"I updated from windows 10 to windows 11...Fiddler Everywhere was working last week when I was using on Windows 10. After upgrading, I tried to use it again today and cannot establish a remote connection to monitor traffic from a mobile device. I noticed when I first opened Fiddler I received a windows firewall notification. The option to "allow" was greyed out and I could only close the prompt. I am assuming the problem with connecting is related to the firewall but these seem to be managed by the organization. Please help allow traffic through Fiddler to assist in my debugging workflows."
I don't use Fiddler, and my team doesn't have internal documentation on troubleshooting Fiddler. I enclosed some screen captures of what the user has sent us. He is an Administrator on his Windows laptop, but I noticed some duplicate entries in his Windows Firewall that are grayed out, likely to Group Policy.
Any assistance would be greatly appreciated.
1 Answer, 1 is accepted
Hello Saul,
As you have noted, an administrative policy within the firewall settings restricts the use of applications like Fiddler within the company environment.
There is no need to troubleshoot Fiddler, as the issue is unrelated to the Fiddler application. Instead, the user should use elevated privileges (or contact his company administrators) to have full access to the Windows Firewall and settings, allowing him to control the checkboxes currently greyed out. While he might have some administrative privileges, his company administrators seem to limit his account, so he probably needs to contact them, as there is not much he can do with limited access. Ultimately, his system administrators should allow the Fiddler application access to the public and private networks. The Fiddler application should also be able to set/unset the system proxy and install and trust its own CA certificate.
As a side note, the user could try completely uninstalling Fiddler Everywhere and then reinstalling it using the per-machine installation option (refer to the screenshot). This option will specifically require administrative rights to proceed, which can help the user determine whether his administrative accounts are sufficient to grant Fiddler access to public networks. If that does not resolve the issue, he will need to contact his company's administrators.
Regards,
Nick Iliev
Progress Telerik
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Thank you for the reply. I will have the user try to uninstall and re-install Fiddler Everywhere first. But now my concern is why Fiddler components are listed twice--and if the rules are conflicting with each other. FYI, I initially routed this to the company-wide Network team, but it was returned back to me, as they insisted the issue was solely on the user's system (but did not resolve it).
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"I uninstalled Fiddler and reinstalled and it still does not work. I noticed that it kept my existing rules and sessions so it seems like it didnt wipe my user folders. In Windows Defender I still have duplicate entries for Fiddler as well. I know im on VPN but I noticed my home network is Public, but it wont let me switch to Private. I was thinking this could be a cause as the firewall settings are configured to allow Domain and Private. Certainly not an expert and dont know how the VPN plays in to this but thought I would mention."
Fiddler does not set or unset rules in the OS firewall - all rules are set by the OS firewall and through explicit policies. Additionally, multiple firewall entries for the same process can exist for various reasons, such as regulations for incoming and outgoing traffic, rules for different ports, rules for different users, and other factors (see some listed here). Therefore, having multiple rules for Fiddler should not be an issue—unless the administrator or the current user explicitly modifies them so that they limit the access. The user can also delete all firewall rules related to Fiddler if needed, allowing the firewall to set them automatically on the first application start. Note that the current user should have administrative rights during the initial start of Fiddler to successfully set the firewall rules. One thing the user can try is to start Fiddler as an administrator.
It's worth noting that Fiddler does not work automatically with most VPN tools, and explicit configuration is required when such tools are used (for example, using Fiddler alongside CiscoVON here). However, that is unrelated to the firewall issue experienced.
If the user wants to completely uninstall Fiddler and remove all previously set app configurations then they must explicitly delete the Fiddler-generated folders in the application path, as noted in the following article:
It is important to note that deleting the above folder will also delete all locally saved snapshots, so this action should be taken with caution (and a backup should be created if needed).
Finally, the user can also provide us with the Fiddler application log files, which may contain information related to the issue experienced. These files are accessible through the Help > Open Applications Log Folder option. Note that these files may contain sensitive information, so we recommend sharing them via a private ticket rather than through the public forum.
As a side note, the Fiddler Everywhere application might prompt for access to a public network during the initial sign-in attempt.
If that is the case, the user can safely ignore the Windows security prompt and proceed with the login (which internally will use the localhost address and not a public or private IP). Once he gets back to the Fiddler app, he can continue his work.