Hope all are well. I got this strange problem were my Firefox browser is not sending traffic to BurpSuite. Here is what I did.
I am using AWS instance with 8GB RAM and 2 vCPU. Installed Ubuntu and BurpSuite Professional trail one month version. I am using OWASP Docker Mutillidae II image from bltsec/mutillidae-docker. I have installed Docker and started the container. The BurpSuite proxy is configured for 127.0.0.1 and port 8080, the same in punched in Firefox 127.0.0.1 and 8080. At beginning I had some problem accessing the application via localhost or 127.0.0.1/mutillidae, so I used AWS internal IP 172.31../mutillidae IP and worked. Later I did nothing tried 127.0.0.1/mutillidae and it worked.
Same instance I didn't do nothing, for past two days the traffic not flowing in Burpsuite though still the Firefox is configured to forward the traffic(there are no rules in the proxy section not to forward the traffic to proxy, it is blank). But the 127.0.0.1/mutillidae application is working directly without going through the proxy and I couldn't find the hits in the proxy, but for 172.31../mutillidae I see the hit in the proxy but site is not opening, different errors like cannot connect to 172.31 on port 80 error.
Then I disabled the firewall and Apparmor and no luck. All the above was accomplished with sudo, then some article said use non-sudo account, I created one. One of the main reason I tried non-sudo account is that BurpSuite in-built browser was not opening, but in the non-sudo account it opens. Also 172.31../mutillidae was working and I can see in the proxy(it is kind of mixed issue sometimes localhost works and other time IP works.) Before two days the local traffic was getting into the proxy and then stopped working, the IP traffic is visible on the proxy but the site doesn't opens. I deleted the Docker image and cleaned the whole image and container store, re-pulled the image and ran the container, still have issue.
To me it looks like browser is not forwarding traffic correctly. Or the BurpSuite is a weirdo like trail version is an issue. Maybe I have reinstall Firefox or maybe the Docker image is corrupted, but the access to the application works directly, it has problems with the proxy. Or using AWS instances with local proxy needs some other special configs? Please guide.