zarp VS mitmproxy

Zarp - Network attack tool centered around the exploitation of local networks.

Mainly this was just myself getting irritated at MS Teams and trying to figure out what it was doing. It was a couple years ago and my current company doesn't use teams, thankfully, so I can't really see if its still valid.

From what I remember..

There are files on the disk that get updated/overwritten with pulls from the server every time it launches. Somewhere in AppData I think. A few of these are config files (with lots of interesting looking settings, including beta features).

One of the config entries specifies a telemetry endpoint (which, you _could_ figure out with a network tracing tool but there are a ton of MS telemetry endpoints your machine is probably talking to. Best to just grab the one explicitly being used from the config like this). I forget the full name of the setting but the name pretty clearly indicates its for telemetry, and the file is clearly a config file. If you can't find it just by browsing the structure, try a multi-file search tool and look for 'telemetry' or URL/hostnames.

You can't really change the value on disk and make it just take effect from there, since it gets downloaded from the server and overwritten before Teams loads. There might be some tricks you can do locally to persist the change but nothing seemed to work for me. You could override response from server via mitmproxy but that requires finding where it comes across the wire at launch time and then building a script/config to replace it.

Anyway, you can block that telemetry endpoint from a firewall and see your memory bloat. Or you can intercept that endpoint in any mitm proxy. I went with this [mitmproxy](https://mitmproxy.org/). From there you can capture the content it sends to the endpoint, or even change the response the server sends (Teams just seems to expect a 200 code back).

The telemetry data itself is some kind of streaming event format. I think I even found documentation on the structure on some microsoft website, so its likely a reused format.

It's pretty straightforward.

I couldn't spend too much time on it and now it's not something I even use, but some cool things you might want to try if you dive deeper into this:

- Overwrite the config file as it returns from the server, to turn on EU data protection, change various functionality you're not supposed to, or flip some feature flags.

- Figure out if there's a feature flag or even other overwrite to fully disable the metrics so they aren't even collected, from anywhere in the app.

- Intercept telemetry, return an 'OK' response and drop the data from telemetry, or maybe document what they collect more definitively if you think there's interest somewhere. This keeps your privacy but doesn't really do anything for performance.

- Interfere with the data before actually returning it, maybe try playing with event contents and channel/user indicators. Microsoft probably won't like this if they notice, but it's unlikely they'll even notice.

This statement gives a false sense of security. You can use a transparent proxy, like mitmproxy, to view HTTPS traffic - https://mitmproxy.org/. https://reedmideke.github.io/networking/2021/01/04/mitmproxy-openwrt.html

You'll need to install mitmproxy and set it up on your computer and iOS. I won't go into too much detail here on how to do this, but there are plenty of guides available. This is a pretty good one: https://nadav.ca/2021/02/26/inspecting-an-iphone-s-https-traffic/

TIL this goes back to 2006, how cool! We nowadays have a much simpler version as a mitmproxy example: https://github.com/mitmproxy/mitmproxy/blob/main/examples/ad.... Although it obviously does not work as well anymore with everything being HTTPS nowadays (unless you trust the cert of course). :)

Perhaps you could have your device use a proxy that can do the HTTPS unwrap for you? https://mitmproxy.org/ maybe?

A great way to test the effectiveness of a pinning implementation is by simulating an MITM attack. Tools like Mitmproxy or Wireshack allow us to create a test environment to monitor, intercept, and proxy network requests for a test host.