Re: FireFox re-using HTTP2 connection to a wrong IP address & MITM attacks.

On Thu, 9 Jun 2016, [email protected] wrote:

>
> host_1.domain.com resolves to  IP_ADDR_1 (v4) and IP_ADDR_2 (v6)
>
> host_2.domain.com resolves to IP_ADDR_1 (v4).
>
> both servers support SPDY/ HTTP2 and share the sam wildcard SSL certificate for *.domain.com

> User opening secure HTTPS connection to https://host_1.domain.com and FF 
> successfully opening a page, connecting to IP_ADDR_2 (because IPv6 usually 
> preferred over IPv4 connections).
>
> After that user trying to open URL https://host_2.domain.com, but FireFox 
> will NOT connect to IP_ADDR_1 !!!! Instead, FireFox is going to reuse it's 
> existing connection to IP_ADDR_2 (despite the fact it does NOT belong to 
> host_2.domain.com).

As you know, but not everybody reading this email might be up to speed with, 
Firefox does this to keep the number of TCP connections to a minimum when it 
speaks HTTP/2. "unsharding" as we sometimes call it! =)

They both have a cert that covers both hosts and they both share at least one 
IP address. And they speak HTTP/2, so in the rare occasion that this would be 
a wrong assumption the server can return 421.

> Patrick claims that the fact that both domains are sharing "IP_ADDR_1", it 
> is also "Ok" to assume that all the rest of IP addresses of host_1 can be 
> used to send requests to host_2.

Not only beause of the IP address overlap. The cert also suggests this.

> To me it sounds like a complete nonsense and such behaviour most likely will 
> lead to MITM vulnerability.

I don't see how a malicious player can MITM this (in any ways not already 
existing). Your scenario in the bug was a bit overboard and involved you 
installing a malicous party's CA cert in your browser, and if you do that you 
will certainly be a victim of MITM even easier than using this approach. Can 
you explain a MITM scenario without you shooting yourself in the foot first?

-- 

  / daniel.haxx.se