Scott Hanselman

ASP.NET - Overposting/Mass Assignment Model Binding Security

April 19, '17 Comments [41] Posted in ASP.NET | ASP.NET MVC
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imageThis little post is just a reminder that while Model Binding in ASP.NET is very cool, you should be aware of the properties (and semantics of those properties) that your object has, and whether or not your HTML form includes all your properties, or omits some.

OK, that's a complex - and perhaps poorly written - sentence. Let me back up.

Let's say you have this horrible class. Relax, yes, it's horrible. It's an example. It'll make sense in a moment.

public class Person
{
public int ID { get; set; }
public string First { get; set; }
public string Last { get; set; }
public bool IsAdmin { get; set; }
}

Then you've got an HTML Form in your view that lets folks create a Person. That form has text boxes/fields for First, and Last. ID is handled by the database on creation, and IsAdmin is a property that the user doesn't need to know about. Whatever. It's secret and internal. It could be Comment.IsApproved or Product.Discount. You get the idea.

Then you have a PeopleController that takes in a Person via a POST:

[HttpPost]
[ValidateAntiForgeryToken]
public async Task<IActionResult> Create(Person person)
{
if (ModelState.IsValid)
{
_context.Add(person);
await _context.SaveChangesAsync();
return RedirectToAction("Index");
}
return View(person);
}

If a theoretical EvilUser found out that Person had an "IsAdmin" property, they could "overpost" and add a field to the HTTP POST and set IsAdmin=true. There's nothing in the code here to prevent that. ModelBinding makes your code simpler by handling the "left side -> right side" boring code of the past. That was all that code where you did myObject.Prop = Request.Form["something"]. You had lines and lines of code digging around in the QueryString or Form POST.

Model Binding gets rid of that and looks at the properties of the object and lines them up with HTTP Form POST name/value pairs of the same names.

NOTE: Just a friendly reminder that none of this "magic" is magic or is secret. You can even write your own custom model binders if you like.

The point here is that folks need to be aware of the layers of abstraction when you use them. Yes, it's convenient, but it's hiding something from you, so you should know the side effects.

How do we fix the problem? Well, a few ways. You can mark the property as [ReadOnly]. More commonly, you can use a BindAttribute on the method parameters and just include (whitelist) the properties you want to allow for binding:

public async Task<IActionResult> Create([Bind("First,Last")] Person person)

Or, the correct answer. Don't let models that look like this get anywhere near the user. This is the case for ViewModels. Make a model that looks like the View. Then do the work. You can make the work easier with something like AutoMapper.

Some folks find ViewModels to be too cumbersome for basic stuff. That's valid. There are those that are "All ViewModels All The Time," but I'm more practical. Use what works, use what's appropriate, but know what's happening underneath so you don't get some scriptkiddie overposting to your app and a bit getting flipped in your Model as a side effect.

Use ViewModels when possible or reasonable, and when not, always whitelist your binding if the model doesn't line up one to one (1:1) with your HTML Form.

What are your thoughts?


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About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Options for CSS and JS Bundling and Minification with ASP.NET Core

March 18, '17 Comments [16] Posted in ASP.NET | DotNetCore
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Maria and I were updating the NerdDinner sample app (not done yet, but soon) and were looking at various ways to do bundling and minification of the JSS and CS. There's runtime bundling on ASP.NET 4.x but in recent years web developers have used tools like Grunt or Gulp to orchestrate a client-side build process to squish their assets. The key is to find a balance that gives you easy access to development versions of JS/CSS assets when at dev time, while making it "zero work" to put minified stuff into production. Additionally, some devs don't need the Grunt/Gulp/npm overhead while others absolutely do. So how do you find balance? Here's how it works.

I'm in Visual Studio 2017 and I go File | New Project | ASP.NET Core Web App. Bundling isn't on by default but the configuration you need IS included by default. It's just minutes to enable and it's quite nice.

In my Solution Explorer is a "bundleconfig.json" like this:

// Configure bundling and minification for the project.
// More info at https://go.microsoft.com/fwlink/?LinkId=808241
[
{
"outputFileName": "wwwroot/css/site.min.css",
// An array of relative input file paths. Globbing patterns supported
"inputFiles": [
"wwwroot/css/site.css"
]
},
{
"outputFileName": "wwwroot/js/site.min.js",
"inputFiles": [
"wwwroot/js/site.js"
],
// Optionally specify minification options
"minify": {
"enabled": true,
"renameLocals": true
},
// Optionally generate .map file
"sourceMap": false
}
]

Pretty simple. Ins and outs. At the top of the VS editor you'll see this yellow prompt. VS knows you're in a bundleconfig.json and in order to use it effectively in VS you grab a small extension. To be clear, it's NOT required. It just makes it easier. The source is at https://github.com/madskristensen/BundlerMinifier. Slip this UI section if you just want Build-time bundling.

BundleConfig.json

If getting a prompt like this bugs you, you can turn all prompting off here:

Tools Options HTML Advanced Identify Helpful Extensions

Look at your Solution Explorer. See under site.css and site.js? There are associated minified versions of those files. They aren't really "under" them. They are next to them on the disk, but this hierarchy is a nice way to see that they are associated, and that one generates the other.

Right click on your project and you'll see this Bundler & Minifier menu:

Bundler and Minifier Menu

You can manually update your Bundles with this item as well as see settings and have bundling show up in the Task Runner Explorer.

Build Time Minification

The VSIX (VS extension) gives you the small menu and some UI hooks, but if you want to have your bundles updated at build time (useful if you don't use VS!) then you'll want to add a NuGet package called BuildBundlerMinifier.

You can add this NuGet package SEVERAL ways. Which is awesome.

  • Add it from the Manage NuGet Packages menu
  • Add it from the command line via "dotnet add package BuildBundlerMinifier"
    • Note that this adds it to your csproj without you having to edit it! It's like "nuget install" but adds references to projects!  The dotnet CLI is lovely.
  • If you have the VSIX installed, just right-click the bundleconfig.json and click "Enable bundle on build..." and you'll get the NuGet package.
    Enable bundle on build

Now bundling will run on build...

c:\WebApplication8\WebApplication8>dotnet build
Microsoft (R) Build Engine version 15
Copyright (C) Microsoft Corporation. All rights reserved.

Bundler: Begin processing bundleconfig.json
Bundler: Done processing bundleconfig.json
WebApplication8 -> c:\WebApplication8\bin\Debug\netcoreapp1.1\WebApplication8.dll

Build succeeded.
0 Warning(s)
0 Error(s)

...even from the command line with "dotnet build." It's all integrated.

This is nice for VS Code or users of other editors. Here's how it would work entirely from the command prompt:

$ dotnet new mvc
$ dotnet add package BuildBundlerMinifier
$ dotnet restore
$ dotnet run

Advanced: Using Gulp to handle Bundling/Minifying

If you outgrow this bundler or just like Gulp, you can right click and Convert to Gulp!

Convert to Gulp

Now you'll get a gulpfile.js that uses the bundleconfig.json and you've got full control:

gulpfile.js

And during the conversion you'll get the npm packages you need to do the work automatically:

npm and bower

I've found this to be a good balance that can get quickly productive with a project that gets bundling without npm/node, but I can easily grow to a larger, more npm/bower/gulp-driven front-end developer-friendly app.


Sponsor: Did you know VSTS can integrate closely with Octopus Deploy? Join Damian Brady and Brian A. Randell as they show you how to automate deployments from VSTS to Octopus Deploy, and demo the new VSTS Octopus Deploy dashboard widget. Register now!

About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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ZEIT now deployments of open source ASP.NET Core web apps with Docker

March 15, '17 Comments [14] Posted in ASP.NET | Docker | DotNetCore
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ZEIT is a new cloud service and "now" is the name of their deployment tool. ZEIT World is their DNS service. If you head over to https://zeit.co/ you'll see a somewhat cryptic animated gif that shows how almost impossibly simple it is to deploy a web app with ZEIT now.

ZEIT works with .NET Core and ASP.NET

You can make a folder, put an index.html (for example) in it and just run "now." You'll automatically get a website with an autogenerated name and it'll be live. It's probably the fastest and easiest deploy I've ever seen. Remember when Heroku (then Azure, then literally everyone) started using git for deployment? Clearly being able to type "now" and just get a web site on the public internet was the next step. (Next someone will make "up" which will then get replaced with just pressing ENTER on an empty line! ;) )

Jokes aside, now is clean and easy. I appreciate their organizational willpower to make an elegant and simple command line tool. I suspect it's harder than it looks to keep things simple.

All of their examples use JavaScript and node.js, but they also support Docker, which means they support open source ASP.NET Core on .NET Core! But do they know they do? ;) Let's find out.

And more importantly, how easy is it? Can I take a site from concept to production in minutes? Darn tootin' I can.

First, make a quick ASP.NET Core app. I'll use the MVC template with Bootstrap.

C:\Users\scott\zeitdotnet>dotnet new mvc
Content generation time: 419.5337 ms
The template "ASP.NET Core Web App" created successfully.

I'll do a quick dotnet restore to get the packages for my project.

C:\Users\scott\zeitdotnet>dotnet restore
Restoring packages for C:\Users\scott\zeitdotnet\zeitdotnet.csproj...
Generating MSBuild file C:\Users\scott\zeitdotnet\obj\zeitdotnet.csproj.nuget.g.props.
Generating MSBuild file C:\Users\scott\zeitdotnet\obj\zeitdotnet.csproj.nuget.g.targets.
Writing lock file to disk. Path: C:\Users\scott\zeitdotnet\obj\project.assets.json
Restore completed in 2.93 sec for C:\Users\scott\zeitdotnet\zeitdotnet.csproj.

NuGet Config files used:
C:\Users\scott\AppData\Roaming\NuGet\NuGet.Config
C:\Program Files (x86)\NuGet\Config\Microsoft.VisualStudio.Offline.config

Feeds used:
https://api.nuget.org/v3/index.json
C:\LocalNuGet
C:\Program Files (x86)\Microsoft SDKs\NuGetPackages\

Now I need to add a Dockerfile. I'll make one in the root that looks like this:

FROM microsoft/aspnetcore
LABEL name="zeitdotnet"
ENTRYPOINT ["dotnet", "zeitdotnet.dll"]
ARG source=.
WORKDIR /app
EXPOSE 80
COPY $source .

Note that I could have ZEIT build my app for me if I used the aspnetcore Dockerfile that includes the .NET Core SDK, but that would not only make my deployment longer, it would also make my docker images a LOT larger. I want to include JUST the .NET Core runtime in my image, so I'll build and publish locally.

ZEIT now is going to need to see my Dockerfile, and since I want my app to include the binaries (I don't want to ship my source in the Docker image up to ZEIT) I need to mark my Dockerfile as "Content" and make sure it's copied to the publish folder when my app is built and published.

<ItemGroup>
  <None Remove="Dockerfile" />
</ItemGroup>

<ItemGroup>
  <Content Include="Dockerfile">
    <CopyToOutputDirectory>Always</CopyToOutputDirectory>
  </Content>
</ItemGroup>

I'll add this my project's csproj file. If I was using Visual Studio, this is the same as right clicking on the Properties of the Dockerfile, setting it to Content and then "Always Copy to Output Directory."

Now I'll just build and publish to a folder with one command:

C:\Users\scott\zeitdotnet>dotnet publish
Microsoft (R) Build Engine version 15.1.548.43366
Copyright (C) Microsoft Corporation. All rights reserved.

zeitdotnet -> C:\Users\scott\zeitdotnet\bin\Debug\netcoreapp1.1\zeitdotnet.dll

And finally, from the .\bin\Debug\netcoreapp1.1\ folder I run "now." (Note that I've installed now and signed up for their service, of course.)

C:\Users\scott\zeitdotnet\bin\Debug\netcoreapp1.1\publish>now
> Deploying ~\zeitdotnet\bin\Debug\netcoreapp1.1\publish
> Ready! https://zeitdotnet-gmhcxevqkf.now.sh (copied to clipboard) [3s]
> Upload [====================] 100% 0.0s
> Sync complete (196.18kB) [2s]
> Initializing…
> Building
> ▲ docker build
> ---> 035a0a1401c3
> Removing intermediate container 289b9e4ce5d9
> Step 6 : EXPOSE 80
> ---> Running in efb817308333
> ---> fbac2aaa3039
> Removing intermediate container efb817308333
> Step 7 : COPY $source .
> ---> ff009cfc48ea
> Removing intermediate container 8d650c1867cd
> Successfully built ff009cfc48ea
> ▲ Storing image
> ▲ Deploying image
> Deployment complete!

Now has put the generated URL in my clipboard (during deployment you'll get redirected to a lovely status page) and when it's deployed I can visit my live site. But, that URL is not what I want. I want to use a custom URL.

I can take one of my domains and set it up with ZEIT World's DNS but I like DNSimple (ref).

I can add my domain as an external one after adding a TXT record to my DNS to verify I own it. Then I setup a CNAME to point my subdomain to alias.zeit.co.

C:\Users\scott\Desktop\zeitdotnet>now alias https://zeitdotnet-gmhcxevqkf.now.sh http://zeitdotnet.hanselman.com
> zeitdotnet.hanselman.com is a custom domain.
> Verifying the DNS settings for zeitdotnet.hanselman.com (see https://zeit.world for help)
> Verification OK!
> Provisioning certificate for zeitdotnet.hanselman.com
> Success! Alias created:
https://zeitdotnet.hanselman.com now points to https://zeitdotnet-gmhcxevqkf.now.sh [copied to clipboard]

And that's it. It even has a nice SSL certificate that they applied for me. It doesn't terminate to SSL all the way into the docker container's Kestral web server, but for most things that aren't banking it'll be just fine.

All in all, a lovely experience. Here's my Hello World ASP.NE Core app running in ZEIT and deployed with now  at http://zeitdotnet.hanselman.com (if you are visiting this long after this was published, this sample MAY be gone.)

I am still learning about this (this whole exercise was about 30 total minutes and asking Glenn Condron a docker question) so I'm not clear how this would work in a large multi-container deployment, but as long as your site is immutable (don't write to the container's local disk!) ZEIT says it will scale your single containers. Perhaps docker-compose support is coming?


Sponsor: Did you know VSTS can integrate closely with Octopus Deploy? Join Damian Brady and Brian A. Randell as they show you how to automate deployments from VSTS to Octopus Deploy, and demo the new VSTS Octopus Deploy dashboard widget. Register now!

About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Three FREE Training Courses on ASP.NET Core from Microsoft Virtual Academy

January 17, '17 Comments [17] Posted in ASP.NET
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This time last year we did a Microsoft Virtual Academy class on what was then called "ASP.NET 5." It made sense to call it 5 since 5 > 4.6, right? But since then ASP.NET 5 has become .NET Core 1.0 and ASP.NET Core 1.0. It's 1.0 because it's smaller, newer, and different. As the .NET "full" framework marches on, on Windows, .NET Core is cross-platform and for the cloud.

Command line concepts like dnx, dnu, and dnvm have been unified into a single "dotnet" driver. You can download .NET Core at http://dot.net and along with http://code.visualstudio.com you can get a web site up and running in 10 minutes on Windows, Mac, or many flavors of Linux.

So, we've decided to update and refresh our Microsoft Virtual Academy. In fact, we've done three days of training. Introduction, Intermediate, and Cross-Platform and all three days are now available! We just released training for ASP.NET Core 1.0 Cross-Platform that shows Mac, Ubuntu, and Docker!

Head over to Microsoft Virtual Academy and watch our new, free "Introduction to ASP.NET Core 1.0." It's a great relaxed pace if you've been out of the game for a bit, or you're a seasoned .NET "Full" developer who has avoided learning .NET Core thus far. If you don't know the C# language yet, check out our online C# tutorial first, then watch the video.

Introduction to ASP.NET Core 1.0

Join experts Scott Hanselman and Maria Naggaga, and find out how to build .NET Core applications on any operating system. Bring your web development expertise and roll up your sleeves, for this first in a three-part series.

image

Intermediate ASP.NET Core 1.0

Want a deeper dive into ASP.NET Core 1.0? Build on what you learned in Introduction to ASP.NET Core 1.0, and explore this new technology even further, as Scott Hanselman, Jeff Fritz, and Rowan Miller offer an in-depth, intermediate-level look at ASP.NET Core 1.0.

Intermediate ASP.NET Core 1.0

ASP.NET Core 1.0 Cross-Platform

Ready to build and deploy ASP.NET Core 1.0 apps? Join experts Scott Hanselman, Maria Naggaga, and Glenn Condron, and see how to do just that using Mac and Linux. Revisit content from the Introduction to ASP.NET Core 1.0 course, but using a Mac and Linux.

image

Do us a favor when you watch these, rate them (5 stars!) and SHARE them on your social networks.

NOTE: There's a LOT of quality free courseware for learning .NET Core and ASP.NET Core. We've put the best at http://asp.net/free-courses and I encourage you to check them out!

Hope you have as much fun with these courses as we had creating them!


Sponsor: Do you deploy the same application multiple times for each of your end customers? The team at Octopus have taken the pain out of multi-tenant deployments. Check out their latest 3.4 release

About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Free Intermediate ASP.NET Core 1.0 Training on Microsoft Virtual Academy

December 20, '16 Comments [3] Posted in ASP.NET
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At the end of October I announced that Maria from my team and I published a Microsoft Virtual Academy on ASP.NET Core. This Free ASP.NET Core 1.0 Training is up on Microsoft Virtual Academy now for you to watch and enjoy! I hope you like it, we worked very hard to bring it to you.

Again, start with Introduction to ASP.NET Core 1.0, and explore this new technology even further in Intermediate ASP.NET Core 1.0.

Intermediate ASP.NET Core 1.0

Intermediate ASP.NET Core 1.0

We've just launched Day 2, the Intermediate day. If the first is 100 level, this is 200 level. In this day, Jeff Fritz and I build on what we learned with Maria in Day 1. We're also joined by Rowan Miller and Maria later in the day as we explore topics like:

  • Tag Helpers
  • Authentication
  • Custom Middleware
  • Dependency Injection
  • Web APIs
  • Single Page Apps
  • Entity Framework Core and Database Access
  • Publishing and Deployment

In a few weeks (maybe sooner) we'll publish Day 3 which we'll do exclusively on Macs and Linux machines. We'll talk about Cross-Platform concerns and Containers.

NOTE: There's a LOT of quality free courseware for learning .NET Core and ASP.NET Core. We've put the best at http://asp.net/free-courses and I encourage you to check them out!

Also, please help me out by adding a few stars there under Ratings. We're new. ;)


Sponsor: Do you deploy the same application multiple times for each of your end customers? The team at Octopus have taken the pain out of multi-tenant deployments. Check out their latest 3.4 release

About Scott

Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. He is a failed stand-up comic, a cornrower, and a book author.

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Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.