I have a web app in Node.js/MySQL where users can upload their stories. They write in an HTML textarea tag. Now I'm trying to get the uploaded from the database using ejs into a script tag so I can do further 'processes'
<script>
var text = "<%=story.Content%>",
result = anchorme.js(text);
document.getElementById('story-content').innerHTML = twemoji.parse(result);
</script>
Problem is if the user hit enter to start on a new line while writing. It'll give me an error here in the text variable and nothing will be printed so how do I fix this?
If you view source on the page so that you can see how the browser receives it, you'll see something like this - note the line feeds:
var text = "I am a story over multiple lines
and that's what javascript gets confused about
because it can't figure out where the closing quotes are.
Let's not even go into what could happen when someone uses quotes!"
So you really just need a way to pass the story content to javascript without it breaking the page. Instead of just pushing out the string like this...
var text = "<%=story.Content%>"
...you can pass stuff to javascript in JSON format as that allows and escapes newlines into \r\n and quotes into \" and so-on. Note the use of <%- rather than <%= here because you don't want it to pass escaped HTML:
var text = <%-JSON.stringify({ content: story.Content })%>.content;
That passes an object with a nicely escaped string in it to your inline script for it to carry on processing.
Related
I've been following this tutorial: http://mariechatfield.com/tutorials/firebase/step5.html
But I wanted to spice it up and instead of printing the last database object, I want to print all of them.
I've tried printing off the database, which works fine. I just need to edit the Html. I tried using a line break, but nothing either. It keeps appending to the starting string instead of making a new line/container.
recommendations.limitToLast(10).on('child_added', function(childSnapshot) {
// Get the recommendation data from the most recent snapshot of data
// added to the recommendations list in Firebase
recommendation = childSnapshot.val();
console.log(recommendation);
// Update the HTML to display the recommendation text
$("#title").append(recommendation.title)
$("#presenter").append(recommendation.presenter)
$("#link").append(recommendation.link)
var x = '\n';
x;
// Make the link actually work and direct to the URL provided
$("#link").attr("href", recommendation.link)
});
I hope to be able to have an individual container for each database element.
Per request, posting comment as answer:
Great job! The only change you have to make is to change \n to <br>. HTML removes whitespace (like your newline). So to replicate that line break you have to use the HTML BR element. Then you'll need to append that to your existing HTML of-course.
I've see a web page that when I try to view the source, I only see a single JavaScript statement. I searched and could not figure out how they have done that. you can do and see yourself.
The web page is: Weird Page
when I view the source I only see something like below which also looks like a comment:
<script type='text/javascript' language='Javascript'>
<!--document.write(unescape('%3C%2........................
................
How they have done that? How I can change my web page so when someone view the source it look like that?
This article may help to clarify what's happening there.
Basically, this company has encoded their entire page using standard escape characters. If you copy the bit from unencode(...) all the way to the next to last parens, and paste it into your browser console, you'll see the actual HTML content.
If you look at the source code for the page I linked, you'll see the function that converts normal text to all escape characters:
// CONVERTS *ALL* CHARACTERS INTO ESCAPED VERSIONS.
function escapeTxt(os){
var ns='';
var t;
var chr='';
var cc='';
var tn='';
for(i=0;i<256;i++){
tn=i.toString(16);
if(tn.length<2)tn="0"+tn;
cc+=tn;
chr+=unescape('%'+tn);
}
cc=cc.toUpperCase();
os.replace(String.fromCharCode(13)+'',"%13");
for(q=0;q<os.length;q++){
t=os.substr(q,1);
for(i=0;i<chr.length;i++){
if(t==chr.substr(i,1)){
t=t.replace(chr.substr(i,1),"%"+cc.substr(i*2,2));
i=chr.length;
}
}
ns+=t;
}
return ns;
}
What is happening is pretty much what it sounds like. The server is serving a single <script> element, which contains an HTML comment to make it easier for browser that don't support JS (read more here: Why does Javascript ignore single line HTML Comments?), and in the comment it's writing to the document the unescaped version of the string, which is sent escaped.
When I allow users to insert data as an argument to the JS innerHTML function like this:
element.innerHTML = “User provided variable”;
I understood that in order to prevent XSS, I have to HTML encode, and then JS encode the user input because the user could insert something like this:
<img src=a onerror='alert();'>
Only HTML or only JS encoding would not help because the .innerHTML method as I understood decodes the input before inserting it into the page. With HTML+JS encoding, I noticed that the .innerHTML decodes only the JS, but the HTML encoding remains.
But I was able to achieve the same by double encoding into HTML.
My question is: Could somebody provide an example of why I should HTML encode and then JS encode, and not double encode in HTML when using the .innerHTML method?
Could somebody provide an example of why I should HTML encode and then
JS encode, and not double encode in HTML when using the .innerHTML
method?
Sure.
Assuming the "user provided data" is populated in your JavaScript by the server, then you will have to JS encode to get it there.
This following is pseudocode on the server-side end, but in JavaScript on the front end:
var userProdividedData = "<%=serverVariableSetByUser %>";
element.innerHTML = userProdividedData;
Like ASP.NET <%= %> outputs the server side variable without encoding. If the user is "good" and supplies the value foo then this results in the following JavaScript being rendered:
var userProdividedData = "foo";
element.innerHTML = userProdividedData;
So far no problems.
Now say a malicious user supplies the value "; alert("xss attack!");//. This would be rendered as:
var userProdividedData = ""; alert("xss attack!");//";
element.innerHTML = userProdividedData;
which would result in an XSS exploit where the code is actually executed in the first line of the above.
To prevent this, as you say you JS encode. The OWASP XSS prevention cheat sheet rule #3 says:
Except for alphanumeric characters, escape all characters less than
256 with the \xHH format to prevent switching out of the data value
into the script context or into another attribute.
So to secure against this your code would be
var userProdividedData = "<%=JsEncode(serverVariableSetByUser) %>";
element.innerHTML = userProdividedData;
where JsEncode encodes as per the OWASP recommendation.
This would prevent the above attack as it would now render as follows:
var userProdividedData = "\x22\x3b\x20alert\x28\x22xss\x20attack\x21\x22\x29\x3b\x2f\x2f";
element.innerHTML = userProdividedData;
Now you have secured your JavaScript variable assignment against XSS.
However, what if a malicious user supplied <img src="xx" onerror="alert('xss attack')" /> as the value? This would be fine for the variable assignment part as it would simply get converted into the hex entity equivalent like above.
However the line
element.innerHTML = userProdividedData;
would cause alert('xss attack') to be executed when the browser renders the inner HTML. This would be like a DOM Based XSS attack as it is using rendered JavaScript rather than HTML, however, as it passes though the server it is still classed as reflected or stored XSS depending on where the value is initially set.
This is why you would need to HTML encode too. This can be done via a function such as:
function escapeHTML (unsafe_str) {
return unsafe_str
.replace(/&/g, '&')
.replace(/</g, '<')
.replace(/>/g, '>')
.replace(/\"/g, '"')
.replace(/\'/g, ''')
.replace(/\//g, '/')
}
making your code
element.innerHTML = escapeHTML(userProdividedData);
or could be done via JQuery's text() function.
Update regarding question in comments
I just have one more question: You mentioned that we must JS encode
because an attacker could enter "; alert("xss attack!");//. But if we
would use HTML encoding instead of JS encoding, wouldn't that also
HTML encode the " sign and make this attack impossible because we
would have: var userProdividedData =""; alert("xss attack!");//";
I'm taking your question to mean the following: Rather than JS encoding followed by HTML encoding, why don't we don't just HTML encode in the first place, and leave it at that?
Well because they could encode an attack such as <img src="xx" onerror="alert('xss attack')" /> all encoded using the \xHH format to insert their payload - this would achieve the desired HTML sequence of the attack without using any of the characters that HTML encoding would affect.
There are some other attacks too: If the attacker entered \ then they could force the browser to miss the closing quote (as \ is the escape character in JavaScript).
This would render as:
var userProdividedData = "\";
which would trigger a JavaScript error because it is not a properly terminated statement. This could cause a Denial of Service to the application if it is rendered in a prominent place.
Additionally say there were two pieces of user controlled data:
var userProdividedData = "<%=serverVariableSetByUser1 %>" + ' - ' + "<%=serverVariableSetByUser2 %>";
the user could then enter \ in the first and ;alert('xss');// in the second. This would change the string concatenation into one big assignment, followed by an XSS attack:
var userProdividedData = "\" + ' - ' + ";alert('xss');//";
Because of edge cases like these it is recommended to follow the OWASP guidelines as they are as close to bulletproof as you can get. You might think that adding \ to the list of HTML encoded values solves this, however there are other reasons to use JS followed by HTML when rendering content in this manner because this method also works for data in attribute values:
<a href="javascript:void(0)" onclick="myFunction('<%=JsEncode(serverVariableSetByUser) %>'); return false">
Despite whether it is single or double quoted:
<a href='javascript:void(0)' onclick='myFunction("<%=JsEncode(serverVariableSetByUser) %>"); return false'>
Or even unquoted:
<a href=javascript:void(0) onclick=myFunction("<%=JsEncode(serverVariableSetByUser) %>");return false;>
If you HTML encoded like mentioned in your comment an entity value:
onclick='var userProdividedData ="";"' (shortened version)
the code is actually run via the browser's HTML parser first, so userProdividedData would be
";;
instead of
";
so when you add it to the innerHTML call you would have XSS again. Note that <script> blocks are not processed via the browser's HTML parser, except for the closing </script> tag, but that's another story.
It is always wise to encode as late as possible such as shown above. Then if you need to output the value in anything other than a JavaScript context (e.g. an actual alert box does not render HTML, then it will still display correctly).
That is, with the above I can call
alert(serverVariableSetByUser);
just as easily as setting HTML
element.innerHTML = escapeHTML(userProdividedData);
In both cases it will be displayed correctly without certain characters from disrupting output or causing undesirable code execution.
A simple way to make sure the contents of your element is properly encoded (and will not be parsed as HTML) is to use textContent instead of innerHTML:
element.textContent = "User provided variable with <img src=a>";
Another option is to use innerHTML only after you have encoded (preferably on the server if you get the chance) the values you intend to use.
I have faced this issue in my ASP.NET Webforms application. The fix to this is relatively simple.
Install HtmlSanitizationLibrary from NuGet Package Manager and refer this in your application. At the code behind, please use the sanitizer class in the following way.
For example, if the current code looks something like this,
YourHtmlElement.InnerHtml = "Your HTML content" ;
Then, replace this with the following:
string unsafeHtml = "Your HTML content";
YourHtmlElement.InnerHtml = Sanitizer.GetSafeHtml(unsafeHtml);
This fix will remove the Veracode vulnerability and make sure that the string gets rendered as HTML. Encoding the string at code behind will render it as 'un-encoded string' rather than RAW HTML as it is encoded before the render begins.
Perhaps this is expected, but I found it odd since I am now starting with jQuery.
So, I am writing an application using node and jade. In the index.jade I have a statement of the form
p Welcome subscriber
span(id="subscriber") someID
Now once the connection is established between the client and the server, the server sends a welcome JSON message with some data. One of them is the id of the client which I want to replace above. Once the client receives the welcome JSON message it initializes the appropriate structures and then I make a call to a function loadStats:
function loadStats() {
var myText = "" + myData.id + ".";
$('#subscriber').text(myText);
$('#subscriber').html(myText);
};
In the screen I can see that the text "someID" is replaced by the ID of the client. However, when I actually inspect the html code of the page that I am looking at I see a statement of the form:
<p>Welcome subscriber <span id="subscriber">someID</span></p>
In other words in the actual HTML code the text "someID" has not been replaced. Is this something expected? How was the replacement done? Moreover, it appears that working with either of the statements
$('#subscriber').text(myText);
$('#subscriber').html(myText);
gives the replication on the screen but not on the actual html content of what is presented on screen. Is this the correct behavior? From what I understood (and expect) the .text() replaces the visual data of the element with the specific id and the .html() replaces the content. Am I missing something?
Thanks in advance. jQuery rookie here.
Two rules for expressions in pug:
In attributes you use quotes to output literal text and you leave the quotes out when you want to use a variable, and
For the content of a tag you use an equals sign when you want pug to evaluate an expression, or don't put anything if you want literal text
So with those rules in mind, looking at your code you will output the attribute "subscriber" as a literal and "someId" as a literal.
span(id="subscriber") someID
Results in:
<span id="subscriber">someId</span>
You wanted both to be dynamic so remove the quotes in the attribute and put an equals sign after the element:
span(id= subscriber)= someID
This will dynamically replace both with variables.
I'm trying to create a function in javascript (or jQuery) that will take a variable filled with html and output a plain text version. The function needs to strip the html tags and insert line breaks at the end of heading and paragraph tags.
I've been going round in circles for ages with this. There are lots of examples of how to take a DOM object, e.g. document.body.innerHTML and remove the tags. However, I'm using a variable filled with html and the results are not the same.
This is the supposed duplicate solution: http://jsfiddle.net/8JSZX/. However, create an html variable and use that and you get: http://jsfiddle.net/JjXXY/ - which does not preserve the line breaks.
The html variable would be something like:
var html = '<h1>This is a heading</h1><p>This is a paragraph</p><p>This is another paragraph</p>'
If there is a better solution to this I'm open to suggestions!
Gave it a shot:
var html_string = '<h1>Test</h1><p>A paragraph with a link</p>';
var regex = /<(\/?)[a-zA-Z0-9][^>]*>/g;
var stripped = html_string.replace(regex, '');
$("#result").html(stripped);
See: http://jsfiddle.net/Y6q2j/5/