diff --git a/extensions/google/transport-stream.test.ts b/extensions/google/transport-stream.test.ts
index d295c29f9a72..eb388b55a49e 100644
--- a/extensions/google/transport-stream.test.ts
+++ b/extensions/google/transport-stream.test.ts
@@ -1108,6 +1108,55 @@ describe("google transport stream", () => {
     expect(result.content).toEqual([{ type: "text", text: "ok" }]);
   });
 
+  it("rejects oversized authorized_user ADC token responses", async () => {
+    const tempDir = await mkdtemp(path.join(os.tmpdir(), "openclaw-google-vertex-adc-large-"));
+    const credentialsPath = path.join(tempDir, "application_default_credentials.json");
+    await writeFile(
+      credentialsPath,
+      JSON.stringify({
+        type: "authorized_user",
+        client_id: "client-id",
+        client_secret: "client-secret",
+        refresh_token: "large-refresh-token",
+      }),
+      "utf8",
+    );
+    vi.stubEnv("GOOGLE_APPLICATION_CREDENTIALS", credentialsPath);
+    const tokenFetchMock = vi
+      .fn()
+      .mockResolvedValue(new Response("x".repeat(1024 * 1024 + 1), { status: 200 }));
+
+    await expect(resolveGoogleVertexAuthorizedUserHeaders(tokenFetchMock)).rejects.toThrow(
+      "Google OAuth token response exceeds 1048576 bytes",
+    );
+  });
+
+  it("rejects authorized_user ADC gzip responses that expand past the limit", async () => {
+    const tempDir = await mkdtemp(path.join(os.tmpdir(), "openclaw-google-vertex-adc-bomb-"));
+    const credentialsPath = path.join(tempDir, "application_default_credentials.json");
+    await writeFile(
+      credentialsPath,
+      JSON.stringify({
+        type: "authorized_user",
+        client_id: "client-id",
+        client_secret: "client-secret",
+        refresh_token: "bomb-refresh-token",
+      }),
+      "utf8",
+    );
+    vi.stubEnv("GOOGLE_APPLICATION_CREDENTIALS", credentialsPath);
+    const tokenFetchMock = vi.fn().mockResolvedValue(
+      new Response(gzipSync("x".repeat(1024 * 1024 + 1)), {
+        status: 200,
+        headers: { "content-encoding": "gzip" },
+      }),
+    );
+
+    await expect(resolveGoogleVertexAuthorizedUserHeaders(tokenFetchMock)).rejects.toThrow(
+      "Google OAuth token response exceeds 1048576 decompressed bytes",
+    );
+  });
+
   it("refreshes authorized_user ADC from a compressed token response", async () => {
     const tempDir = await mkdtemp(path.join(os.tmpdir(), "openclaw-google-vertex-adc-gzip-"));
     const credentialsPath = path.join(tempDir, "application_default_credentials.json");
diff --git a/extensions/google/vertex-adc.ts b/extensions/google/vertex-adc.ts
index 9bf2e45c7998..2300fa5de53c 100644
--- a/extensions/google/vertex-adc.ts
+++ b/extensions/google/vertex-adc.ts
@@ -9,6 +9,7 @@ import {
   resolveExpiresAtMsFromDurationMs,
   resolveExpiresAtMsFromDurationSeconds,
 } from "openclaw/plugin-sdk/number-runtime";
+import { readResponseWithLimit } from "openclaw/plugin-sdk/response-limit-runtime";
 import { normalizeOptionalString } from "openclaw/plugin-sdk/string-coerce-runtime";
 
 type GoogleAuthorizedUserCredentials = {
@@ -46,6 +47,7 @@ const GOOGLE_VERTEX_OAUTH_SCOPE = "https://www.googleapis.com/auth/cloud-platfor
 const GOOGLE_VERTEX_TOKEN_EXPIRY_BUFFER_MS = 60_000;
 const GOOGLE_VERTEX_DEFAULT_TOKEN_LIFETIME_SECONDS = 3600;
 const GOOGLE_VERTEX_AUTHLIB_TOKEN_CACHE_MS = 5 * 60_000;
+const GOOGLE_OAUTH_TOKEN_RESPONSE_MAX_BYTES = 1024 * 1024;
 
 let cachedGoogleVertexAuthorizedUserToken: GoogleVertexAuthorizedUserToken | undefined;
 let cachedGoogleAuthClient:
@@ -277,7 +279,10 @@ async function refreshGoogleVertexAuthorizedUserAccessToken(params: {
 async function readGoogleOauthTokenResponsePayload(
   response: Response,
 ): Promise<GoogleOauthTokenResponsePayload | undefined> {
-  const bytes = Buffer.from(await response.arrayBuffer());
+  const bytes = await readResponseWithLimit(response, GOOGLE_OAUTH_TOKEN_RESPONSE_MAX_BYTES, {
+    onOverflow: ({ maxBytes }) =>
+      new Error(`Google OAuth token response exceeds ${maxBytes} bytes`),
+  });
   const text = decodeGoogleOauthTokenResponseBody(bytes, response.headers.get("content-encoding"));
   if (!text.trim()) {
     return undefined;
@@ -292,8 +297,21 @@ async function readGoogleOauthTokenResponsePayload(
 function decodeGoogleOauthTokenResponseBody(bytes: Buffer, contentEncoding: string | null): string {
   if (shouldGunzipGoogleOauthTokenResponse(bytes, contentEncoding)) {
     try {
-      return gunzipSync(bytes).toString("utf8");
-    } catch {
+      return gunzipSync(bytes, { maxOutputLength: GOOGLE_OAUTH_TOKEN_RESPONSE_MAX_BYTES }).toString(
+        "utf8",
+      );
+    } catch (error) {
+      if (
+        typeof error === "object" &&
+        error !== null &&
+        "code" in error &&
+        error.code === "ERR_BUFFER_TOO_LARGE"
+      ) {
+        throw new Error(
+          `Google OAuth token response exceeds ${GOOGLE_OAUTH_TOKEN_RESPONSE_MAX_BYTES} decompressed bytes`,
+          { cause: error },
+        );
+      }
       return bytes.toString("utf8");
     }
   }