Re: Git via MITM transparent proxy with HTTPS Interception

On 2021-04-13 at 12:07:58, Vitaly VS wrote:

Yes, with some important caveats. The proxy must be completely transparent. It must not modify or impede the data in any way, it must speak both HTTP 1.1 and HTTP 2 correctly and fully, and the proxy must speak TLS completely correctly, including terminating the connection in accordance with the protocol. It must be completely impossible to tell that a proxy is being used.

I do want to point out that TLS interception is by definition a security vulnerability and almost always significantly weakens security, often by using weaker protocols, breaking or disabling certificate verification, and impeding the upgrading and interoperability of the protocol[0]. You should definitely read and understand the literature about TLS intercepting proxies and have personally verified that your implementation is free of vulnerabilities before deploying. You shouldn't rely on your implementer for this information, because they usually aren't aware that their implementation has vulnerabilities.

Also, my experience is that many, many proxies of this nature are completely broken and don't work correctly, so if you are not fully aware of what's going on and haven't fully tested your implementation, you shouldn't deploy this technology. I frequently answer questions from users in scenarios such as this who are having problems due to a broken proxy and often have to tell them to contact their network administrator. I therefore do not in any sense recommend deploying such infrastructure.

Git really does need a properly functioning HTTP and TLS implementation and things tend to break in a variety of ways when encountering broken proxies. I would say "exciting ways", but I recognize them all now and they're not exciting anymore.

Your proxy is broken and doesn't speak the protocol correctly. It isn't a transparent proxy. You should either remove it or contact your network administrator to have it removed.

[0] https://www.ftc.gov/system/files/documents/public_comments/2016/09/00019-129028.pdf