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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?

JayC
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rpf
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  • Did you install an ISA/ForeFront server in the last two days on your local machine? Any Antivirus/Malware/Firewall software? – Alexander Galkin Dec 20 '11 at 19:00
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    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. – EricLaw Dec 22 '11 at 13:47

4 Answers4

42

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";
Imran Qadir Baksh - Baloch
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    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 – Omzig Aug 20 '18 at 13:53
  • 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 TLS1.0 and TLS1.1 were disabled, but the client was configured to use these outdated mechanisms.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. – UnhandledExcepSean Dec 10 '18 at 21:00
  • I have personally closed tls1.0 support on the server, got stuck in this for the past few hours – Emad Nov 25 '19 at 08:12
  • It seems extraordinary that Fiddler doesn't enable TLS 1.1 and 1.2 by default - lots of people must get the same problem – StuartN Mar 11 '22 at 14:35
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.

udalmik
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1

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.

Thomas Koelle
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-21

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.

rpf
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