diff --git a/CHANGELOG.md b/CHANGELOG.md
index fcf8d4862d8..48290d3389f 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -14,6 +14,7 @@ Docs: https://docs.openclaw.ai
 
 ### Fixes
 
+- Telegram/webhook auth: validate the Telegram webhook secret before reading or parsing request bodies, so unauthenticated requests are rejected immediately instead of consuming up to 1 MB first. Thanks @space08.
 - Build/plugin-sdk bundling: bundle plugin-sdk subpath entries in one shared build pass so published packages stop duplicating shared chunks and avoid the recent plugin-sdk memory blow-up. (#45426) Thanks @TarasShyn.
 - Browser/existing-session: accept text-only `list_pages` and `new_page` responses from Chrome DevTools MCP so live-session tab discovery and new-tab open flows keep working when the server omits structured page metadata.
 - Ollama/reasoning visibility: stop promoting native `thinking` and `reasoning` fields into final assistant text so local reasoning models no longer leak internal thoughts in normal replies. (#45330) Thanks @xi7ang.
diff --git a/src/telegram/webhook.test.ts b/src/telegram/webhook.test.ts
index 1b630b034df..0f2736a30b9 100644
--- a/src/telegram/webhook.test.ts
+++ b/src/telegram/webhook.test.ts
@@ -88,6 +88,70 @@ async function postWebhookJson(params: {
   );
 }
 
+async function postWebhookHeadersOnly(params: {
+  port: number;
+  path: string;
+  declaredLength: number;
+  secret?: string;
+  timeoutMs?: number;
+}): Promise<{ statusCode: number; body: string }> {
+  return await new Promise((resolve, reject) => {
+    let settled = false;
+    const finishResolve = (value: { statusCode: number; body: string }) => {
+      if (settled) {
+        return;
+      }
+      settled = true;
+      clearTimeout(timeout);
+      resolve(value);
+    };
+    const finishReject = (error: unknown) => {
+      if (settled) {
+        return;
+      }
+      settled = true;
+      clearTimeout(timeout);
+      reject(error);
+    };
+
+    const req = request(
+      {
+        hostname: "127.0.0.1",
+        port: params.port,
+        path: params.path,
+        method: "POST",
+        headers: {
+          "content-type": "application/json",
+          "content-length": String(params.declaredLength),
+          ...(params.secret ? { "x-telegram-bot-api-secret-token": params.secret } : {}),
+        },
+      },
+      (res) => {
+        collectResponseBody(res, (payload) => {
+          finishResolve(payload);
+          req.destroy();
+        });
+      },
+    );
+
+    const timeout = setTimeout(() => {
+      req.destroy(
+        new Error(`webhook header-only post timed out after ${params.timeoutMs ?? 5_000}ms`),
+      );
+      finishReject(new Error("timed out waiting for webhook response"));
+    }, params.timeoutMs ?? 5_000);
+
+    req.on("error", (error) => {
+      if (settled && (error as NodeJS.ErrnoException).code === "ECONNRESET") {
+        return;
+      }
+      finishReject(error);
+    });
+
+    req.flushHeaders();
+  });
+}
+
 function createDeterministicRng(seed: number): () => number {
   let state = seed >>> 0;
   return () => {
@@ -399,7 +463,34 @@ describe("startTelegramWebhook", () => {
           secret: TELEGRAM_SECRET,
         });
         expect(response.status).toBe(200);
-        expect(handlerSpy).toHaveBeenCalled();
+        expect(handlerSpy).toHaveBeenCalledWith(
+          JSON.parse(payload),
+          expect.any(Function),
+          TELEGRAM_SECRET,
+          expect.any(Function),
+        );
+      },
+    );
+  });
+
+  it("rejects unauthenticated requests before reading the request body", async () => {
+    handlerSpy.mockClear();
+    await withStartedWebhook(
+      {
+        secret: TELEGRAM_SECRET,
+        path: TELEGRAM_WEBHOOK_PATH,
+      },
+      async ({ port }) => {
+        const response = await postWebhookHeadersOnly({
+          port,
+          path: TELEGRAM_WEBHOOK_PATH,
+          declaredLength: 1_024 * 1_024,
+          secret: "wrong-secret",
+        });
+
+        expect(response.statusCode).toBe(401);
+        expect(response.body).toBe("unauthorized");
+        expect(handlerSpy).not.toHaveBeenCalled();
       },
     );
   });
diff --git a/src/telegram/webhook.ts b/src/telegram/webhook.ts
index 1de38b1bb36..c049089a2ad 100644
--- a/src/telegram/webhook.ts
+++ b/src/telegram/webhook.ts
@@ -1,3 +1,4 @@
+import { timingSafeEqual } from "node:crypto";
 import { createServer } from "node:http";
 import { InputFile, webhookCallback } from "grammy";
 import type { OpenClawConfig } from "../config/config.js";
@@ -74,6 +75,28 @@ async function initializeTelegramWebhookBot(params: {
   });
 }
 
+function resolveSingleHeaderValue(header: string | string[] | undefined): string | undefined {
+  if (typeof header === "string") {
+    return header;
+  }
+  if (Array.isArray(header) && header.length === 1) {
+    return header[0];
+  }
+  return undefined;
+}
+
+function hasValidTelegramWebhookSecret(
+  secretHeader: string | undefined,
+  expectedSecret: string,
+): boolean {
+  if (typeof secretHeader !== "string") {
+    return false;
+  }
+  const actual = Buffer.from(secretHeader, "utf-8");
+  const expected = Buffer.from(expectedSecret, "utf-8");
+  return actual.length === expected.length && timingSafeEqual(actual, expected);
+}
+
 export async function startTelegramWebhook(opts: {
   token: string;
   accountId?: string;
@@ -147,6 +170,13 @@ export async function startTelegramWebhook(opts: {
     if (diagnosticsEnabled) {
       logWebhookReceived({ channel: "telegram", updateType: "telegram-post" });
     }
+    const secretHeader = resolveSingleHeaderValue(req.headers["x-telegram-bot-api-secret-token"]);
+    if (!hasValidTelegramWebhookSecret(secretHeader, secret)) {
+      res.shouldKeepAlive = false;
+      res.setHeader("Connection", "close");
+      respondText(401, "unauthorized");
+      return;
+    }
     void (async () => {
       const body = await readJsonBodyWithLimit(req, {
         maxBytes: TELEGRAM_WEBHOOK_MAX_BODY_BYTES,
@@ -189,8 +219,6 @@ export async function startTelegramWebhook(opts: {
         replied = true;
         respondText(401, "unauthorized");
       };
-      const secretHeaderRaw = req.headers["x-telegram-bot-api-secret-token"];
-      const secretHeader = Array.isArray(secretHeaderRaw) ? secretHeaderRaw[0] : secretHeaderRaw;
 
       await handler(body.value, reply, secretHeader, unauthorized);
       if (!replied) {