What is point of SSL if fiddler 2 can decrypt all calls over HTTPS?

53
votes

I asked a question here a while back on how to hide my http request calls and make them more secure in my application. I did not want people to use fiddler 2 to see the call and set up an auto responder. Everyone told me to go SSL and calls will be hidden and information kept safe.

I bought and installed an SSL Certificate and got everything set up. I booted up fiddler 2 and ran a test application that connect to an https web service as well as connected to an https php script.

Fiddler 2 was able to not only detect both requests, but decrypt them as well! I was able to see all information going back and fourth, which brings me to my question.

What is the point of having SSL if it made zero difference to security. With or without SSL I can see all information going back and fourth and STILL set up an auto responder.

Is there something in .NET I am missing to better hide my calls going over SSL?

EDIT

I am adding a new part to this question due to some of the responses I have received. What if an app connects to a web service to login. The app sends the web service a username and a password. The web service then sends data back to the app saying good login data or bad. Even if going over SSL the person using fiddler 2 could just set up an auto responder and the application is then "cracked". I understand how it could be useful to see the data in debugging, but my question is what exactly should one do to make sure the SSL is connecting to the one it was requesting. Basically saying there cannot be a middle man.

3
c#ssl.net-4.0fiddlerencryption
i do believe it can only decrypt the info intended for you machine because you already have the private key – Mark
That is correct -- it's similar to any other web debugging proxy-- as is mentioned in Alexei's answer below, such proxies only inspect information intended for your machine, thus assisting in debugging (hence the name 'debugging proxy') but not allowing one to arbitrarily decrypt calls made from other machines. Thus, SSL is still secure, but observable locally, so that one can debug more efficiently. – waxspin
Your modification of the question puts a totally different question, than the original one. You need to validate the certificate sent by the server properly. The way to do this depends on how you connect (what classes are used etc). – Eugene Mayevski 'Callback

3 Answers

53
votes

This is covered here: http://www.fiddlerbook.com/fiddler/help/httpsdecryption.asp

Fiddler2 relies on a "man-in-the-middle" approach to HTTPS interception. To your web browser, Fiddler2 claims to be the secure web server, and to the web server, Fiddler2 mimics the web browser. In order to pretend to be the web server, Fiddler2 dynamically generates a HTTPS certificate.

Essentially, you manually trust whatever certificate Fiddler provides, the same will be true if you manually accept certificate from random person that does not match domain name.

EDIT: There are ways to prevent Fiddler/man-in-the-middle attack - i.e. in custom application, using SSL, one can require particular certificates to be used for communication. In case of browsers, they have UI to notify user of certificate mismatch, but eventually allow such communication.

As a publicly available sample for explicit certificates, you can try to use Azure services (i.e. with PowerShell tools for Azure) and sniff traffic with Fiddler. It fails due to explicit cert requirement.

9
votes

You could set up your web-service to require a Client-side certification for SSL authentication, as well as the server side. This way Fiddler wouldn't be able to connect to your service. Only your application, which has the required certificate would be able to connect.

Of course, then you have the problem of how to protect the certificate within the app, but you've got that problem now with your username & password, anyway. Someone who really wants to crack your app could have a go with Reflector, or even do a memory search for the private key associated with the client-side cert.

There's no real way to make this 100% bullet proof. It's the same problem the movie industry has with securing DVD content. If you've got software capable of decrypting the DVD and playing back the content, then someone can do a memory dump while that software is in action and find the decryption key.

6
votes

The point of SSL/TLS in general is so that the occasional eavesdropper with Wireshark isn't able to see your payloads. Fiddler/Burp means that you interacted with the system. Yes, it is a very simple interaction, but it does require (one) of the systems to be compromised.

If you want to enhance the security by rendering these MITM programs useless at such a basic level, you would require client certificate authentication (2-way SSL) and pin both the server and client certificates (e.g. require that only the particular certificate is valid for the comms). You would also encrypt the payloads transferred on the wire with the public keys of each party, and ensure that the private keys only reside on the systems they belong to. This way even if one party (Bob) is compromised the attacker can only see what is sent to Bob, and not what Bob sent to Alice. You would then take the encrypted payloads and sign the data with a verifiable certificate to ensure the data has not been tampered with (there is a lot of debate on whether to encrypt first or sign first, btw). On top of that, you can hash the signature using several passes of something like sha2 to ensure the signature is 'as-sent' (although this is largely an obscure step).

This would get you about as far in the security way as achievable reasonably when you do not control (one) of the communicating systems.

As others mentioned, if an attacker controls the system, they control the RAM and can modify all method calls in memory.