fix(signal): reject malformed base64 attachment data (#114883)

signalRpcRequest returns the JSON-RPC result via a bare cast, so getAttachment data reaches Buffer.from unvalidated. Node drops out-of-alphabet characters instead of throwing, so a damaged payload was silently written to disk as a corrupted attachment. Canonicalize after the existing size guard and fail with the attachment id instead.

extensions/signal/src/monitor.attachment-base64.test.ts

@@ -0,0 +1,93 @@
+import type { OpenClawConfig } from "openclaw/plugin-sdk/config-contracts";
+import { beforeEach, describe, expect, it, vi } from "vitest";
+import type { SignalEventHandlerDeps } from "./monitor/event-handler.types.js";
+
+const signalRpcRequestMock = vi.hoisted(() => vi.fn());
+const saveMediaBufferMock = vi.hoisted(() => vi.fn());
+
+let capturedFetchAttachment: SignalEventHandlerDeps["fetchAttachment"] | undefined;
+
+vi.mock("openclaw/plugin-sdk/media-runtime", async () => {
+  const actual = await vi.importActual<typeof import("openclaw/plugin-sdk/media-runtime")>(
+    "openclaw/plugin-sdk/media-runtime",
+  );
+  return {
+    ...actual,
+    saveMediaBuffer: saveMediaBufferMock,
+  };
+});
+
+vi.mock("./client-adapter.js", async () => {
+  const actual = await vi.importActual<typeof import("./client-adapter.js")>("./client-adapter.js");
+  return {
+    ...actual,
+    signalRpcRequest: signalRpcRequestMock,
+  };
+});
+
+vi.mock("./monitor/event-handler.js", () => ({
+  createSignalEventHandler: (deps: SignalEventHandlerDeps) => {
+    capturedFetchAttachment = deps.fetchAttachment;
+    return async () => {};
+  },
+}));
+
+vi.mock("./signal-ingress.js", () => ({
+  startSignalIngressMonitor: async () => ({
+    receive: async () => {},
+    stop: async () => {},
+  }),
+}));
+
+vi.mock("./sse-reconnect.js", () => ({
+  runSignalSseLoop: async () => {},
+}));
+
+const { monitorSignalProvider } = await import("./monitor.js");
+
+const config = {
+  channels: {
+    signal: {
+      transport: { kind: "external-native", url: "http://127.0.0.1:8080" },
+      dmPolicy: "open",
+      allowFrom: ["*"],
+    },
+  },
+} satisfies OpenClawConfig;
+
+function requireCapturedFetchAttachment(): SignalEventHandlerDeps["fetchAttachment"] {
+  if (!capturedFetchAttachment) {
+    throw new Error("expected monitor to configure fetchAttachment");
+  }
+  return capturedFetchAttachment;
+}
+
+describe("Signal attachment fetch", () => {
+  beforeEach(() => {
+    capturedFetchAttachment = undefined;
+    signalRpcRequestMock.mockReset();
+    saveMediaBufferMock.mockReset().mockResolvedValue({
+      path: "/tmp/signal-attachment.png",
+      contentType: "image/png",
+    });
+  });
+
+  it("rejects malformed base64 attachment data", async () => {
+    signalRpcRequestMock.mockResolvedValue({
+      data: "iVBORw0KGgoAAAANSUhE%%%UgAAAAEAAAABCAYAAAAfFcSJAAAADUlEQVQIW2Nk+M/wHwAF/gL+M6Q10QAAAABJRU5ErkJggg==",
+    });
+
+    await monitorSignalProvider({ config, autoStart: false });
+    const fetchAttachment = requireCapturedFetchAttachment();
+
+    await expect(
+      fetchAttachment({
+        baseUrl: "http://127.0.0.1:8080",
+        attachment: { id: "attachment-123", contentType: "image/png" },
+        sender: "+15550001111",
+        maxBytes: 8 * 1024 * 1024,
+      }),
+    ).rejects.toThrow("Signal attachment attachment-123 returned malformed base64 data");
+    expect(saveMediaBufferMock).not.toHaveBeenCalled();
+  });
+});

extensions/signal/src/monitor.ts

@@ -9,6 +9,7 @@ import type {
   SignalReactionNotificationMode,
 } from "openclaw/plugin-sdk/config-contracts";
 import {
+  canonicalizeBase64,
   detectMime,
   estimateBase64DecodedBytes,
   saveMediaBuffer,
@@ -315,7 +316,11 @@ async function fetchAttachment(params: {
       `Signal attachment ${attachment.id} exceeds ${(params.maxBytes / (1024 * 1024)).toFixed(0)}MB limit`,
     );
   }
-  const buffer = Buffer.from(result.data, "base64");
+  const canonicalData = canonicalizeBase64(result.data);
+  if (!canonicalData) {
+    throw new Error(`Signal attachment ${attachment.id} returned malformed base64 data`);
+  }
+  const buffer = Buffer.from(canonicalData, "base64");
   const originalFilename = normalizeOptionalString(attachment.filename ?? undefined);
   const contentType =
     normalizeOptionalString(attachment.contentType ?? undefined) ??