fix(nextcloud-talk): replace manual XOR with crypto.timingSafeEqual and fix length leak

extensions/nextcloud-talk/src/core.test.ts

@@ -131,6 +131,99 @@ describe("nextcloud talk core", () => {
     ).toBeNull();
   });
 
+  it("still runs timingSafeEqual when the supplied signature length mismatches", async () => {
+    const timingSafeEqualMock = vi.fn();
+
+    vi.resetModules();
+    vi.doMock("node:crypto", async (importOriginal) => {
+      const actual = await importOriginal<typeof import("node:crypto")>();
+      return {
+        ...actual,
+        timingSafeEqual: vi.fn((left: NodeJS.ArrayBufferView, right: NodeJS.ArrayBufferView) => {
+          timingSafeEqualMock(left, right);
+          return actual.timingSafeEqual(left, right);
+        }),
+      };
+    });
+
+    const { generateNextcloudTalkSignature, verifyNextcloudTalkSignature } =
+      await import("./signature.js");
+    const body = JSON.stringify({ hello: "world" });
+    const generated = generateNextcloudTalkSignature({
+      body,
+      secret: "secret-123",
+    });
+    const shortSignature = generated.signature.slice(0, 12);
+
+    expect(
+      verifyNextcloudTalkSignature({
+        signature: shortSignature,
+        random: generated.random,
+        body,
+        secret: "secret-123",
+      }),
+    ).toBe(false);
+
+    expect(timingSafeEqualMock).toHaveBeenCalledOnce();
+    const [leftBuffer, rightBuffer] = timingSafeEqualMock.mock.calls[0] ?? [];
+    expect(Buffer.isBuffer(leftBuffer)).toBe(true);
+    expect(Buffer.isBuffer(rightBuffer)).toBe(true);
+    if (!Buffer.isBuffer(leftBuffer) || !Buffer.isBuffer(rightBuffer)) {
+      throw new TypeError("Expected timingSafeEqual to receive Buffer arguments");
+    }
+    expect(leftBuffer).toHaveLength(rightBuffer.length);
+
+    vi.doUnmock("node:crypto");
+    vi.resetModules();
+  });
+
+  it("rejects tampered bodies, wrong secrets, and tampered signatures", () => {
+    const body = JSON.stringify({ hello: "world" });
+    const generated = generateNextcloudTalkSignature({
+      body,
+      secret: "secret-123",
+    });
+
+    expect(
+      verifyNextcloudTalkSignature({
+        signature: generated.signature,
+        random: generated.random,
+        body: JSON.stringify({ hello: "tampered" }),
+        secret: "secret-123",
+      }),
+    ).toBe(false);
+    expect(
+      verifyNextcloudTalkSignature({
+        signature: generated.signature,
+        random: generated.random,
+        body,
+        secret: "wrong-secret",
+      }),
+    ).toBe(false);
+    expect(
+      verifyNextcloudTalkSignature({
+        signature: "a".repeat(generated.signature.length),
+        random: generated.random,
+        body,
+        secret: "secret-123",
+      }),
+    ).toBe(false);
+  });
+
+  it("takes the first value from array-backed headers", () => {
+    expect(
+      extractNextcloudTalkHeaders({
+        "x-nextcloud-talk-signature": ["sig1", "sig2"],
+        "x-nextcloud-talk-random": ["rand1", "rand2"],
+        "x-nextcloud-talk-backend": ["backend1", "backend2"],
+      }),
+    ).toEqual({
+      signature: "sig1",
+      random: "rand1",
+      backend: "backend1",
+    });
+  });
+
   it("persists replay decisions across guard instances and scopes account namespaces", async () => {
     const stateDir = await makeTempDir();
 

extensions/nextcloud-talk/src/signature.ts

@@ -1,4 +1,4 @@
-import { createHmac, randomBytes } from "node:crypto";
+import { createHmac, randomBytes, timingSafeEqual } from "node:crypto";
 import { normalizeLowercaseStringOrEmpty } from "openclaw/plugin-sdk/text-runtime";
 import type { NextcloudTalkWebhookHeaders } from "./types.js";
 
@@ -25,14 +25,23 @@ export function verifyNextcloudTalkSignature(params: {
     .update(random + body)
     .digest("hex");
 
-  if (signature.length !== expected.length) {
-    return false;
-  }
-  let result = 0;
-  for (let i = 0; i < signature.length; i++) {
-    result |= signature.charCodeAt(i) ^ expected.charCodeAt(i);
-  }
-  return result === 0;
+  const expectedBuf = Buffer.from(expected, "utf8");
+  const signatureBuf = Buffer.from(signature, "utf8");
+
+  // Pad to equal length before constant-time comparison to prevent
+  // leaking length information via early-return timing.
+  // Note: digest("hex") always produces lowercase ASCII (64 bytes for SHA-256),
+  // so expectedBuf is always 64 bytes — no variable-length concern on the expected side.
+  const maxLen = Math.max(expectedBuf.length, signatureBuf.length);
+  const paddedExpected = Buffer.alloc(maxLen);
+  const paddedSignature = Buffer.alloc(maxLen);
+  expectedBuf.copy(paddedExpected);
+  signatureBuf.copy(paddedSignature);
+
+  // Use crypto.timingSafeEqual instead of manual XOR loop to avoid
+  // potential JIT-optimisation timing leaks in the JavaScript engine.
+  const timingResult = timingSafeEqual(paddedExpected, paddedSignature);
+  return expectedBuf.length === signatureBuf.length && timingResult;
 }
 
 /**