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Error:

[Fiddler] The connection to '<the site>.com' failed. 
System.Security.SecurityException Failed to negotiate HTTPS connection with server.fiddler.network.https> HTTPS handshake to <the site>.com (for #3) failed. System.IO.IOException Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. < An existing connection was forcibly closed by the remote host

I can hit fine in web browser. I do see it is rather strong SSL (FireFox reports it as TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384, 256 bit keys, TLS 1.2)

Why isn't Fiddler able to make this connection?

Jonesome Reinstate Monica
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1 Answers1

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Seems that your client didn't try to connect via 1.2

Check: Tools > Fiddler Options > HTTPS It's set to <client>;ssl3;tls1.0

Add "tls1.2" to the protocols list

Edit: Refer to the image below for where to find the option: enter image description here

Sunny Sharma
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Neroon
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    I don't see those options in that place in fiddler. – Jonesome Reinstate Monica May 24 '17 at 01:22
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    In Fiddler 4 the option exists. look at this screenshot https://jackstromberg.com/2016/08/tutorial-using-fiddler-to-debug-saml-tokens-issued-from-adfs/fiddler-tools-telerik-fiddler-options-https-decrypt-https-traffic/ – Neroon May 24 '17 at 05:05
  • it worked me, use this screen shot. https://jackstromberg.com/2016/08/tutorial-using-fiddler-to-debug-saml-tokens-issued-from-adfs/fiddler-tools-telerik-fiddler-options-https-decrypt-https-traffic/ – Abhishek P Aug 09 '17 at 13:37
  • I suggested an edit. This error happens to me when I have ssl2 set in the same place. – Philip Rego Aug 07 '19 at 21:04
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    In `Fiddler4` it's `Tools > Options`. And the option to add a `Protocol` only becomes visible if you check `Decrypt HTTPS traffic`, after which you can click `No`, go and add the `Protocol`s needed and then uncheck the `Decrypt HTTPS traffic` option. – Aage Nov 21 '19 at 15:17
  • Thanks @Neroon I wasted 6 hrs trying to fix this issue. Your response helped me .. I was loosing my mind... Thanks again. – User M Jul 01 '22 at 17:58
  • This solution works also on below similar cases (slightly different error message). ------------------------------------------------------------------------------------------ [Fiddler] The connection to '' failed.
    System.Security.SecurityException Failed to negotiate HTTPS connection with server.fiddler.network.https> HTTPS handshake to (for #123) failed. System.ComponentModel.Win32Exception The client and server cannot communicate, because they do not possess a common algorithm     – zjg.robin Mar 02 '23 at 05:09