I want to retrieve the RTF content from the Clipboard(Orginating from MSWord).
Is it possible to retrieve it using javascript / JQuery methods?
In general, no. You can only get it if the user triggers a paste. WebKit provides a means to access the clipboard during a paste event and IE provides a clipboardData object that sometimes allows this (depending on the security settings) but that's it.
You can use a hack to effectively redirect a user paste into an off-screen element. See my answer here: JavaScript get clipboard data on paste event (Cross browser)
Related
I develop an addon for Firefox and have the next question: is there a way to paste data from clipboard to borwser elements like a search or url field using Firefox addon api? And what is the best way to solve such kind of problem?
Yes get the data on the clipboard with: paste data from clipboard using document.execCommand("paste"); within firefox extension
Then do Services.wm.getMostRecentWindow('navigator:browser').gURLBar.value = varHoldingPasteData;
I am planning to create an open source education web app where people can add and edit the content (a bit like Wikipedia).
However I wish to add another feature that allows the user to add their own interactive content using JavaScript. (similar how JSFiddle does it)
What are the security concerns in doing this?
Optional question: How can these issues be overcome?
Yes you could use HTML5 Sandbox to only load user scripts in an IFrame.
You should only host user content from a different domain than your main site. This will prevent any XSS attack if an attacker convinces a user to visit the page directly (outside of the sandbox). e.g. if your site is www.example.com you could use the following code to display the sandboxed IFrame (note .org rather than .com, which is an entirely different domain):
<iframe src="https://www.example.org/show_user_script.aspx?id=123" sandbox="allow-scripts"></iframe>
This will allow scripts, but forms and navigation outside of the IFrame will be prevented. Note that this approach could still risk a user hosting a phishing form to capture credentials. You should make sure that the boundaries between your site and the user content are clear within the user interface. Even though we haven't specified allow-forms, this only prevents a form from being submitted directly, it does not prevent form elements and JavaScript event handlers from sending any data to an external domain.
The HTML5 Security Cheat Sheet guidance on OWASP states this is the purpose of the sandbox:
Use the sandbox attribute of an iframe for untrusted content
You should test whether sandbox is supported first, before rendering the IFrame:
<iframe src="/blank.htm" sandbox="allow-scripts" id="foo"></iframe>
var sandboxSupported = "sandbox" in document.createElement("iframe");
if (sandboxSupported) {
document.getElementById('foo').setAttribute('src', 'https://www.example.org/show_user_script.aspx?id=123');
}
else
{
// Not safe to display IFrame
}
It is safer to do it this way by dynamically changing the src rather than redirecting away if sandboxSupported is false because then the iframe will not accidentally be rendered if the redirect doesn't happen in time.
As a simpler alternative, without the need to check whether the sandbox is supported, you can use the srcdoc IFrame attribute to generate the sandboxed content, making sure that all content is HTML encoded:
e.g.
<html><head></head><body>This could be unsafe</body></html>
would be rendered as
<iframe srcdoc="<html><head></head><body>This could be unsafe</body></html>" sandbox="allow-scripts"></iframe>
Or you could construct a data blob object, being careful to HTML encode again:
<body data-userdoc="<html><head></head><body>This could be unsafe</body></html>">
<script>
var unsafeDoc = new Blob([document.body.dataset.userdoc], {type: 'text/html'});
var iframe = document.createElement('iframe');
iframe.src = window.URL.createObjectURL(unsafeDoc);
iframe.sandbox = 'allow-scripts';
</script>
Of course you could also set the unsafeDoc variable from a JSON data source. It is not recommended to load an HTML file, as this has the same problem of it having to be from an external domain, as the attacker could just entice the user to load that directly.
Also, please don't be tempted to write user content into a script block directly. As shown above, data attributes is the safe way to do this, as long as correct HTML encoding is carried out on the user data as it is output server-side.
In these cases you can leave src as blank.html as older browsers that do not support srcdoc will simply load that URL.
As #Snowburnt touches upon, there is nothing stopping a user script from redirecting a user to a site where a drive-by download occurs, but this approach, assuming a user is up to date on patches, and there are no zero day vulnerabilities, this is a safe approach because it protects its end users and their data on your site via the same origin policy.
One big issue is cross-site scripting where users add code that tells the browser to open and run code from other sites. Say they add something that creates an iFrame or a hidden iFrame pointing to a site and starts downloading malicious code.
There's no simple way around it (thanks to Bergi in the comments) to make sure no elements are created and no ajax calls are made.
I've been a member of sites that provided this functionality, but for those sites I paid for my own space so any vulnerabilities I add are inconveniencing my own clients, in that case it's a little more okay to let that slip by since it's not a security leak for everyone.
One way around this is to create customizable controls for the users to use to add interactivity. The plus is that you control the javascript being added, the minus is that your user base will have to request and then wait for you to create them.
We know it's possible to look up the IP of a visitor using JSON and a callback, as seen here Can I perform a DNS lookup (hostname to IP address) using client-side Javascript? and also at http://news.ycombinator.com/item?id=1896015 - but what about a similar thing for the user agent?
This string is directly available in navigator.userAgent. However, this string is not very reliable, because the user can easily modify it. Only use it for non-critical purposes.
If you want to detect the user agent, so that you "know" what's supported, you'd better switch to capability-detection.
Examples of alternative methods to detect the browser:
IE: Conditional comments (HTML (also includes IE version) or in JScript)
Firefox / Webkit / Opera: Setting a CSS property with a vendor-prefix, and checking for the existence of the just-set property.
navigator.userAgent contains the user agent string of the browser.
I have a html page on my localhost - get_description.html.
The snippet below is part of the code:
<input type="text" id="url"/>
<button id="get_description_button">Get description</button>
<iframe id="description_container" src="#"/>
When the button is clicked the src of the iframe is set to the url entered in the textbox. The pages fetched this way are very big with lots of linked files. What I am interested in the page is a block of text contained in a <div id="description"> element.
Is there a way to mitigate downloading of resources linked in the page that loads into the iframe?
I don't want to use curl because the data is only available to logged in users and the steps to take with curl to get the content is too complicated. The iframe is simple as I use this on a box which sends the right cookies to identify the request as coming from a logged in user, but the problem is that it is very wasteful to get nearly 1 MB of data to keep 1 KB of it and throw out the rest.
Edit
If the proposed method just works in Firefox it is fine, so I added Firefox tag. Also, it is possible that the answer actually is from the realm of Firefox add-on techniques, so I added that tag as well.
The problem is not that I cannot get at what I'm looking for, rather, the problem is the easy iframe method is wasteful.
I know that Firefox does allow loading only the text of a page. If you open a page and press Ctrl+U you are taken to 'view page source' window, There links behave as normal and are clickable, if you click on a link in source view, the source of the new page is loaded into the view source window, without the linked resources being downloaded, exactly what I'm trying to get. But I don't know how to access this behaviour.
Another example is the Adblock add-on. It somehow kills elements before they get loaded. With plain Javascript this is not possible. Because it only is triggered too late to intervene in good time.
The Same Origin Policy forbids any web page to access contents of any other web page in a different domain so basically you cannot do that.
However it seems that with some browsers it is allowed to access web pages content if you are trying to access it from a local web page which seems to be your case.
Safari, IE 6/7/8 are browser that allow a local web page to do so via XMLHttpRequest (source: Google Browser Security Handbook) so you may want to choose to use one of those browsers to do what you need (note that future versions of those browsers may not allow to do so anymore).
A part from this solution I only see two possibities:
If the web pages you need to fetch content from are somehow controlled by you, you can create a simpler interface to let other web pages to get the content you need (for example allowing JSONP requests).
If the web pages you need to fetch content from are not controlled by you the only solution I see is to fetch content server side logging in from the server directly (I know that you don't want to do so, but I don't see any other possibility if the previous I mentioned are not practicable)
Hope it helps.
Actually I've seen Cross Domain jQuery .load request before, here: http://james.padolsey.com/javascript/cross-domain-requests-with-jquery/
The author claims that codes like these found on that page
$('#container').load('http://google.com'); // SERIOUSLY!
$.ajax({
url: 'http://news.bbc.co.uk',
type: 'GET',
success: function(res) {
var headline = $(res.responseText).find('a.tsh').text();
alert(headline);
}
});
// Works with $.get too!
would work. (The BBC code might not work because of the recent redesign, but you get the idea)
Apparently it is using YQL wrapped into a jQuery plugin to do the trick. Now I cannot say I fully understand what he is doing there but it appears to work, and fits the bill. Once you load the data I suppose it is a simple matter of filtering out the data that you need.
If you prefer something that works at the browser level, may I suggest Mozilla's Jetpack framework for lightweight extensions. I've not yet read the documentations in its entirety but it should contain the APIs needed for this to work.
There are various ways to go about this in AJAX, I'm going to show the jQuery way for brevity as one option, though you could do this in vanilla JavaScript as well.
Instead of an <iframe> you can just use a container, let's say a <div> like this:
<div id="description_container"></div>
Then to load it:
$(function() {
$("#get_description_button").click(function() {
$("#description_container").load($("input").val() + " #description");
});
});
This uses the .load() method which takes a string in this format: .load("url selector"), then takes that element in the page and places it's content inside the container you're loading, in this case #description_container.
This is just the jQuery route, mainly to illustrate that yes, you can do what you want, but you don't have to do it exactly like this, just showing the concept is getting what you want from an AJAX request, rather than in an <iframe>.
Your description sounds like you are fetching pages from the same domain (you said that you need to be logged in and have session credentials) so have you tried to use async request via XMLHttpRequest? It might complain if the html on a page is particularly messed up but you chould still be able to get raw text via .responseText and extract what you need with a regex.
How to call a Javascript function declared in my extension, using a html button from my web page?
I have a html page, with a button inside. When the user click the button, it will call a function that I already declared inside my own firefox extension.
Since you control the web page, the easiest and the safest method to do what you want would be to dispatch a custom DOM event in the web page and listen to it in the extension code:
https://developer.mozilla.org/En/Code_snippets/Interaction_between_privileged_and_non-privileged_pages
Here's an example extension I wrote that does exactly this http://mozilla.doslash.org/cw/ (not updated to the most recent Firefox version, but it's clean and should be easy to update).
Your Firefox extension runs in a different Javascript context to your HTML page, so the extension cannot be directly called from the Javascript in your HTML page.
However, you can design the extension to allow access from HTML. HTML Javascript isn't generally allowed to access the Component object, so you need to allow the HTML code a way to get at the object in your extension. To do this, create an XPCOM component in your extension, and set the object in the "JavaScript global property" category through the nsICategoryManager object. The entry name is the string used from unprivileged Javascript, the value is the contract ID for your XPCOM class.
However, you also need to allow unprivileged Javascript access to your object, or the script security manager will block access. To allow this, implement nsISecurityCheckedComponent - providing canCreateWrapper(in nsIIDPtr iid), canCallMethod(in nsIIDPtr iid, in wstring methodName), canGetProperty(in nsIIDPtr iid, in wstring propertyName) and canSetProperty(in nsIIDPtr iid, in wstring propertyName) to return allAccess for the allowed properties, and noAccess otherwise.
Be careful what you do with user input, and what you allow access to - it is very easy to accidentally create a security hole in the browser doing this.
Try to put this at the beginning of your javascript function that tries to access a local file:
netscape.security.PrivilegeManager.enablePrivilege('UniversalXPConnect');
This will give the user the choice as to whether they want to allow your code to access the local filesystem.