Questions on Fiddler Forum

10 answers

2.1K+ views

Hi,

I'm trying to setup fiddlercore to accept remote connections on port 80 and 443 then act as a proxy to incoming connections - without being configured as the system proxy on the client machine. Similar to how Squid can be configured in transparent mode. So far I've tried a number of variations on the below with no luck.

FiddlerApplication.Startup(3145, false, false);
var altEndPoint = FiddlerApplication.CreateProxyEndpoint(80, true, "*");
altEndPoint.Attach();
var oSecureEndpoint = FiddlerApplication.CreateProxyEndpoint(443, true, "*");
oSecureEndpoint.Attach();

Is what I'm trying to do doing possible, would really appreciate any pointers!

Extensions and Customization

answered on 23 Feb 2018

2 answers

278 views

Fiddler v5 does not run as 64bit

I've started hitting a lot of Out Of Memory issues in Fiddler over the last few months. After seeing this, I realized that my problems coincided with upgrading to the latest version (v5) when Fiddler started being a 32-bit only application. It would be really nice if we could get a new 64-bit compatible release of Fiddler.

As a temporary workaround, I've set the 'number of sessions to keep' option really low and that has helped but that starts impacting the usability of the tool and still doesn't solve it completely.

Windows

answered on 20 Feb 2018

1 answer

7.7K+ views

Capture localhost websocket traffic

Hi,

is it possible to capture localhost (client and server on the same box) websockets communication? I tried using what you suggested to capture local http/https traffic but it is not applicable to websockets.

Thanks,

Eli

Windows

answered on 20 Feb 2018

1 answer

382 views

FidllerCore license & features

Hello Telerik team,

I've downloaded a free version of FiddlerCore and run demo project just to try it. This is really cool API!

So, I plan to use it in a .net project for automation testing but I would like to clarify a couple of questions before using it:

Are there any limitations on a free license of FiddlerCore for using it in the automation testing project? Could automation testing project mean like an internal business application? My project is a .net project (c#) which is not distributable within my company, it is not used as a commercial product and it is not distributed to our end customers. It is used only in CI/CD pipeline but it is not an educational project.
Is there any difference in the functionality of FiddlerCore free and commercial licenses? Are there any limitations on the features of FiddlerCore free license?
As far as I understand a commercial license is per application for 1 year but on all products page, it says that license is per developer. Please confirm the correct one option.

Thank you and best regards,

Dmytro

FiddlerCore

answered on 20 Feb 2018

7 answers

477 views

Filter Issues

Hi,

I have been using Fiddler for several years now and one thing has consistently bothered me. Whenever I add a filter, say, "Show only processid X", it will filter out everything else. So far so good. However, if something new comes in (usually visual-studio related) that wasn't on-screen prior to the filter it isn't filtered.

Here are some reproduction steps to see what I mean:

* Open Fiddler.

* Use Composer to write up a post against a local dev API endpoint.

* Wait for other items to show up (via browser, VS, etc.)

* Right-Click the Fiddler post and choose "Show only Process = x"

* Watch everything but that process filter out.

* Wait a few moments.

* In my dev environment, new things keep cropping up.

I have included a screenshot showing that a filter is active, with a new instance of svchost showing up after the filter was applied. Is there some way that I can tell Fiddler to apply my filter to any future traffic in this session and not just previous traffic?

Fiddler Classic

answered on 20 Feb 2018

1 answer

138 views

FiddlerCore - SSL Prompt every program launch

hey telerik,

I have been using fiddler core for a while now and the problem I've been having (which only recently started happening) is that when I try to capture/decrypt SSL with 'CertMaker.TrustRootCert();' it prompts me each time to install the certificate. I have used this code before and this has never happened.

This is my startup code if you need it >

CertMaker.trustRootCert();
FiddlerApplication.Startup(8877,FiddlerCoreStartupFlags.Default);
oSecureEndpoint = FiddlerApplication.CreateProxyEndpoint(iSecureEndpointPort, true, sSecureEndpointHostname);
FiddlerApplication.BeforeRequest += encodeOnReq;

thanks, xev

FiddlerCore

answered on 20 Feb 2018

1 answer

406 views

HTTPS traffic not captured using FiddlerCore on Linux

01.

public class ProxyConfig

02. {

03. private const string SecureEndpointHostname = "localhost";

04. private readonly int _secureEndpointPort = 18888;

05.

06. private static readonly ICollection<Session> AllSessions = new List<Session>();

07.

08. private static Fiddler.Proxy _secureEndpoint;

09.

10. private static readonly LoggerCnx Logger = new LoggerCnx();

11.

12. public void SetupProxyListener()

13. {

14. // This is a workaround for known issue in .NET Core - https://github.com/dotnet/coreclr/issues/12668

15. CultureInfo.DefaultThreadCurrentUICulture = new CultureInfo("en-US");

16.

17. FiddlerApplication.BeforeRequest += session =>

18. {

19. // In order to enable response tampering, buffering mode MUST

20. // be enabled; this allows FiddlerCore to permit modification of

21. // the response in the BeforeResponse handler rather than streaming

22. // the response to the client as the response comes in.

23. session.bBufferResponse = false;

24. lock (AllSessions)

25. {

26. AllSessions.Add(session);

27. }

28. };

29.

30. Logger.Info($"Starting {FiddlerApplication.GetVersionString()}...");

31. CONFIG.IgnoreServerCertErrors = true;

32. CONFIG.bCaptureCONNECT = true;

33.

34. FiddlerApplication.Prefs.SetBoolPref("fiddler.network.streaming.abortifclientaborts", true);

35.

36. FiddlerCoreStartupFlags startupFlags = FiddlerCoreStartupFlags.Default;

37. startupFlags = (startupFlags | FiddlerCoreStartupFlags.DecryptSSL);

38.

39. FiddlerApplication.Startup(BaseConfiguration.ProxyPort, startupFlags);

40.

41. Logger.Info("Created endpoint listening on port {0}", BaseConfiguration.ProxyPort);

42.

43. Logger.Info("Starting with settings: [{0}]", startupFlags);

44. Logger.Info("Gateway: {0}", CONFIG.UpstreamGateway.ToString());

45.

46. // Create a HTTPS listener, useful for when FiddlerCore is masquerading as a HTTPS server

47. // instead of acting as a normal CERN-style proxy server.

48. _secureEndpoint = FiddlerApplication.CreateProxyEndpoint(_secureEndpointPort, true, SecureEndpointHostname);

49. if (null != _secureEndpoint)

50. {

51. Logger.Info("Created secure endpoint listening on port {0}, using a HTTPS certificate for '{1}'", _secureEndpointPort, SecureEndpointHostname);

52. }

53. }

54.}

Trying to capture all traffic from browser using FiddlerCore using the .NetStandard libraries. Above is what I have.

Everything seems to work fine on Windows, all traffic is captured, HTTP and HTTPS. The problem arises when I'm trying to do the same when running the code on Linux (tried it on both VM and Linux conainer, Ubuntu 16.04). Any idea what I'm I'm missing?

Linux

answered on 19 Feb 2018

3 answers

418 views

Customize rules window not opening - xdg-open: unexpected argument

Fiddler working well except I cannot create customize rules (want to implement force CORS response)

When selecting Customize Rules from the menu nothing appears to happen.

Checking the console i can see the following error:

xdg-open: unexpected argument '/home/patrick/Fiddler2/Scripts/CustomRules.cs'
Try 'xdg-open --help' for more information.

This message tells me fiddler is looking for the CustomRules.cs in the wrong location (basically under my HOME directory). Fiddler is installed in /home/tools/fiddler not my HOME directory.

Have I missed setting some environment variable (FIDDLER_HOME) or something.

Thanks in advance.

Linux

answered on 18 Feb 2018

0 answers

313 views

Fiddler Silent Install

I am trying to do a silent package for Fiddler 5 , latest version and I am using
FiddlerSetup.exe /S to do the silent install , it installs but it installs in c:\user folder and I want it to install in c:\programfiles folder , Is there a way to get .msi file instead of .exe ? I did not had any issues in previous version of fiddler. Please let me know any suggestions ?

Windows

asked on 14 Feb 2018

1 answer

579 views

Fiddler 'fixes' client certificate prompt - why?

Hi everyone...

I'm posting here partly out of desperation and partly because I've hit the upper limit of my knowledge and need to understand the issue I'm facing.

I have several users at my company who are based in Luxembourg and access a banking application that authenticates them via client certificates loaded from a smart card. A couple of weeks ago, Internet Explorer stopped prompting them for their client certificate when they navigate to the login page for the application.

Users at our London office who use the same application are not seeing this issue.

After a couple of days of troubleshooting using various methods I installed Fiddler to attempt to gain some insight into the https transaction/ssl handshake to try and see where the problem is.

Prior to this, using Wireshark to analyse the transaction I can tell that the Certificate Request is making it through to the workstation, along with the list of CAs trusted by the server. The client certificate is valid and present, as is the Root CA and Intermediate CA that issued the client Cert.

However, Internet Explorer 11 refuses to prompt the user to select the valid certificate and therefore they are unable to access the application.

Where it gets interesting is that as soon as I run Fiddler and fire up the login page again, it behaves exactly as I would expect, and the client certificate prompt appears. Note that this behaviour is exhibited without a client certificate specified in Fiddler and with HTTPS decryption turned off. I feel like if I can get to the bottom of why exactly this works, I might be able to solve the main issue - but I'm at a dead end.

I would greatly appreciate any advice on what to look for next. When Fiddler is proxying the traffic, the issue goes away and IE prompts for the client cert. As soon as I turn it off, it stops again.

I have read nearly every post online I can find about client certificate prompts, etc, including many written by Eric. However I just cannot seem to get to the bottom of why it's not happening.

Many thanks in advance.

Windows

answered on 13 Feb 2018