Fix JSON injection vulnerability in custom payload handling

- Replaced manual string escaping with `JSON.stringify` to correctly handle all special characters.
- Handled quoting logic for placeholders inside and outside quotes.
- Escaped `$` characters in replacement values to prevent regex replacement issues.
- Added regression tests in `tests/security.test.js`.

Co-authored-by: cmuench <211294+cmuench@users.noreply.github.com>

Author: google-labs-jules[bot]

tests/security.test.js

@@ -0,0 +1,97 @@
+const { sendWebhook } = require('../utils/utils');
+
+// Mock browser API
+const mockBrowser = {
+  tabs: {
+    query: jest.fn()
+  },
+  runtime: {
+    getBrowserInfo: jest.fn(),
+    getPlatformInfo: jest.fn()
+  },
+  i18n: {
+    getMessage: jest.fn((key) => key)
+  }
+};
+
+global.browser = mockBrowser;
+global.fetch = jest.fn();
+global.console.error = jest.fn();
+
+describe('sendWebhook Vulnerability and bugs', () => {
+  beforeEach(() => {
+    jest.clearAllMocks();
+    mockBrowser.tabs.query.mockResolvedValue([{
+      title: 'Test Page',
+      url: 'http://example.com',
+      id: 1,
+      windowId: 1,
+      index: 0,
+      pinned: false,
+      audible: false,
+      incognito: false,
+      status: 'complete'
+    }]);
+    mockBrowser.runtime.getBrowserInfo.mockResolvedValue({ name: 'Firefox' });
+    mockBrowser.runtime.getPlatformInfo.mockResolvedValue({ os: 'linux' });
+    global.fetch.mockResolvedValue({ ok: true });
+  });
+
+  test('should correctly handle backslash in payload (fix JSON syntax error)', async () => {
+    const webhook = {
+      url: 'http://localhost/hook',
+      customPayload: '{ "title": "{{tab.title}}" }',
+      method: 'POST'
+    };
+
+    mockBrowser.tabs.query.mockResolvedValue([{
+      title: '\\',
+      url: 'http://example.com'
+    }]);
+
+    await sendWebhook(webhook, false);
+
+    const callArgs = global.fetch.mock.calls[0];
+    const body = JSON.parse(callArgs[1].body);
+    expect(body.title).toBe('\\');
+  });
+
+  test('should correctly handle escaped quote in payload', async () => {
+    const webhook = {
+      url: 'http://localhost/hook',
+      customPayload: '{ "title": "{{tab.title}}" }',
+      method: 'POST'
+    };
+
+    mockBrowser.tabs.query.mockResolvedValue([{
+      title: '\\"',
+      url: 'http://example.com'
+    }]);
+
+    await sendWebhook(webhook, false);
+
+    const callArgs = global.fetch.mock.calls[0];
+    const body = JSON.parse(callArgs[1].body);
+    expect(body.title).toBe('\\"');
+  });
+
+  test('should correctly handle dollar signs in payload', async () => {
+    const webhook = {
+      url: 'http://localhost/hook',
+      customPayload: '{ "title": "{{tab.title}}" }',
+      method: 'POST'
+    };
+
+    // '$&' is a special replacement pattern (inserts matched string)
+    mockBrowser.tabs.query.mockResolvedValue([{
+      title: '$&',
+      url: 'http://example.com'
+    }]);
+
+    await sendWebhook(webhook, false);
+
+    const callArgs = global.fetch.mock.calls[0];
+    const body = JSON.parse(callArgs[1].body);
+    expect(body.title).toBe('$&');
+  });
+});

utils/utils.js

@@ -158,9 +158,19 @@ async function sendWebhook(webhook, isTest = false) {
           Object.entries(replacements).forEach(([placeholder, value]) => {
             const isPlaceholderInQuotes = customPayloadStr.match(new RegExp(`"[^"]*${placeholder.replace(/[.*+?^${}()|[\]\\]/g, '\\$&')}[^"]*"`));
 
-            const replaceValue = typeof value === 'string'
-              ? (isPlaceholderInQuotes ? value.replace(/"/g, '\\"') : `"${value.replace(/"/g, '\\"')}"`)
-              : (value === undefined ? 'null' : JSON.stringify(value));
+            let replaceValue;
+            if (typeof value === 'string') {
+              replaceValue = JSON.stringify(value);
+              if (isPlaceholderInQuotes) {
+                // Remove the surrounding quotes added by JSON.stringify
+                replaceValue = replaceValue.slice(1, -1);
+              }
+            } else {
+              replaceValue = value === undefined ? 'null' : JSON.stringify(value);
+            }
+
+            // Escape special replacement patterns ($) to prevent them from being interpreted by String.prototype.replace
+            replaceValue = replaceValue.replace(/\$/g, '$$$$');
 
             customPayloadStr = customPayloadStr.replace(
               new RegExp(placeholder.replace(/[.*+?^${}()|[\]\\]/g, '\\$&'), 'g'),