Loop webpage

[herson]

There are some sites like this https://vk.com/ that just because fiddler is open makes the site loop the capcha challenge and not stop doing it. How to resolve this? Thanks.

[Nick Iliev]

Hello Herson,

 

Many servers, especially those employing anti-bot mechanisms like CAPTCHAs, utilize additional security measures such as TLS fingerprinting. This approach ensures that they are communicating with the intended client application and not with a middle-man, as Fiddler does when acting as a man-in-the-middle proxy. While we cannot determine the exact reason why the CAPTCHA on the specified site is not functioning—since the page is blocked within our network due to privacy concerns—it is very likely that the VK server is unable to complete the TLS handshake during the CAPTCHA verification for similar reasons.

Another possibility is that the server requires a newer version of HTTP (like HTTP/2) or TLS (like TLS 1.3), which are unsupported in FIddler Classic. If that is the case, then you could try capturing the page while using Fiddler Everywhere with HTTP/2 support enabled (through the Settings > Connections> Enable HTTP/2 support option).

 

Regards,
Nick Iliev
Progress Telerik