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Fiddler blocks all HTTPS traffic

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Yan
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Yan asked on 01 May 2019, 09:14 AM

I am using Fiddler with HTTPS decoding for development purposes (some AutoResponder rules), but recently Fiddler has started to just randomly block all HTTPS traffic at some point. That is, I am running Fiddler and everything works, and then suddenly it stops, and I get timeout on all HTTPS requests.

What I know so far:

1. Only HTTPS traffic stops, other traffic is not affected
2. Cancelling HTTPS decryption or network capture returns everything to normal (expected)
3. Restarting Fiddler helps for about a minute and then traffic stops again
4. Port 443 is not blocked, telnetting hosts on port 443 works just fine

How can I troubleshoot this issue?

Thanks in advance.

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Yan
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answered on 05 May 2019, 02:22 PM
Update with possible solution: I can tentatively say that the issue has been resolved by limiting Fiddler to 1000 sessions ("keep 1000 sessions"). While this makes sense, it's a bit strange that it can't handle much more than this—so maybe there is some other underlying issue.
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Simeon
Telerik team
answered on 06 May 2019, 08:11 AM
Hello Yan,

Thanks for the feedback. It helps us to improve the Fiddler products. I would like to ask which version of Fiddler you are using. I am also curios to know which certificate generator you are using. If it is CertEnroll, or the legacy MakeCert, could you, please, try to clear your Windows certificate store to check if this would improve the performance.

Regards,
Simeon
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Yan
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answered on 06 May 2019, 08:53 AM

Hi Simeon,

Thanks for your response.

I am using v5.0.20182.28034

Looks like my certificates were generated with CertMaker.dll, that's MakeCert, correct? I remember having the option to choose, but don't remember where that was right now.

Clearing the Windows certificate store: Indeed it helped temporarily, but it quickly went back to not working.

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Simeon
Telerik team
answered on 08 May 2019, 02:59 PM
Hi Yan,

Looks like my certificates were generated with CertMaker.dll, that's MakeCert, correct? - The CertMaker.dll is a default library which Fiddler is looking for on startup in order to load the ICertificateProvider implementation from it. The latest version of our CertMaker is using the BouncyCastle library.

I remember having the option to choose, but don't remember where that was right now. - From the menu click the Tools\Options... then click on the HTTPS tab. On the right side of the Options window you should see a "Certificates generated by [CertProviderInfo]" link. Click on it and depending on your CertMaker a Certificate Generation window with options to choose should open.

Clearing the Windows certificate store: Indeed it helped temporarily, but it quickly went back to not working. - If your CertMaker is using the MakeCert tool, I recommend installing our latest version of CertMaker and clearing your Windows certificate store.

Regards,
Simeon
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Simeon
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