unsafeWindow

Description

This API object allows a User script to access "custom" properties--variable and functions defined in the page--set by the web page. The unsafeWindow object is shorthand for window.wrappedJSObject. It is the raw window object inside the XPCNativeWrapper provided by the Greasemonkey Sandbox.

• USE OF UNSAFEWINDOW IS INSECURE, AND IT SHOULD BE AVOIDED WHENEVER POSSIBLE.

unsafeWindow bypasses the Greasemonkey XPCNativeWrapper-based Security model, which exists to make sure that malicious web pages cannot alter objects in such a way as to make greasemonkey scripts (which execute with more privileges than ordinary JavaScript running in a web page) do things that their authors or users did not intend. User scripts should therefore avoid calling or in any other way depending on any properties on unsafeWindow - especially if they are executed for arbitrary web pages, such as those with @include, where the page authors may have subverted the environment in this way.

User script authors are strongly encouraged to learn how XPCNativeWrappers work, and how to perform the desired function within their security context, instead of using unsafeWindow to break out.

⬆ ⬇ | Examples | Alternatives to unsafeWindow | Notes

Syntax

unsafeWindow

Value: Object
Returns: Variant
Compatibility: Greasemonkey 0.5b+
Access: @grant

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Examples

⬆ ⬇

Core

unsafeWindow.SomeVarInPage = "Testing";

or

unsafeWindow.SomeFunctionInPage("Test");

or

var oldFunction = unsafeWindow.SomeFunctionInPage;
unsafeWindow.SomeFunctionInPage = function(text) {
  alert("Hijacked! Argument was " + text + ".");
  return oldFunction(text);
};

⬆ ⬇ ⇧

Alternatives to unsafeWindow

⬆ ⬇ | Events | Functions defined in the page | Attach script to page

Events

Event listeners never need to be created on unsafeWindow. Rather than using

unsafeWindow.onclick = function(event) { /* some code */ };

use:

window.addEventListener("click", function(event) { /* some code */ }, false);

See also addEventListener at MDN

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Functions defined in the page

If a user script must execute a page function, it can use the Location hack to call it safely. This involves setting location.href to a javascript: URL, which is like using a bookmarklet. For example:

location.href = "javascript:void(pageFunc(123));";

Larger blocks of code independent of the Greasemonkey context/APIs can also be executed this way:

location.href = "javascript:(" + function() {
  /*
    Some code here.
      Note that the Greasemonkey API is not directly accessible within this function.
  */
} + ")();";

or a more specific example:

location.href = "javascript:(" + encodeURI(uneval(function() { /* some code */ })) + ")();";

This code will run in the page context without leaking the Sandbox. This code is completely separate from the rest of the script scope, sometimes limiting its usefulness. For example, data cannot be returned by the function.

Another drawback is that this technique is rather ugly. Still, it is preferred over unsafeWindow.

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Attach script to page

⬆ ⬇ ⇧ | Method 1 | Method 2 | Method 3

Method 1

function myScript() {
  for (var x in document) {
    /* some code with x */
  }
  /* some code */
}

/**
 * Attaches script into page body and executes it via an anonymous function call.
 *
 * NOTES: Script can therefore reference variables on the page, but likewise
 * cannot use Greasemonkey API methods
 *
 */

var script = document.createElement("script");
script.type = "application/javascript";
script.textContent = "(" + myScript + ")();";

document.body.appendChild(script);

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Method 2

window.addEventListener(
  "DOMTitleChanged",
  function() {
    var redirectURL = window.name;
  },
  false
);

var sGetter = document.createElement("script");
sGetter.type = "application/javascript";
sGetter.textContent =
    "function uXHR(url) {"
  + "  var xhr = new XMLHttpRequest();"
  + "  xhr.onreadystatechange = function() { "
  + "    if (xhr.status == 301 || xhr.status == 302) {"
  + "      window.name = xhr.getResponseHeader('Location');"
  + "      document.title = document.title;"
  + "    }"
  + "  };"
  + "  xhr.open('HEAD', url, true);"
  + "  xhr.send(null);"
  + "}";

document.body.appendChild(sGetter);

unsafeWindow.uXHR(url);

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Method 3

Place this code at the very beginning of the script to inject the entire script into the page using the location hack. Like Method 1, this will give the script access to variables on the page, but not access to Greasemonkey API methods.

if (typeof window.wrappedJSObject == "object") {
  location.href = "javascript:(" + encodeURI(arguments.callee.toSource()) + ")();";
  return;
}

Be very careful when using the wrappedJSObject property. It can be just as dangerous as unsafeWindow is.

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Notes

BUG: In Firefox 3.0.x the prototype field will always be undefined for objects accessed through unsafeWindow. Method 1 can be used as a workaround for this problem.

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