There’s a new HTTP header on the block - HTTP Public Key Pinning (HPKP). It allows the server to publish a security policy in the same vein as HTTP Strict Transport Security and Content Security Policy.
The RFC was published last month so browser support is limited, supported in Chrome 38, Firefox 35 and newer. However, there are helpful articles from Scott Helme, Tim Taubert and Robert Love on the topic and OWASP has some general info on certificate and key pinning in general. Scott has even built support for HPKP reporting into his helpful reporting service - https://report-uri.io/.
Although Chrome and Firefox will honour your public key pins, testing the header is slightly tricky as they haven't implemented reporting yet (as of Chrome 42 and Firefox 38). I spent some time trying to coax both into reporting, working under the assumption that they must have implemented the whole spec right? It seems not.
In writing this, I also wanted to note the command I used to calculate the certifcate digest that's used in the header. In contrast to other examples, this connects to a remote host to get the certificate (including allowing for SNI), outputs to a file and exits openssl when complete.
openssl s_client -connect robinminto.com:443 -servername robinminto.com |
openssl x509 -pubkey -noout | openssl pkey -pubin -outform der |
openssl dgst -sha256 -binary | base64 > certdigest.txt
I won't be using HPKP in my day job until reporting support is available and I can validate that the configuration won't break clients. There's great potential here though once the support is available.
I’ve been automating the configuration of IIS on Windows servers using PowerShell. I’ll tell anyone who’ll listen that PowerShell is awesome and combined with source control, it’s my way of avoiding snowflake servers.
To hone the process, I’ll repeatedly build a server with all of it’s configuration from a clean image (strictly speaking, a Hyper-V checkpoint) and I’m occasionally getting an error in a configuration script that has previously worked:
new-itemproperty : Filename: \\?\C:\Windows\system32\inetsrv\config\applicationHost.config
Error: Cannot write configuration file
Why is this happening? The problem is intermittent so it’s difficult to say for sure but it does seem to occur more often if the IIS Management Console is open. My theory is that if the timing is right, Management Console has a lock on the config file when PowerShell attempts to write to it and this error occurs.
I'm now blaming AppFabric components for this issue. I noticed the workflow service was accessing the IIS config file and also found this article on the IIS forums - AppFabric Services preventing programmatic management of IIS. The workflow services weren't intentionally installed and we're using the AppFabric Cache client NuGet package so I've removed the AppFabric install completely and haven't had a recurrence of the problem.
I’ve been using the ASafaWeb security analyser to scan various websites that I work on. It picks up basic configuration problems in .NET websites and, very handily, will scan periodically to make sure that misconfiguration doesn’t creep back in.
ASafaWeb was created by Troy Hunt, a software architect and Microsoft MVP for Developer Security based in Australia. Troy writes some great articles on improving application security, with a focus on .NET, and he links to those articles in ASafaWeb to illustrate why and how improvements should and can be made.
Most of the issues can be addressed in the application, generally in web.config, but the issue I’m interested in here can be solved by configuring at the server level. Here’s the output from ASafaWeb:
See that “X-Powered-By: ASP.NET” header? That one’s inherited from the IIS root configuration. We could remove it in every web.config but better to remove it once.
Troy links to his blog post on removing all of those headers – Shhh… don’t let your response headers talk too loudly. As he mentions, there are many different ways of removing those headers – he goes into IIS Manager UI and removes it from there.
I’m trying to make sure that I script server configuration changes. This is a great way of documenting changes and allows new servers to be configured simply. I want servers that can rise like a phoenix from the metaphorical ashes of a new virtual machine rather than having fragile snowflake that is impossible to reproduce (thanks to Martin Fowler and his ThoughtWorks colleagues for the imagery).
So, the script to remove the “X-Powered-By” header turns out to be very straightforward once you figure out the correct incantations. This assumes you have Powershell and the Web Server (IIS) Administration Cmdlets installed.
That’s a lot of words for a very little configuration change but I wanted to talk about ASafaWeb and those ThoughtWorks concepts of server configuration. I also need to mention my mate Dylan Beattie who helped me out without knowing it. How? StackOverflow of course.