UnsafeWindow

This command can open certain security holes in your user script, and it is recommended to use this command sparingly.

Please be sure to read the entire article and understand it before using it in a script.

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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 Greasemonkey's 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 - especally if 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+

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Examples

unsafeWindow.SomeVarInPage = "Testing";

unsafeWindow.SomeFunctionInPage("Test");

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

For issues with GM_getValue, GM_setValue and GM_xmlhttpRequest, see see 0.7.20080121.0_compatibility.

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

var sGetter = document.createElement("script");
sGetter.type = "text/javascript";
sGetter.innerHTML = 
  "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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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 MDC

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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:(" + 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

Attach Method 1

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

// attach script to page; script can therefore reference variables on the page, but likewise
// cannot use greasemonkey API methods

document.body.appendChild(document.createElement("script")).innerHTML="(" + myScript + ")()";

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Attach Method 2

This way is interesting for those who want:

• execute the init() function NOT in GM address space
• inject multiple css hacks
• inject multiple .js files (even from different domains)

/* Filename: hello-world.user.js */

(function()
{
  inject_css();
 
  /*
    Define single/multiple script(s) to inject
      NOTES:
        Schemes of file:// type, absolute or implied, are not supported with this method due to
        browser security restrictions.

        Schemes of http:// or https:// must be present, see pitfall 1 and 2 below.
  */

  var scripts = [
    "http://localhost:8080/hello-injecting.js",
    "http://www.example.com/inject-this-script1.js",
    "http://www.example.com/inject-this-script2.js"
  ];

  var script;
  for (i in scripts) {
    script = document.createElement("script");
    script.src = scripts[i];
    script.type = "text/javascript";

    document.getElementsByTagName("head")[0].appendChild(script);
  }
  
  window.addEventListener(
    "load",
    function(event) {
      location.href = "javascript:void(init());";
    },
    false
  );
}
)();

 
 
function inject_css() {
  document.title += ' dynamically modified version';
  GM_addStyle("body { color:white; background-color:black } img { border:0 }");
}

/*
  Filename: http://localhost:8080/hello-injecting.js

  NOTES:
    This means you are running your own web server on port 8080 and hosting this script locally and NOT remotely.
*/

function init() {
  alert('Hello, world!');
}

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Attach Method 2 Pitfall 1

The method of hosting hello-injecting.user.js in Greasemonkey was tested on:

Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9.0.6) Gecko/2009011912 Firefox/3.0.6

Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9.0.7) Gecko/2009021906 Firefox/3.0.7

and failed to execute init() with the following error:

Error: init is not defined

Source file: javascript:void(init());

Line: 1

Possible solution:

Always write the URL your .js file is in with the protocol as:

• correct: http://localhost:8080/hello-injecting.user.js
• incorrect: localhost:8080/hello-injecting.user.js

NOTE: also check that the file is there.

Attach Method 2 Pitfall 2

The method of hosting hello-injecting.js on a local web server as well as a remote web server was tested on:

Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9.0.6) Gecko/2009011912 Firefox/3.0.6

Mozilla/5.0 (X11; U; Linux i686 (x86_64); en-US; rv:1.9.0.7) Gecko/2009021906 Firefox/3.0.7

and returned Component failure code with the following error:

Error: Component returned failure code: 0x805e000a [nsIDOMLocation.href] = <unknown>

Source file: file://~/.mozilla/firefox/randomseed.default/extensions/{class-id}/components/greasemonkey.js

Line: 377

Notes

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