Search for a command to run...
Wesley is a Coding Architect at Xebia in Belgium, where he helps organizations to build better applications, helps teams to improve their skills and organizes workshops to share his knowledge. He's also a Microsoft Azure MVP, board member of the VISUG meetup in Belgium and speaker at conferences and meetups.
Chances are high that if you’re building a Web API, you’re relying on access tokens when client applications or services interact with your API in order to perform authentication and authorization. The two most common types of access tokens are opaqu...
Account enumeration is the process where someone attempts to find out which accounts are valid users in a system, by using typically the login, registration or password reset pages of a system in a way that it wasn't designed for. The most basic exam...
Recently, I had to pass around some data between two HTTP requests in an ASP.NET Core project. Because this data could be interesting to retain during the user's session, I stored it in HttpContext.Session which was configured in the Startup class an...
When I read Ken's blog post about an issue he had with a certain class in a project he is working on, his solution didn't sit quite right with me. I know that in Ken's case, the code couldn't be improved any further because of dependencies on other b...
Welcome back for my second post about debugging! In this post, I'll give you an overview of the basic capabilities of the debugger in Visual Studio 2015, and add a few tips and tricks to take your debugging skills to the next level. We will not delve...
CSP, or Content Security Policy, is an added layer of security that helps to detect and mitigate certain types of attacks, including Cross-Site Scripting (XSS) and data injection attacks. In short, you can add this policy using either a <meta> tag or by setting additional headers in your HTTP response, and using the policy you'll limit the origins for resources for that HTTP request. For example:
script-src 'self' allows loading scripts from the current domainchild-src https://youtube.com allows the use of <iframe> tags pointing towards YouTubestyle-src 'self' https://maxcdn.bootstrapcdn.com allows loading CSS files from the current source and from a CDN.If you want to read up on CSP, I suggest heading over to http://www.html5rocks.com/en/tutorials/security/content-security-policy/.
Now, I was trying out some things concerning CSP and inline scripts. You could add 'unsafe-inline' to the script-src source list to allow all inline scripting (except eval and other bad stuff, you need 'unsafe-eval' in that case), but that is exactly what you would want to avoid. Instead, you can opt to do one of these things:
<script src=""></script> tags, while adding 'self' to script-src if that wasn't already the case. The easiest solution, but not always possible.Options 2 and 3 however are only defined in CSP v2, which is currently only implemented by Chrome, Opera and Firefox. The safest method would be to use the hash digest method, option 3. Alas, when you choose option 3, you'll quickly run into the following issues:
Chrome. I'm running version 46.0.2490.80 m on a Windows PC and Chrome keeps telling me this:
Refused to execute inline script because it violates the following Content Security Policy directive: "script-src 'self' 'sha256-0ZMofb7eMqkB9IFHnGVZ6Z4chjplAavgi09shinNehs='". Either the 'unsafe-inline' keyword, a hash ('sha256-G3FpTn2EFU91Umz2fz6NyjnqeGDTr8SUdmWbsvxzfbY='), or a nonce ('nonce-...') is required to enable inline execution.
The issue? My script block contains carriage returns for readability. You know, those '\r\n' thingies which tend to differ sometimes, depending on the OS you're running. But I'm running on Windows and hosting my website locally. Yet Chrome has stripped the '\r' characters from the script before calculating the SHA256 hash to verify my script block... Ugh.
Firefox. Version 41.0.2, catching up to Chrome apparently. Loading my test site and...
Content Security Policy: The page's settings blocked the loading of a resource at self ("script-src http://localhost:21275 'sha256-0ZMofb7eMqkB9IFHnGVZ6Z4chjplAavgi09shinNehs='")
Edge. The newest browser from Microsoft, which I really want to start to use. But then I bump, as expected, into:
CSP14304: Unknown source ''sha256-0ZMofb7eMqkB9IFHnGVZ6Z4chjplAavgi09shinNehs='' for directive 'script-src' in Content-Security-Policy - source will be ignored.
Let's try Internet Explorer, version 11.0.10240.16431. I'll dump the entire console output to share this with you:
Navigation occurred.
localhost:21275
test
Amazing, no? Wait, let's try something else here. Let's remove the hash from the header, that should stop the script from running. I'll dump the console output again:
Navigation occurred.
localhost:21275
test
So don't be fooled here. Internet Explorer doesn't support CSP v2, and even v1 is only partially supported.
Let's try option 2 instead: making use of a nonce for every script block. This time, the results are looking a little bit better:
So there you have it: Content Security Policy is still not fully there yet. You can use it though, to restrict the use of other content, like webfonts, style sheets, media, ..., but for scripts our options are currently limited to either opening up 'unsafe-inline' or moving all JavaScript into files. And if you're doing ASP.NET projects, have a look at https://www.nuget.org/packages/NWebsec. This NuGet package will make implementing CSP - and other security headers - a lot easier for you :)