Fiddler: Error 502 Proxy Error

Question

I am using Fiddler to debug all HTTP request of my ASP.NET application.

For a while (about 6 months) I had no problem. All HTTP requests appeared on Fiddler and so on.

The last two days Fiddler stoped working :/ Always returns the same error: "The request failed with HTTP status 502: Proxy Error ( The ISA Server denied the specified Uniform Resource Locator (URL). )."

The strange thing is that only happens to my application, i. e. all HTTP requests from youtube, email, etc, appear on Fiddler.

What is the problem here?

Cirilla

Did you install an ISA/ForeFront server in the last two days on your local machine? Any Antivirus/Malware/Firewall software? – Hewie

Microsoft's corporate network hits this; it occurs when the proxy server denies bounce-back to prevent IPSEC circumvention. Without Fiddler running, change IE's proxy settings to "Automatically detect settings" then restart Fiddler. – Korn

Answer 1

I solved my problem =)

I seems that something changed at my company network. So I changed the file CustomRules.js from Fiddler and added some lines at OnBeforeRequest.

Now, everything works just fine

Best regards.

Cirilla

Wich lines? I have the same problem here! – Nomadic

Please mention what changes you did to solve the problem. This doesn't helps me at all. – Mylo

Answer 2

From my case adding this line on OnBeforeRequest function in Fiddler Script fixed it for me,

oSession["x-OverrideSslProtocols"] = " ssl3;tls1.0;tls1.1;tls1.2";

Heptamerous

tls was my problem, had to go to "Fiddler | Tools | Options... | HTTPS | Click link to change Protocols to include tls 1.1 and 1.2 – Dunkin

We've encountered this issue when upgrading to new servers. TLS1.0 and TLS1.1 were disabled, but the client was configured to use these outdated mechanisms. Simple work around was to enable TLS1.0 and 1.1 on the server for the time being. – Frazzle

I have personally closed tls1.0 support on the server, got stuck in this for the past few hours – Kerrison

It seems extraordinary that Fiddler doesn't enable TLS 1.1 and 1.2 by default - lots of people must get the same problem – Satrap

Answer 3

I had the same issue with Fiddler - my HTTPS site worked fine in IE, however got 502 error in Chrome. After analyzing the issue, I found that has manual proxy enabled in Fiddler (not recommended):

Tools -> Fiddler Options -> Gateaway

it was the root cause of this strange behavior. Switching to "System Proxy" made this working for both IE and Chrome.

Sabin

HI, Tools where ? in fiddler ? – Deandra

Answer 4

I had a scenario where production url was https and test was http.

When wrongly calling test with https in fiddler then I got 502 and ended here on stack overflow.

I will just leave this here in case anyone else does the same mistake.

Bushing