diff --git a/CHANGELOG.md b/CHANGELOG.md
index 03044375933..30ee7687e34 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -102,6 +102,7 @@ Docs: https://docs.openclaw.ai
 - Synology Chat/security: default low-level HTTPS helper TLS verification to on so helper/API defaults match the shipped safe account default, and only explicit `allowInsecureSsl: true` opts out.
 - Android/canvas security: require exact normalized A2UI URL matches before forwarding canvas bridge actions, rejecting query mismatches and descendant paths while still allowing fragment-only A2UI navigation.
 - Cron: send failure notifications through the job's primary delivery channel using the same session context as successful delivery when no explicit `failureDestination` is configured. (#60622) Thanks @artwalker.
+- Gateway/auth: serialize async shared-secret auth attempts per client so concurrent Tailscale-capable failures cannot overrun the intended auth rate-limit budget. Thanks @Telecaster2147.
 
 ## 2026.4.2
 
diff --git a/src/gateway/auth.test.ts b/src/gateway/auth.test.ts
index 9a56dd1a8ed..22a7b6ee161 100644
--- a/src/gateway/auth.test.ts
+++ b/src/gateway/auth.test.ts
@@ -1,5 +1,5 @@
 import { describe, expect, it, vi } from "vitest";
-import type { AuthRateLimiter } from "./auth-rate-limit.js";
+import { createAuthRateLimiter, type AuthRateLimiter } from "./auth-rate-limit.js";
 import {
   assertGatewayAuthConfigured,
   authorizeGatewayConnect,
@@ -349,6 +349,50 @@ describe("gateway auth", () => {
     expect(res.user).toBe("peter");
   });
 
+  it("serializes async auth attempts per rate-limit key", async () => {
+    const limiter = createAuthRateLimiter({
+      maxAttempts: 1,
+      windowMs: 60_000,
+      lockoutMs: 60_000,
+      exemptLoopback: false,
+    });
+    let releaseWhois!: () => void;
+    const whoisGate = new Promise<void>((resolve) => {
+      releaseWhois = resolve;
+    });
+    let whoisCalls = 0;
+    const tailscaleWhois = async () => {
+      whoisCalls += 1;
+      await whoisGate;
+      return null;
+    };
+
+    const baseParams = {
+      auth: { mode: "token" as const, token: "secret", allowTailscale: true },
+      connectAuth: { token: "wrong" },
+      tailscaleWhois,
+      authSurface: "ws-control-ui" as const,
+      req: createTailscaleForwardedReq(),
+      trustedProxies: ["127.0.0.1"],
+      rateLimiter: limiter,
+    };
+
+    const first = authorizeGatewayConnect(baseParams);
+    const second = authorizeGatewayConnect(baseParams);
+
+    await vi.waitFor(() => {
+      expect(whoisCalls).toBe(1);
+    });
+    releaseWhois();
+
+    const [firstResult, secondResult] = await Promise.all([first, second]);
+    expect(firstResult.ok).toBe(false);
+    expect(firstResult.reason).toBe("token_mismatch");
+    expect(secondResult.ok).toBe(false);
+    expect(secondResult.reason).toBe("rate_limited");
+    expect(whoisCalls).toBe(1);
+  });
+
   it("keeps tailscale header auth disabled on HTTP auth wrapper", async () => {
     await expectTailscaleHeaderAuthResult({
       authorize: authorizeHttpGatewayConnect,
diff --git a/src/gateway/auth.ts b/src/gateway/auth.ts
index e445181d9be..b65c51ea3d8 100644
--- a/src/gateway/auth.ts
+++ b/src/gateway/auth.ts
@@ -20,6 +20,7 @@ import {
   resolveClientIp,
 } from "./net.js";
 import { checkBrowserOrigin } from "./origin-check.js";
+import { withSerializedRateLimitAttempt } from "./rate-limit-attempt-serialization.js";
 
 export type ResolvedGatewayAuthMode = "none" | "token" | "password" | "trusted-proxy";
 export type ResolvedGatewayAuthModeSource =
@@ -459,6 +460,41 @@ function authorizeTokenAuth(params: {
 
 export async function authorizeGatewayConnect(
   params: AuthorizeGatewayConnectParams,
+): Promise<GatewayAuthResult> {
+  const { auth, req, trustedProxies } = params;
+  const authSurface = params.authSurface ?? "http";
+  const limiter = params.rateLimiter;
+  const ip =
+    params.clientIp ??
+    resolveRequestClientIp(req, trustedProxies, params.allowRealIpFallback === true) ??
+    req?.socket?.remoteAddress;
+  const rateLimitScope = params.rateLimitScope ?? AUTH_RATE_LIMIT_SCOPE_SHARED_SECRET;
+  const localDirect = isLocalDirectRequest(
+    req,
+    trustedProxies,
+    params.allowRealIpFallback === true,
+  );
+
+  // Keep the limiter strict on the async Tailscale branch by serializing
+  // attempts for the same {scope, ip} key across the pre-check and failure write.
+  if (
+    limiter &&
+    shouldAllowTailscaleHeaderAuth(authSurface) &&
+    auth.allowTailscale &&
+    !localDirect
+  ) {
+    return await withSerializedRateLimitAttempt({
+      ip,
+      scope: rateLimitScope,
+      run: async () => await authorizeGatewayConnectCore(params),
+    });
+  }
+
+  return await authorizeGatewayConnectCore(params);
+}
+
+async function authorizeGatewayConnectCore(
+  params: AuthorizeGatewayConnectParams,
 ): Promise<GatewayAuthResult> {
   const { auth, connectAuth, req, trustedProxies } = params;
   const tailscaleWhois = params.tailscaleWhois ?? readTailscaleWhoisIdentity;
diff --git a/src/gateway/rate-limit-attempt-serialization.ts b/src/gateway/rate-limit-attempt-serialization.ts
new file mode 100644
index 00000000000..7cf79f3e63f
--- /dev/null
+++ b/src/gateway/rate-limit-attempt-serialization.ts
@@ -0,0 +1,36 @@
+import { AUTH_RATE_LIMIT_SCOPE_DEFAULT, normalizeRateLimitClientIp } from "./auth-rate-limit.js";
+
+const pendingAttempts = new Map<string, Promise<void>>();
+
+function normalizeScope(scope: string | undefined): string {
+  return (scope ?? AUTH_RATE_LIMIT_SCOPE_DEFAULT).trim() || AUTH_RATE_LIMIT_SCOPE_DEFAULT;
+}
+
+function buildSerializationKey(ip: string | undefined, scope: string | undefined): string {
+  return `${normalizeScope(scope)}:${normalizeRateLimitClientIp(ip)}`;
+}
+
+export async function withSerializedRateLimitAttempt<T>(params: {
+  ip: string | undefined;
+  scope: string | undefined;
+  run: () => Promise<T>;
+}): Promise<T> {
+  const key = buildSerializationKey(params.ip, params.scope);
+  const previous = pendingAttempts.get(key) ?? Promise.resolve();
+  let releaseCurrent!: () => void;
+  const current = new Promise<void>((resolve) => {
+    releaseCurrent = resolve;
+  });
+  const tail = previous.catch(() => {}).then(() => current);
+  pendingAttempts.set(key, tail);
+
+  await previous.catch(() => {});
+  try {
+    return await params.run();
+  } finally {
+    releaseCurrent();
+    if (pendingAttempts.get(key) === tail) {
+      pendingAttempts.delete(key);
+    }
+  }
+}