async () => {
+    const deliver = vi.fn().mockResolvedValue(null);
+    const handler = createWebhookHandler({
+      account: makeAccount({
+        accountId: "invalid-token-budget-" + Date.now(),
+        rateLimitPerMinute: 30,
+      }),
+      deliver,
+      log,
+    });
+
+    for (let i = 0; i < 11; i += 1) {
+      const req = makeReq("POST", validBody);
+      (req.socket as { remoteAddress?: string }).remoteAddress = "203.0.113.20";
+      const res = makeRes();
+      await handler(req, res);
+      expect(res._status).toBe(204);
+    }
+
+    expect(deliver).toHaveBeenCalledTimes(11);
+  });
+
   it("accepts application/json with alias fields", async () => {
     const deliver = vi.fn().mockResolvedValue(null);
     const handler = createWebhookHandler({
diff --git a/extensions/synology-chat/src/webhook-handler.ts b/extensions/synology-chat/src/webhook-handler.ts
index d2c6427d993..5409c02b214 100644
--- a/extensions/synology-chat/src/webhook-handler.ts
+++ b/extensions/synology-chat/src/webhook-handler.ts
@@ -16,8 +16,77 @@ import type { SynologyWebhookPayload, ResolvedSynologyChatAccount } from "./type
 
 // One rate limiter per account, created lazily
 const rateLimiters = new Map<string, RateLimiter>();
+const invalidTokenRateLimiters = new Map<string, InvalidTokenRateLimiter>();
 const PREAUTH_MAX_BODY_BYTES = 64 * 1024;
 const PREAUTH_BODY_TIMEOUT_MS = 5_000;
+const PREAUTH_MAX_REQUESTS_PER_MINUTE = 10;
+const INVALID_TOKEN_WINDOW_MS = 60_000;
+const INVALID_TOKEN_MAX_TRACKED_KEYS = 5_000;
+
+type InvalidTokenRateLimitState = {
+  count: number;
+  windowStartMs: number;
+};
+
+class InvalidTokenRateLimiter {
+  private readonly limit: number;
+  private readonly state = new Map<string, InvalidTokenRateLimitState>();
+
+  constructor(limit: number) {
+    this.limit = limit;
+  }
+
+  private normalizeState(key: string, nowMs: number): InvalidTokenRateLimitState | undefined {
+    const existing = this.state.get(key);
+    if (!existing) {
+      return undefined;
+    }
+    if (nowMs - existing.windowStartMs >= INVALID_TOKEN_WINDOW_MS) {
+      this.state.delete(key);
+      return undefined;
+    }
+    return existing;
+  }
+
+  private touch(key: string, value: InvalidTokenRateLimitState): void {
+    this.state.delete(key);
+    this.state.set(key, value);
+    while (this.state.size > INVALID_TOKEN_MAX_TRACKED_KEYS) {
+      const oldestKey = this.state.keys().next().value;
+      if (!oldestKey) {
+        break;
+      }
+      this.state.delete(oldestKey);
+    }
+  }
+
+  isLocked(key: string, nowMs = Date.now()): boolean {
+    if (!key) {
+      return false;
+    }
+    const existing = this.normalizeState(key, nowMs);
+    return (existing?.count ?? 0) > this.limit;
+  }
+
+  recordFailure(key: string, nowMs = Date.now()): boolean {
+    if (!key) {
+      return false;
+    }
+    const existing = this.normalizeState(key, nowMs);
+    const nextCount = (existing?.count ?? 0) + 1;
+    const windowStartMs = existing?.windowStartMs ?? nowMs;
+    this.touch(key, { count: nextCount, windowStartMs });
+    return nextCount > this.limit;
+  }
+
+  clear(): void {
+    this.state.clear();
+  }
+
+  maxRequests(): number {
+    return this.limit;
+  }
+}
 
 function getRateLimiter(account: ResolvedSynologyChatAccount): RateLimiter {
   let rl = rateLimiters.get(account.accountId);
@@ -29,15 +98,34 @@ function getRateLimiter(account: ResolvedSynologyChatAccount): RateLimiter {
   return rl;
 }
 
+function getInvalidTokenRateLimiter(account: ResolvedSynologyChatAccount): InvalidTokenRateLimiter {
+  const limit = Math.min(account.rateLimitPerMinute, PREAUTH_MAX_REQUESTS_PER_MINUTE);
+  let rl = invalidTokenRateLimiters.get(account.accountId);
+  if (!rl || rl.maxRequests() !== limit) {
+    rl?.clear();
+    rl = new InvalidTokenRateLimiter(limit);
+    invalidTokenRateLimiters.set(account.accountId, rl);
+  }
+  return rl;
+}
+
 export function clearSynologyWebhookRateLimiterStateForTest(): void {
   for (const limiter of rateLimiters.values()) {
     limiter.clear();
   }
   rateLimiters.clear();
+  for (const limiter of invalidTokenRateLimiters.values()) {
+    limiter.clear();
+  }
+  invalidTokenRateLimiters.clear();
 }
 
 export function getSynologyWebhookRateLimiterCountForTest(): number {
-  return rateLimiters.size;
+  return rateLimiters.size + invalidTokenRateLimiters.size;
+}
+
+function getSynologyWebhookInvalidTokenRateLimitKey(req: IncomingMessage): string {
+  return req.socket?.remoteAddress ?? "unknown";
 }
 
 /** Read the full request body as a string. */
@@ -281,10 +369,22 @@ function authorizeSynologyWebhook(params: {
   req: IncomingMessage;
   account: ResolvedSynologyChatAccount;
   payload: SynologyWebhookPayload;
+  invalidTokenRateLimiter: InvalidTokenRateLimiter;
   rateLimiter: RateLimiter;
   log?: WebhookHandlerDeps["log"];
 }): SynologyWebhookAuthorization {
+  const invalidTokenRateLimitKey = getSynologyWebhookInvalidTokenRateLimitKey(params.req);
+  // Once a source has exhausted its invalid-token budget, reject all requests in the window.
+  if (params.invalidTokenRateLimiter.isLocked(invalidTokenRateLimitKey)) {
+    params.log?.warn(`Rate limit exceeded for remote IP: ${invalidTokenRateLimitKey}`);
+    return { ok: false, statusCode: 429, error: "Rate limit exceeded" };
+  }
+
   if (!validateToken(params.payload.token, params.account.token)) {
+    if (params.invalidTokenRateLimiter.recordFailure(invalidTokenRateLimitKey)) {
+      params.log?.warn(`Rate limit exceeded for remote IP: ${invalidTokenRateLimitKey}`);
+      return { ok: false, statusCode: 429, error: "Rate limit exceeded" };
+    }
     params.log?.warn(`Invalid token from ${params.req.socket?.remoteAddress}`);
     return { ok: false, statusCode: 401, error: "Invalid token" };
   }
@@ -313,6 +413,7 @@ function authorizeSynologyWebhook(params: {
   }
 
   if (!params.rateLimiter.check(params.payload.user_id)) {
+    // Keep a separate post-auth budget so authenticated users are still throttled per sender.
     params.log?.warn(`Rate limit exceeded for user: ${params.payload.user_id}`);
     return { ok: false, statusCode: 429, error: "Rate limit exceeded" };
   }
@@ -332,6 +433,7 @@ async function parseAndAuthorizeSynologyWebhook(params: {
   req: IncomingMessage;
   res: ServerResponse;
   account: ResolvedSynologyChatAccount;
+  invalidTokenRateLimiter: InvalidTokenRateLimiter;
   rateLimiter: RateLimiter;
   log?: WebhookHandlerDeps["log"];
 }): Promise<{ ok: false } | { ok: true; message: AuthorizedSynologyWebhook }> {
@@ -344,6 +446,7 @@ async function parseAndAuthorizeSynologyWebhook(params: {
     req: params.req,
     account: params.account,
     payload: parsed.payload,
+    invalidTokenRateLimiter: params.invalidTokenRateLimiter,
     rateLimiter: params.rateLimiter,
     log: params.log,
   });
@@ -453,6 +556,7 @@ async function processAuthorizedSynologyWebhook(params: {
 export function createWebhookHandler(deps: WebhookHandlerDeps) {
   const { account, deliver, log } = deps;
   const rateLimiter = getRateLimiter(account);
+  const invalidTokenRateLimiter = getInvalidTokenRateLimiter(account);
 
   return async (req: IncomingMessage, res: ServerResponse) => {
     // Only accept POST
@@ -464,6 +568,7 @@ export function createWebhookHandler(deps: WebhookHandlerDeps) {
       req,
       res,
       account,
+      invalidTokenRateLimiter,
       rateLimiter,
       log,
     });