I don't know what it called, but i think this is possible
I am looking to write something(don't know the exact name) that will,
go to a webpage and select a value from drop-down box on that page and read values from that page after selection, I am not sure weather it called crawler or activity, i am new to this but i heard long time back from one of my friend this can be done,
can any one please give me a head start
Thanks
You need an HTTP client library (perhaps libcurl in C, or some C# wrapper for it, or some native C# HTTP client library like this).
You also need to parse the retrieved HTML content. So you probably need an HTML parsing library (maybe HTML agility pack).
If the targeted webpage is nearly fixed and has e.g. some comments to ease finding the relevant part, you might use simpler or ad-hoc parsing techniques.
Some sites might send a nearly empty static HTML client, with the actual page being dynamically constructed by Javascript scripts (Ajax). In that case, you are unlucky.
Maybe you want some web service ....
One simple way (but not the most efficient way) is to simply read the webpage as String using the WebClient, for example:
WebClient Web = new WebClient();
String Data = Web.DownloadString("Address");
Now since HTML is simply an XML document you can parse the string to a XDocument and look up the tag that represents the dropdown box. Parsing the string to XDocument is done this way:
XDocument xdoc = XDocument.Pase(Data);
Update:
If you want to read the result of the selected value, and that result is displayed within the page do this:
Get all the items as I explained.
If the page does not make use of models, then you can use your selected value as an argument for example :
www.somepage.com/Name=YourItem?
Read the page again and find the value
We have a high security application and we want to allow users to enter URLs that other users will see.
This introduces a high risk of XSS hacks - a user could potentially enter javascript that another user ends up executing. Since we hold sensitive data it's essential that this never happens.
What are the best practices in dealing with this? Is any security whitelist or escape pattern alone good enough?
Any advice on dealing with redirections ("this link goes outside our site" message on a warning page before following the link, for instance)
Is there an argument for not supporting user entered links at all?
Clarification:
Basically our users want to input:
stackoverflow.com
And have it output to another user:
stackoverflow.com
What I really worry about is them using this in a XSS hack. I.e. they input:
alert('hacked!');
So other users get this link:
stackoverflow.com
My example is just to explain the risk - I'm well aware that javascript and URLs are different things, but by letting them input the latter they may be able to execute the former.
You'd be amazed how many sites you can break with this trick - HTML is even worse. If they know to deal with links do they also know to sanitise <iframe>, <img> and clever CSS references?
I'm working in a high security environment - a single XSS hack could result in very high losses for us. I'm happy that I could produce a Regex (or use one of the excellent suggestions so far) that could exclude everything that I could think of, but would that be enough?
If you think URLs can't contain code, think again!
https://owasp.org/www-community/xss-filter-evasion-cheatsheet
Read that, and weep.
Here's how we do it on Stack Overflow:
/// <summary>
/// returns "safe" URL, stripping anything outside normal charsets for URL
/// </summary>
public static string SanitizeUrl(string url)
{
return Regex.Replace(url, #"[^-A-Za-z0-9+&##/%?=~_|!:,.;\(\)]", "");
}
The process of rendering a link "safe" should go through three or four steps:
Unescape/re-encode the string you've been given (RSnake has documented a number of tricks at http://ha.ckers.org/xss.html that use escaping and UTF encodings).
Clean the link up: Regexes are a good start - make sure to truncate the string or throw it away if it contains a " (or whatever you use to close the attributes in your output); If you're doing the links only as references to other information you can also force the protocol at the end of this process - if the portion before the first colon is not 'http' or 'https' then append 'http://' to the start. This allows you to create usable links from incomplete input as a user would type into a browser and gives you a last shot at tripping up whatever mischief someone has tried to sneak in.
Check that the result is a well formed URL (protocol://host.domain[:port][/path][/[file]][?queryField=queryValue][#anchor]).
Possibly check the result against a site blacklist or try to fetch it through some sort of malware checker.
If security is a priority I would hope that the users would forgive a bit of paranoia in this process, even if it does end up throwing away some safe links.
Use a library, such as OWASP-ESAPI API:
PHP - http://code.google.com/p/owasp-esapi-php/
Java - http://code.google.com/p/owasp-esapi-java/
.NET - http://code.google.com/p/owasp-esapi-dotnet/
Python - http://code.google.com/p/owasp-esapi-python/
Read the following:
https://www.golemtechnologies.com/articles/prevent-xss#how-to-prevent-cross-site-scripting
https://www.owasp.org/
http://www.secbytes.com/blog/?p=253
For example:
$url = "http://stackoverflow.com"; // e.g., $_GET["user-homepage"];
$esapi = new ESAPI( "/etc/php5/esapi/ESAPI.xml" ); // Modified copy of ESAPI.xml
$sanitizer = ESAPI::getSanitizer();
$sanitized_url = $sanitizer->getSanitizedURL( "user-homepage", $url );
Another example is to use a built-in function. PHP's filter_var function is an example:
$url = "http://stackoverflow.com"; // e.g., $_GET["user-homepage"];
$sanitized_url = filter_var($url, FILTER_SANITIZE_URL);
Using filter_var allows javascript calls, and filters out schemes that are neither http nor https. Using the OWASP ESAPI Sanitizer is probably the best option.
Still another example is the code from WordPress:
http://core.trac.wordpress.org/browser/tags/3.5.1/wp-includes/formatting.php#L2561
Additionally, since there is no way of knowing where the URL links (i.e., it might be a valid URL, but the contents of the URL could be mischievous), Google has a safe browsing API you can call:
https://developers.google.com/safe-browsing/lookup_guide
Rolling your own regex for sanitation is problematic for several reasons:
Unless you are Jon Skeet, the code will have errors.
Existing APIs have many hours of review and testing behind them.
Existing URL-validation APIs consider internationalization.
Existing APIs will be kept up-to-date with emerging standards.
Other issues to consider:
What schemes do you permit (are file:/// and telnet:// acceptable)?
What restrictions do you want to place on the content of the URL (are malware URLs acceptable)?
Just HTMLEncode the links when you output them. Make sure you don't allow javascript: links. (It's best to have a whitelist of protocols that are accepted, e.g., http, https, and mailto.)
You don't specify the language of your application, I will then presume ASP.NET, and for this you can use the Microsoft Anti-Cross Site Scripting Library
It is very easy to use, all you need is an include and that is it :)
While you're on the topic, why not given a read on Design Guidelines for Secure Web Applications
If any other language.... if there is a library for ASP.NET, has to be available as well for other kind of language (PHP, Python, ROR, etc)
For Pythonistas, try Scrapy's w3lib.
OWASP ESAPI pre-dates Python 2.7 and is archived on the now-defunct Google Code.
How about not displaying them as a link? Just use the text.
Combined with a warning to proceed at your own risk may be enough.
addition - see also Should I sanitize HTML markup for a hosted CMS? for a discussion on sanitizing user input
There is a library for javascript that solves this problem
https://github.com/braintree/sanitize-url
Try it =)
In my project written in JavaScript I use this regex as white list:
url.match(/^((https?|ftp):\/\/|\.{0,2}\/)/)
the only limitation is that you need to put ./ in front for files in same directory but I think I can live with that.
Using Regular Expression to prevent XSS vulnerability is becoming complicated thus hard to maintain over time while it could leave some vulnerabilities behind. Having URL validation using regular expression is helpful in some scenarios but better not be mixed with vulnerability checks.
Solution probably is to use combination of an encoder like AntiXssEncoder.UrlEncode for encoding Query portion of the URL and QueryBuilder for the rest:
public sealed class AntiXssUrlEncoder
{
public string EncodeUri(Uri uri, bool isEncoded = false)
{
// Encode the Query portion of URL to prevent XSS attack if is not already encoded. Otherwise let UriBuilder take care code it.
var encodedQuery = isEncoded ? uri.Query.TrimStart('?') : AntiXssEncoder.UrlEncode(uri.Query.TrimStart('?'));
var encodedUri = new UriBuilder
{
Scheme = uri.Scheme,
Host = uri.Host,
Path = uri.AbsolutePath,
Query = encodedQuery.Trim(),
Fragment = uri.Fragment
};
if (uri.Port != 80 && uri.Port != 443)
{
encodedUri.Port = uri.Port;
}
return encodedUri.ToString();
}
public static string Encode(string uri)
{
var baseUri = new Uri(uri);
var antiXssUrlEncoder = new AntiXssUrlEncoder();
return antiXssUrlEncoder.EncodeUri(baseUri);
}
}
You may need to include white listing to exclude some characters from encoding. That could become helpful for particular sites.
HTML Encoding the page that render the URL is another thing you may need to consider too.
BTW. Please note that encoding URL may break Web Parameter Tampering so the encoded link may appear not working as expected.
Also, you need to be careful about double encoding
P.S. AntiXssEncoder.UrlEncode was better be named AntiXssEncoder.EncodeForUrl to be more descriptive. Basically, It encodes a string for URL not encode a given URL and return usable URL.
You could use a hex code to convert the entire URL and send it to your server. That way the client would not understand the content in the first glance. After reading the content, you could decode the content URL = ? and send it to the browser.
Allowing a URL and allowing JavaScript are 2 different things.
I'm having trouble figuring out the best way to encode the POST parameters to a server call. I writing a C# client that will be served by a PHP server. I want to allow a great deal of flexibility in the parameters, so my current plan is to have a single parameter that I use JSON to encode. For example:
params = {"object":"Main","function":"doecho","params":["echothis...."]}
I'm using the C# WebRequest object and contentType of "application/x-www-form-urlencoded; charset=UTF-8". The data gets to the server and everything works as expected until I add illegal JSON characters in the data.
For example, if I use the following data, then I can't do a json_decode on it on the server side. The server appears to automatically turn the %40 into a double-quote (") when I read it with $this->getRequest()->getParams(); (Zend_Framework).
params = {"object":"Main","function":"doecho","params":["echothis%25%5d%22%40%3d%26...."]}
What is the best practice here? Do I need to base64 encode the data? Is there something obvious I'm missing with the content type or a php setting?
I have full control over the client and server, so I'd like to know what is the right/best thing to do.
While potentially any content-type can be used to upload to HTTP, there are three used in practice:
One specifically set by a given service's documentation.
application/x-www-form-urlencoded - the default used by HTML forms.
multipart/form-data - the other form used by HTML forms, required when it includes form uploads.
Due to 2 and 3 being so commonly used (as they are supported by all browser's for submitting forms), pretty much all server-side tech has things to handle them. So unless the PHP part does something strange, you should be able to use either.
application/x-www-form-urlencoded isn't appropriate for some data, but is the simplest for what it is used for. It's pretty much the same as the way query-strings are created for GET form requests, but as POST content.
Hence you want your content to be:
"params=" + Uri.EscapeDataString(paramData)
As such the first becomes:
params=%7B%22object%22%3A%22Main%22%2C%22function%22%3A%22doecho%22%2C%22params%22%3A%5B%22echothis....%22%5D%7D
And the second:
params=%7B%22object%22%3A%22Ccmes_Main%22%2C%22function%22%3A%22doecho%22%2C%22params%22%3A%5B%22echothis%2525%255d%2522%2540%253d%2526....%22%5D%7D
Both of which PHP's built-ins will turn back into the forms in your question.
My first thought was encoding it as base64. I think this should be the simplies way.
From arcanecode.com:
static public string EncodeTo64(string toEncode)
{
byte[] toEncodeAsBytes = System.Text.ASCIIEncoding.ASCII.GetBytes(toEncode);
string returnValue = System.Convert.ToBase64String(toEncodeAsBytes);
return returnValue;
}
I have an MVC 3 web application project, and in one page I use NicEdit to allow the user enter formatted text.
When the controller receives the data, the data is in html format... perfect. NicEdit itself don't allow for script tags, nor onFoo events to be entered directly in elements, but one user with bad intentions can force scripts in and that would not be safe.
What can I do to ensure the safety of the incoming data... strip out script tags, find and remove onXyz events... what else?
Also, what is the easiest way to do it? Should I use HtmlAgilityPack, or there is a simple function somewhere that will do all the job with a simple call.
Note: just encoding the whole string is not a valid solution. What I want is a way to ensure that the Html code is safe to render in another page, when someone wants to view the submited content.
Thanks!
You could use the AntiXss library. Dangerous scripts will be removed:
string input = ...
string safeOutput = AntiXss.GetSafeHtmlFragment(input);
I'm not sure if I understand this code or if I'm using it right, but I was under the impression that in an ASP.NET 2.0 AJAX website I could run javascript like:
var c = Sys.CultureInfo.CurrentCulture
and it would give me the culture/language settings the user had specified in their browser at the time of the visit. However, for me, it always comes back 'en-US' no matter what language I pick in firefox or IE.
This serverside code however:
string[] languages = HttpContext.Current.Request.UserLanguages;
if (languages == null || languages.Length == 0)
return null;
try
{
string language = languages[0].ToLowerInvariant().Trim();
return CultureInfo.CreateSpecificCulture(language);
}
catch (ArgumentException)
{
return null;
}
does return the language I have currently set. But I need to do this clientside, because I need to parse a string into a datetime and do some validations before I postback, and the string could be a MM/DD/YYYY or DD/MM/YYYY, or some other such thing.
What am I missing?
EDIT:
Ok, I came across this library http://www.datejs.com/. It looks pretty sweet, and it has ninjas, so I'm pretty much sold already. But in their doc I noticed that you need to include one of the language specific js files to include. I imagine you'd have to make that determination serverside and emit the proper script include tag, which got me thinking. Am I supposed to be doing this with the ASP.NET AJAX stuff? i.e. checking the serverside culture(which works) and setting the Sys.CultureInfo.CurrentCulture in js based on that? I was hoping it would just automagically get it from the browser clientside.
The value of Sys.CultureInfo.CurrentCulture is based on a value that is sent from the server. To get the server to send the correct value back to the client, you need to set the EnableScriptGlobalization property to true on the ScriptManager object (it's false by default).
TMK, the browser does not pass any timezone info to server in the first request. You need to do this with Javascript