Difference between revisions of "UnsafeWindow"

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m (Minor mention of obvious-to-wizards limitations of the location hack.)
 
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__NOTOC__


== Description ==
== Description ==


This [[API_reference|API]] object allows a [[User script]] to access "custom" properties--variable and functions defined in the page--set by the web page.
This [object allows a [[User script]] to access "custom" properties set by the web page.
 
The user script is otherwise isolated from these properties.
This is done by bypassing [[Greasemonkey]]'s [[XPCNativeWrapper]]-based [[security]] model.
The unsafeWindow object is shorthand for <code>window.wrappedJSObject</code>. 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.'''
:*'''USE OF UNSAFEWINDOW IS INSECURE, AND IT SHOULD BE AVOIDED WHENEVER POSSIBLE.'''
User scripts absolutely should not use unsafeWindow if they are executed for arbitrary web pages, such as those with <code>@[[Include and exclude rules|include]] *</code>.
[[User script]] authors are '''strongly''' encouraged to learn how [[XPCNativeWrapper]]s work, and how to perform the desired function within their security context, instead of using unsafeWindow to break out.
[[#Examples|Examples]] | [[#Alternatives_to_unsafeWindow|Alternatives to unsafeWindow]] | [[#Notes|Notes]]
== Syntax ==
'''unsafeWindow'''
:Value: Object
:Returns: Variant
:Compatibility: [[Version_history#0.5_beta|Greasemonkey 0.5b+]], [[Version_history#0.7.20080121.0|Greasemonkey 0.7.20080121.0+]]


[[#top|top]]
unsafeWindow bypasses [[Greasemonkey]]'s security model, which exists to make sure that malicious web pages cannot alter objects in such a way as to make user 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 <code>@[[Include and exclude rules|include]] *</code>..


== Examples ==
== Examples ==
<code><pre>
unsafeWindow.SomeVarInPage = "Testing";
</pre></code>


<code><pre>
<pre class='sample-bad'>
unsafeWindow.SomeFunctionInPage("Test");
unsafeWindow.SomeVarInPage = "Testing";
</pre></code>
</pre>


<code><pre>
<pre class='sample-bad'>
var oldFunction = unsafeWindow.SomeFunctionInPage;
unsafeWindow.SomeFunctionInPage("Test");
unsafeWindow.SomeFunctionInPage = function(text) {
</pre>
  alert("Hijacked! Argument was " + text + ".");
  return oldFunction(text);
};
</pre></code>


[[#top|top]]
<pre class='sample-bad'>
var oldFunction = unsafeWindow.SomeFunctionInPage;
unsafeWindow.SomeFunctionInPage = function(text) {
  alert('Hijacked! Argument was ' + text + '.');
  return oldFunction(text);
};
</pre>


== Alternatives to unsafeWindow ==
== Alternatives to unsafeWindow ==


[[#Events|Events]] | [[#Functions_defined_in_the_page|Functions defined in the page]]
''Sometimes'', you just can't get around using unsafeWindow.
 
Most of the time, however, you can!
=== Events ===
See [[:Category:Coding Tips:Interacting With The Page]] for details on various methods to interact with the page that do '''not''' use unsafeWindow.
 
:Event listeners never need to be created on unsafeWindow. Rather than using <code>unsafeWindow.onclick = function(event) { ... };</code>, use:
 
:<code><pre>window.addEventListener("click", function(event) { /* some code */ }, false);</pre></code>
 
:*[http://developer.mozilla.org/en/docs/DOM:element.addEventListener addEventListener at MDC]
 
[[#top|top]] | [[#Alternatives_to_unsafeWindow|back]]
 
=== 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 <code>javascript:</code> URL, which is like using a bookmarklet. For example:
 
:<code><pre>location.href = "javascript:void(pageFunc(123));";</pre></code>
 
:Larger blocks of code independent of the Greasemonkey context/APIs can also be executed this way:
 
:<code><pre>location.href = "javascript:(" + encodeURI(uneval(function() { /* some code */ })) + ")();";</pre></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.
 
[[#top|top]] | [[#Alternatives_to_unsafeWindow|back]]
 
== Notes ==
[[#top|top]]


[[Category:API_Reference|U]]  
[[Category:API_Reference|U]]  
[[Category:Scripting context]]
[[Category:Scripting context]]
[[Category:Security]]
[[Category:Security]]

Latest revision as of 15:17, 3 November 2017

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.


Description

This [object allows a User script to access "custom" properties set by the web page. The user script is otherwise isolated from these properties.

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

unsafeWindow bypasses Greasemonkey's security model, which exists to make sure that malicious web pages cannot alter objects in such a way as to make user 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 *..

Examples

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

Alternatives to unsafeWindow

Sometimes, you just can't get around using unsafeWindow. Most of the time, however, you can! See Category:Coding Tips:Interacting With The Page for details on various methods to interact with the page that do not use unsafeWindow.