I'm trying to post simple request using Flurl. But there is an exception, because takenPicture string is too large. Is there any way to post large string using Flurl?
System.UriFormatException: Uri is longer than the maximum 32766 characters.
var postData = BaseAdress.PostUrlEncodedAsync(new {
text = Uri.EscapeDataString(body),
subject = Uri.EscapeDataString(subject),
from_email = from,
recipient_email = to,
picture = takenPicture //Base64 string
});
This limitation, while a little arbitrary, is by design in Microsoft's Uri.EscapeDataString method, which is commonly used by applications and libraries (including Flurl) to encode data for both URL queries and URL-encoded request bodies. Both Xamarin and RestSharp Portable have dealt with this so I'm sure a work-around is possible and I might consider this in Flurl if you want to create an issue.
However, keep in mind that URL-encoding binary data like images is very unusual, and there are good reasons to avoid it if possible. Of course, if this is a 3rd-party API you're working with, you don't have much of a choice. But if you have control of the server-side code, I would suggest refactoring that to accept multipart/form-data instead.
In a WinForms application targeting .NET 4, I am using the WebClient.UploadValues(Uri, "POST", NameValueCollection) to send values to an instance of HttpListener. On the listener side, when the HttpListener.GetContext() method returns, I can access the sent data as a byte [].
I can convert this data to text using EncodingXXX.GetString(buffer) which returns the following:
Key1=Value1
Key2=Value2
...
Each item in the string is delimited by the ampersand sign &. I have to manually split the data into pairs and further split the pairs into keys and values.
I'd like to know if the same data can be accessed similar to ASP .NET WebForms (var value = this.Form["Key"])? Of course, I know we don't have the WebForms context here but I'd prefer to use existing infrastructure for this kind of processing wherever possible.
As per comments, I'm posting this as an answer.
I believe it should work in all cases, let me know if it doesn't, but HttpUtility.ParseQueryString(string) should be a perfect match for this.
It is, as is suggested by the name, meant for parsing URL query strings, but from what I can think, it should be a clean conversion from anything that's permissible in a datastring to anything that's permissible in a URL (of course, not vice-versa).
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.
Assume the following Url:
"http://server/application1/TestFile.aspx?Library=Testing&Filename=Documents & Functions + Properties.docx&Save=true"
I use HttpUtility.UrlEncode() to encode the value of the Filename parameter and I create the following Url:
"http://server/application1/TestFile.aspx?Library=Testing&Filename=Documents%20%26%20Functions%20%2B%20Properties.docx&Save=true"
I send the following (encoded version) of request from a client to a C# Web Application. On the server when I process the request I have a problem. The HttpRequest variable contains the query string partially decoded. That is to say when I try to use or quick watch the following properties of HttpRequest they have the following values.
Property = Value
================
HttpRequest.QueryString = "{Library=Testing&Filename=Documents+&+Functions+++Properties.docx&Save=true}"
HttpRequest.Url = "{http://server/application1/TestFile.aspx?Library=Testing&Filename=Documents & Functions + Properties.docx&Save=true}"
HttpRequest.Url.AbsoluteUri = "http://server/application1/TestFile.aspx?Library=Testing&Filename=Documents%20&%20Functions%20+%20Properties.docx&Save=true"
I have also checked the following properties but all of them have the & value decoded. However all other values remain properly encoded (e.g. space is %20).
HttpRequest.Url.OriginalString
HttpRequest.Url.Query
HttpRequest.Url.PathAndQuery
HttpRequest.RawUrl
There is no way I can read the value of the parameter Filename properly. Am I missing something?
The QueryString property returns a NameValueCollection object that maps the querystring keys to fully-decoded values.
You need to write Request.QueryString["FileName"].
I'm answering this question many years later because I just had this problem and figured out the solution. The problem is that HttpRequest.Url isn't really the value that you gave. HttpRequest.Url is a Uri class and that value is the ToString() value of that class. ToString() for the Uri class decodes the Url. Instead, what you want to use is HttpRequest.Url.OriginalString. That is the encoded version of the URL that you are looking for. Hope this helps some future person having this problem.
What happens when you don't use UrlEncode? You didn't show how exactly you are using the url that you created using UrlEncode, so it is quite possible that things are just being double encoded (lots of the framework will encode the URLs for you automatically).
FWIW I ran into this same problem with RavenDB (version 960). They implement their own HttpRequest object that behaves just like this -- it first decodes just the ampersands (from %26 to &) and then decodes the entire value. I believe this is a bug.
A couple of workarounds to this problem:
Implement your own query string parsing on the server. It's not fun but it is effective.
Double-encode ampersands. First encode just the ampersands in the string, then encode the entire string. (It's an easy solution but not extensible because it puts the burden on the client.)
I need to pass (via string content of a HTTP request/response body) name value pairs of data (like a hash) back from a Ruby on Rails server to a C# client.
Anyone happen to know offhand what would be the best format to do this in? Probably XML I would guess?
tks
PS. So overall the requirement is find a C# method that convert from a String of name/value pairs in JSON format (created by Ruby/Rails) to an existing C# standard name/value pair class/variable (e.g. Array or Dictionary I guess?)
You could to post that data as:
HTTP POST fields (read it with Request.Form)
HTTP POST field with XML (Request.Form, XmlDocument)
HTTP POST field with JSON data (DataContractJsonSerializer)
EDIT: I have this samples:
// Building on Silverlight to send
using (MemoryStream ms = new MemoryStream())
{
new DataContractJsonSerializer(fileList.GetType()).WriteObject(ms, fileList);
// send it
}
// Reading on ASHX page
JobEntry[] files =
new JavaScriptSerializer().Deserialize<Negocio.Cache.JobEntry[]>(
new StreamReader(context.Request.InputStream).ReadToEnd());
Actually, JSON is supported in both, and would certainly do what you require.
Here are links to a Javascript Serializer for C#: Parsing JSON using Json.net
And as long as you require 'json' for Ruby on Rails, you can simply use the "[to_json]"1 method.