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Connection to websocket not working through burp

Philippe | Last updated: Oct 17, 2022 02:28PM UTC

Hi All We have the following problem: Upon connecting to the target while proxying the traffic through burp, firefox throws an error into the dev console stating "Firefox can't establish a connection to the server at wss://target.url". Furthermore, the corresponding request to upgrade to wss from http gets answered with a 200 OK and empty body, whereas we expect a 101 Switching Protocols response. This also happens in chrome as long as the traffic goes through burp. This error does NOT get thrown, when using OWASP ZAP. With ZAP, we can see the flow of upgrading from http(s) to wss happening as it is supposed to. It needs to be noted that we needed to disable the option "Default to HTTP/2 if the server supports it" in burp to even get a connection to start. So far we have tried fiddling around with various config settings in burp that might affect this behavior (like the Settings in Proxy -> Options -> Miscellaneous), sadly with no luck so far. Is there anyone that experienced similar problems in the past and could help us out? Thanks in advance

Michelle, PortSwigger Agent | Last updated: Oct 18, 2022 08:42AM UTC

Thanks for getting in touch. In addition to the Project Options -> HTTP -> HTTP/2 setting, if you go to Proxy -> Options -> Proxy Listener -> Edit -> HTTP and disable HTTP2, do you also see the same behavior?

Philippe | Last updated: Oct 18, 2022 09:49AM UTC

Just disabled HTTP2 as per your advice. Sadly the error persists. But thanks for pointing that out, we did not think of that.

Michelle, PortSwigger Agent | Last updated: Oct 18, 2022 09:54AM UTC

Could you email some more details about what you see in Burp to support@portswigger.net? Is this a site we'd be able to access from here? If not, would you be in a position to share any packet captures with us?

Philippe | Last updated: Oct 18, 2022 11:09AM UTC

Due to NDA, we cannot share very detailed information about the site. But i'll try and setup an email with more information and an additional packet trace (if possible to redact properly).

Michelle, PortSwigger Agent | Last updated: Oct 18, 2022 12:23PM UTC