I'm having a problem with asp.net request validation. I have a basic page with a search field and a button. If the user inputs some illegal characters in the search field and clicks the button then of course I can validate his input in JS and everything's OK. However I have also a lot of LinkButtons not associated with the search functionality that do postbacks and when it happens I get the YSOD.
I know you can turn this feature off by adding ValidateRequest="false" in page directives or web.config, however I'd like to know if there is better and more elegant solution than simply disabling request validation completely.
Thanks.
you can use anti XSS Library to avoid cross scripting attack. check for this link AntiXSS asp.net .
and you can turn of the Yellowscreen of Death. by changing the CustomError mode to Remoteonly. so that remote user wont see the YSOD. only local server will see the YSOD
in web.config add line like this.
<configuration>
<system.web>
<customErrors defaultRedirect="yourErrorPage.html"
mode="RemoteOnly">
</customErrors>
</system.web>
</configuration>
Sounds to me like you need to put validation groups against your form elements (could be I'm misunderstanding the question).
(This would be easier if you'd have posted some code)
<asp:Panel runat="server" DefaultButton="btnSearch">
<asp:TextBox runat="server" ID="txtSearch" />
<asp:RequiredFieldValidator runat="server" ControlToValidate="txtSearch" ValidationGroup="vgSearch" ErrorMessage="Search is required!" />
<asp:Button runat="server" ID="btnSearch" ValidationGroup="vgSearch" Text="Search" />
</asp:Panel>
<asp:LinkButton runat="server" ID="btnLogin" Text="Login" ValidationGroup="vgLogin" />
<asp:LinkButton runat="server" ID="btnCakes" Text="Cakes!" ValidationGroup="vgCakes" />
Anyway, the idea is that your search form and associated validators have one validation group, and your other buttons have other validation groups, then the validator won't fire when you click another button.
I'm not actually sure if you NEED the validation groups against individual link buttons, I don't think you do, but I'm putting 'em in there to demonstrate my point.
If I've completely missed the boat, let me know :)
EDIT:
I should mention that I've just thrown the above code together, can't guarantee it's all formatted correctly, etc, etc.
Oddly enough, the day after I attempted to answer this, a co-worked asked me to help with the same problem, so here's what I'm up to so far...
(Bare in mind that while I've been developing in .Net for a number of years, I've never had need to delve that deeply into the page life cycle, ViewState or any of the hideously complicated bits that keep better dev's up at night)
Initially, I thought that overriding the PostBack event in JavaScript would allow me to edit the form post and remove the offending characters, so I tried it with a simple alert, but the potentially dangerous Request.Form was still appearing, so whatever's causing it is happening before the PostBack event is being fired.
So, after investigating the page life cycle, overriding every method I could and doing a whole lot of debugging, I found that the error is being throw in the DeterminePostBackMode method.
Now, by my understanding, this method looks at the form post and converts it to a NameValueCollection, so I built my own NameValueCollection, stripping out the "<" character (I only tested with that character to start with).
Protected Overrides Function DeterminePostBackMode() As System.Collections.Specialized.NameValueCollection
Dim stream As New System.IO.StreamReader(Request.InputStream)
Dim nvCollection As New System.Collections.Specialized.NameValueCollection()
Dim _split() As String = stream.ReadToEnd().Split("&")
If _split.Length > 1 Then
For i As Integer = 0 To _split.Length - 1
Dim kv() As String = _split(i).Split("=")
Dim _key As String = HttpUtility.UrlDecode(kv(0))
Dim _value As String = HttpUtility.UrlDecode(kv(1))
If _value.Contains("<") Then _value = ""
nvCollection.Add(_key, _value)
Next
End If
'For Each s As String In nvCollection
' Response.Write(String.Format("<p>{0}={1}</p>", s, nvCollection(s)))
'Next
Return nvCollection
End Function
And that worked brilliantly, the offending value was being stripped out and the NameValueCollection was being returned without causing an error...
Except I was still seeing the error message.
At the moment, I've tracked it to the PreInit page event, and I'm trying to figure a way around it, I'll update this as I make progress.
UPDATE:
I'm now fairly sure that the issue ISN'T with the values being stored in the ViewState. After reading this excellent article on ViewState, I tried setting the value of a TextBox to "<script" declaratively, which means it shouldn't be stored in the ViewState, which means that the error isn't caused by processing being carried out on the ViewState.
I think.
I've got a custom menu navigation built from a web.sitemap file, the first line of this would be something like:
SiteMapNodeCollection topLevelNodes = SiteMap.RootNode.ChildNodes;
This works - it gets all the top level nodes from the web.sitemap file, and allows me to look through each SiteMapNode and do stuff.
However, now I want to be able to create multiple web.sitemap files, and then programmatically determine which web.sitemap file to use, but I can't seem to find out how to do this. I'm assuming I could either create one custom SiteMapProvider that can perform the logic to determine which web.sitemap file to load, or I have multiple providers, each one with the SiteMapFile property set to a specific *.sitemap file, and then switch providers programmatically before I access SiteMap.RootNode.
I think it's probably easier to have one custom provider, and then override the part where it looks for the actual physical sitemap file location, but I'm unclear how I would do this
I've googled a lot, but most answers seem to be regarding the standard sitemappath controls and so on, and how to set a SiteMapDataSource, which I don't think is relevant to my approach.
First you need to specify all of your sitemap files in your web.config as such:
<siteMap defaultProvider="FNDSiteMap" enabled="true">
<providers>
<add name="FNDSiteMap" type="System.Web.XmlSiteMapProvider" siteMapFile="FND.sitemap" securityTrimmingEnabled="true"/>
<add name="STASiteMap" type="System.Web.XmlSiteMapProvider" siteMapFile="STA.sitemap" securityTrimmingEnabled="true"/>
<add name="TASiteMap" type="System.Web.XmlSiteMapProvider" siteMapFile="TA.sitemap" securityTrimmingEnabled="true"/>
</providers>
</siteMap>
Then in your code-behind you can dynamically assign your SiteMapDataSource (which is bound to your menu) to one of the providers you specified in your web.config:
.aspx
<asp:Menu ID="MenuLevel1" runat="server" Orientation="Horizontal" DataSourceID="SiteMapLevel1"
MaximumDynamicDisplayLevels="0" IncludeStyleBlock="false">
</asp:Menu>
<asp:SiteMapDataSource ID="SiteMapLevel1" runat="server" />
.cs
SiteMapLevel1.SiteMapProvider = "TASiteMap";
Pauli's comment was the answer to my particular requirement:
"You shouldn't switch/change anything... instead you need to access
the RootNode like this all the time
SiteMap.Providers[someProvider].RootNode and the someProvider should
then be resolved at runtime."
I hadn't realised this was possible, but was the correct solution for me.
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There are always features that would be useful in fringe scenarios, but for that very reason most people don't know them. I am asking for features that are not typically taught by the text books.
What are the ones that you know?
While testing, you can have emails sent to a folder on your computer instead of an SMTP server. Put this in your web.config:
<system.net>
<mailSettings>
<smtp deliveryMethod="SpecifiedPickupDirectory">
<specifiedPickupDirectory pickupDirectoryLocation="c:\Temp\" />
</smtp>
</mailSettings>
</system.net>
If you place a file named app_offline.htm
in the root of a web application directory, ASP.NET 2.0+ will shut-down the application and stop normal processing any new incoming requests for that application, showing only the contents of the app_offline.htm file for all new requests.
This is the quickest and easiest way to display your "Site Temporarily Unavailable" notice while re-deploying (or rolling back) changes to a Production server.
Also, as pointed out by marxidad, make sure you have at least 512 bytes of content within the file so IE6 will render it correctly.
throw new HttpException(404, "Article not found");
This will be caught by ASP.NET which will return the customErrors page. Learned about this one in a recent .NET Tip of the Day Post
Here's the best one. Add this to your web.config for MUCH faster compilation. This is post 3.5SP1 via this QFE.
<compilation optimizeCompilations="true">
Quick summary: we are introducing a
new optimizeCompilations switch in
ASP.NET that can greatly improve the
compilation speed in some scenarios.
There are some catches, so read on for
more details. This switch is
currently available as a QFE for
3.5SP1, and will be part of VS 2010.
The ASP.NET compilation system takes a
very conservative approach which
causes it to wipe out any previous
work that it has done any time a ‘top
level’ file changes. ‘Top level’ files
include anything in bin and App_Code,
as well as global.asax. While this
works fine for small apps, it becomes
nearly unusable for very large apps.
E.g. a customer was running into a
case where it was taking 10 minutes to
refresh a page after making any change
to a ‘bin’ assembly.
To ease the pain, we added an
‘optimized’ compilation mode which
takes a much less conservative
approach to recompilation.
Via here:
HttpContext.Current will always give you access to the current context's Request/Response/etc., even when you don't have access to the Page's properties (e.g., from a loosely-coupled helper class).
You can continue executing code on the same page after redirecting the user to another one by calling Response.Redirect(url, false )
You don't need .ASPX files if all you want is a compiled Page (or any IHttpHandler). Just set the path and HTTP methods to point to the class in the <httpHandlers> element in the web.config file.
A Page object can be retrieved from an .ASPX file programmatically by calling PageParser.GetCompiledPageInstance(virtualPath,aspxFileName,Context)
Retail mode at the machine.config level:
<configuration>
<system.web>
<deployment retail="true"/>
</system.web>
</configuration>
Overrides the web.config settings to enforce debug to false, turns custom errors on and disables tracing. No more forgetting to change attributes before publishing - just leave them all configured for development or test environments and update the production retail setting.
Enabling intellisense for MasterPages in the content pages
I am sure this is a very little known hack
Most of the time you have to use the findcontrol method and cast the controls in master page from the content pages when you want to use them, the MasterType directive will enable intellisense in visual studio once you to this
just add one more directive to the page
<%# MasterType VirtualPath="~/Masters/MyMainMasterPage.master" %>
If you do not want to use the Virtual Path and use the class name instead then
<%# MasterType TypeName="MyMainMasterPage" %>
Get the full article here
HttpContext.Items as a request-level caching tool
Two things stand out in my head:
1) You can turn Trace on and off from the code:
#ifdef DEBUG
if (Context.Request.QueryString["DoTrace"] == "true")
{
Trace.IsEnabled = true;
Trace.Write("Application:TraceStarted");
}
#endif
2) You can build multiple .aspx pages using only one shared "code-behind" file.
Build one class .cs file :
public class Class1:System.Web.UI.Page
{
public TextBox tbLogin;
protected void Page_Load(object sender, EventArgs e)
{
if (tbLogin!=null)
tbLogin.Text = "Hello World";
}
}
and then you can have any number of .aspx pages (after you delete .designer.cs and .cs code-behind that VS has generated) :
<%# Page Language="C#" AutoEventWireup="true" Inherits="Namespace.Class1" %>
<form id="form1" runat="server">
<div>
<asp:TextBox ID="tbLogin" runat="server"></asp: TextBox >
</div>
</form>
You can have controls in the ASPX that do not appear in Class1, and vice-versa, but you need to remeber to check your controls for nulls.
You can use:
Request.Params[Control.UniqueId]
To get the value of a control BEFORE viewstate is initialized (Control.Text etc will be empty at this point).
This is useful for code in Init.
WebMethods.
You can using ASP.NET AJAX callbacks to web methods placed in ASPX pages. You can decorate a static method with the [WebMethod()] and [ScriptMethod()] attributes. For example:
[System.Web.Services.WebMethod()]
[System.Web.Script.Services.ScriptMethod()]
public static List<string> GetFruitBeginingWith(string letter)
{
List<string> products = new List<string>()
{
"Apple", "Banana", "Blackberry", "Blueberries", "Orange", "Mango", "Melon", "Peach"
};
return products.Where(p => p.StartsWith(letter)).ToList();
}
Now, in your ASPX page you can do this:
<form id="form1" runat="server">
<div>
<asp:ScriptManager ID="ScriptManager1" runat="server" EnablePageMethods="true" />
<input type="button" value="Get Fruit" onclick="GetFruit('B')" />
</div>
</form>
And call your server side method via JavaScript using:
<script type="text/javascript">
function GetFruit(l)
{
PageMethods.GetFruitBeginingWith(l, OnGetFruitComplete);
}
function OnGetFruitComplete(result)
{
alert("You got fruit: " + result);
}
</script>
Check to see if the client is still connected, before starting a long-running task:
if (this.Response.IsClientConnected)
{
// long-running task
}
One little known and rarely used feature of ASP.NET is:
Tag Mapping
It's rarely used because there's only a specific situation where you'd need it, but when you need it, it's so handy.
Some articles about this little know feature:
Tag Mapping in ASP.NET
Using Tag Mapping in ASP.NET 2.0
and from that last article:
Tag mapping allows you to swap
compatible controls at compile time on
every page in your web application. A
useful example is if you have a stock
ASP.NET control, such as a
DropDownList, and you want to replace
it with a customized control that is
derived from DropDownList. This could
be a control that has been customized
to provide more optimized caching of
lookup data. Instead of editing every
web form and replacing the built in
DropDownLists with your custom
version, you can have ASP.NET in
effect do it for you by modifying
web.config:
<pages>
<tagMapping>
<clear />
<add tagType="System.Web.UI.WebControls.DropDownList"
mappedTagType="SmartDropDown"/>
</tagMapping>
</pages>
HttpModules. The architecture is crazy elegant. Maybe not a hidden feature, but cool none the less.
You can use ASP.NET Comments within an .aspx page to comment out full parts of a page including server controls. And the contents that is commented out will never be sent to the client.
<%--
<div>
<asp:Button runat="server" id="btnOne"/>
</div>
--%>
The Code Expression Builder
Sample markup:
Text = '<%$ Code: GetText() %>'
Text = '<%$ Code: MyStaticClass.MyStaticProperty %>'
Text = '<%$ Code: DateTime.Now.ToShortDateString() %>'
MaxLenth = '<%$ Code: 30 + 40 %>'
The real beauty of the code expression builder is that you can use databinding like expressions in non-databinding situations. You can also create other Expression Builders that perform other functions.
web.config:
<system.web>
<compilation debug="true">
<expressionBuilders>
<add expressionPrefix="Code" type="CodeExpressionBuilder" />
The cs class that makes it all happen:
[ExpressionPrefix("Code")]
public class CodeExpressionBuilder : ExpressionBuilder
{
public override CodeExpression GetCodeExpression(
BoundPropertyEntry entry,
object parsedData,
ExpressionBuilderContext context)
{
return new CodeSnippetExpression(entry.Expression);
}
}
Usage of the ASHX file type:
If you want to just output some basic html or xml without going through the page event handlers then you can implement the HttpModule in a simple fashion
Name the page as SomeHandlerPage.ashx and just put the below code (just one line) in it
<%# webhandler language="C#" class="MyNamespace.MyHandler" %>
Then the code file
using System;
using System.IO;
using System.Web;
namespace MyNamespace
{
public class MyHandler: IHttpHandler
{
public void ProcessRequest (HttpContext context)
{
context.Response.ContentType = "text/xml";
string myString = SomeLibrary.SomeClass.SomeMethod();
context.Response.Write(myString);
}
public bool IsReusable
{
get { return true; }
}
}
}
Setting Server Control Properties Based on Target Browser and more.
<asp:Label runat="server" ID="labelText"
ie:Text="This is IE text"
mozilla:Text="This is Firefox text"
Text="This is general text"
/>
That one kinda took me by surprise.
System.Web.VirtualPathUtility
I worked on a asp.net application which went through a security audit by a leading security company and I learned this easy trick to preventing a lesser known but important security vulnerability.
The below explanation is from:
http://www.guidanceshare.com/wiki/ASP.NET_2.0_Security_Guidelines_-_Parameter_Manipulation#Consider_Using_Page.ViewStateUserKey_to_Counter_One-Click_Attacks
Consider using Page.ViewStateUserKey to counter one-click attacks. If you authenticate your callers and use ViewState, set the Page.ViewStateUserKey property in the Page_Init event handler to prevent one-click attacks.
void Page_Init (object sender, EventArgs e) {
ViewStateUserKey = Session.SessionID;
}
Set the property to a value you know is unique to each user, such as a session ID, user name, or user identifier.
A one-click attack occurs when an attacker creates a Web page (.htm or .aspx) that contains a hidden form field named __VIEWSTATE that is already filled with ViewState data. The ViewState can be generated from a page that the attacker had previously created, such as a shopping cart page with 100 items. The attacker lures an unsuspecting user into browsing to the page, and then the attacker causes the page to be sent to the server where the ViewState is valid. The server has no way of knowing that the ViewState originated from the attacker. ViewState validation and HMACs do not counter this attack because the ViewState is valid and the page is executed under the security context of the user.
By setting the ViewStateUserKey property, when the attacker browses to a page to create the ViewState, the property is initialized to his or her name. When the legitimate user submits the page to the server, it is initialized with the attacker's name. As a result, the ViewState HMAC check fails and an exception is generated.
HttpContext.Current.IsDebuggingEnabled
This is great for determining which scripts to output (min or full versions) or anything else you might want in dev, but not live.
Included in ASP.NET 3.5 SP1:
customErrors now supports "redirectMode" attribute with a value of "ResponseRewrite". Shows error page without changing URL.
The form tag now recognizes the action attribute. Great for when you're using URL rewriting
DefaultButton property in Panels.
It sets default button for a particular panel.
ScottGu has a bunch of tricks at http://weblogs.asp.net/scottgu/archive/2006/04/03/441787.aspx
Using configSource to split configuration files.
You can use the configSource attribute in a web.config file to push configuration elements to other .config files, for example,
instead of:
<appSettings>
<add key="webServiceURL" value="https://some/ws.url" />
<!-- some more keys -->
</appSettings>
...you can have the entire appSettings section stored in another configuration file. Here's the new web.config :
<appSettings configSource="myAppSettings.config" />
The myAppSettings.config file :
<appSettings>
<add key="webServiceURL" value="https://some/ws.url" />
<!-- some more keys -->
</appSettings>
This is quite useful for scenarios where you deploy an application to a customer and you don't want them interfering with the web.config file itself and just want them to be able to change just a few settings.
ref: http://weblogs.asp.net/fmarguerie/archive/2007/04/26/using-configsource-to-split-configuration-files.aspx
MaintainScrollPositionOnPostback attribute in Page directive. It is used to maintain scroll position of aspx page across postbacks.
HttpContext.IsCustomErrorEnabled is a cool feature.I've found it useful more than once. Here is a short post about it.
By default, any content between tags for a custom control is added as a child control. This can be intercepted in an AddParsedSubObject() override for filtering or additional parsing (e.g., of text content in LiteralControls):
protected override void AddParsedSubObject(object obj)
{ var literal = obj as LiteralControl;
if (literal != null) Controls.Add(parseControl(literal.Text));
else base.AddParsedSubObject(obj);
}
...
<uc:MyControl runat='server'>
...this text is parsed as a LiteralControl...
</uc:MyControl>
If you have ASP.NET generating an RSS feed, it will sometimes put an extra line at the top of the page. This won't validate with common RSS validators. You can work around it by putting the page directive <#Page> at the bottom of the page.
Before ASP.NET v3.5 added routes you could create your own friendly URLs simply by writing an HTTPModule to and rewrite the request early in the page pipeline (like the BeginRequest event).
Urls like http://servername/page/Param1/SomeParams1/Param2/SomeParams2 would get mapped to another page like below (often using regular expressions).
HttpContext.RewritePath("PageHandler.aspx?Param1=SomeParms1&Param2=SomeParams2");
DotNetNuke has a really good HttpModule that does this for their friendly urls. Is still useful for machines where you can't deploy .NET v3.5.