Fiddler Check for Updates fails with 502

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Fiddler Classic
Gavin
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Gavin asked on 23 Dec 2022, 01:51 AM

I'm using Fiddler Classic v5.0.20211.51073 for .NET 4.6.1 Built: Wednesday, 15 December 2021 on Windows 11.

The update check at start-up, or if manually performed, always fails (see attachment).

The captured traffic is shown below.

What's causing the issue and how do I rectify it?

Thanks.

 

GET https://www.fiddler2.com/UpdateCheck.aspx?isBeta=False HTTP/1.1
User-Agent: Fiddler/5.0.20211.51073 (.NET 4.8; WinNT 10.0.22621.0; en-AU; 8xAMD64; Auto Update; Full Instance; Extensions: APITesting, AutoSaveExt, EventLog, FiddlerOrchestraAddon, HostsFile, RulesTab2, SAZClipboardFactory, SimpleFilter, Timeline)
Pragma: no-cache
Host: www.fiddler2.com
Accept-Language: en-AU
Referer: http://fiddler2.com/client/5.0.20211.51073
Accept-Encoding: gzip, deflate
Connection: close


HTTP/1.1 502 Fiddler - Connection Failed
Date: Fri, 23 Dec 2022 01:22:54 GMT
Content-Type: text/html; charset=UTF-8
Connection: close
Cache-Control: no-cache, must-revalidate
Timestamp: 11:22:54.613

[Fiddler] The connection to 'www.fiddler2.com' failed.  <br />System.Security.SecurityException Failed to negotiate HTTPS connection with server.fiddler.network.https&gt; HTTPS handshake to www.fiddler2.com (for #1) failed. System.IO.IOException Unable to read data from the transport connection: An existing connection was forcibly closed by the remote host. &lt; An existing connection was forcibly closed by the remote host

                                                                                    

 

 

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Nick Iliev
Telerik team
answered on 23 Dec 2022, 07:37 AM

Hi Gavin,

 

The update endpoint utilizes TLS 1.2, and when Fiddler Classic is not explicitly instructed to use that protocol version, the handshake fails, which leads to the error you are seeing.

To enable TLS1.2 in Fiddler Classic, go to Tools > Options > HTTPS and click on the Protocols field. Then add the wanted protocol versions as follows:

<client>;ssl3;tls1.0;tls1.1;tls1.2

 

Regards,
Nick Iliev
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Gavin
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commented on 23 Dec 2022, 08:26 AM

Thanks Nick. That worked.
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Nick Iliev
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