MITM Proxy Cursor Debug Script

screencast-decoded.mp4

This is a POC of how to decode on the fly the aiserver requests/responses of Cursor. Take a look to the cursor-rpc Proto files extracted by @everestmz (copy included here for convenience).

How-To

The setup was done on Windows with MiTMProxy. This is to make use of the local capture feature and capture the whole Cursor APP. This cannot be run on MacOS atm, as a brew installation of MITMProxy is needed to get the local interceptor to run, which is incompatible with the PyPI version that is needed for the interception script.

Installation

Using uv

1. install uv
2. clone this repo with git clone https://github.com/LaiKash/cursor-aiserver-interceptor
3. run uv sync to create python virtual environment and install dependencies.
4. activate the environment

Using pip

Create a python virtual environment, activate it and the install the following packages with pip:

• pip install mitmproxy (don't install it with the Windows installer)

Alternative installation for protobuf

• Install protoc from the zip here: https://github.com/protocolbuffers/protobuf/releases
• The python files are already generated from the .proto file. In case you want to generate new ones (because they are incompatible with your protoc version from python): protoc.exe --python_out=. aiserver.proto

Run

• mitmweb -s mitm_cursor_proto.py --mode local
• In MitWeb, go to File > Install Certificates > Get mitmproxy-ca-cert.p12. Install the certificate as administrator (double click it and install for the whole machine).
• Close mitweb (ctrl+c it).
• mitmweb -s mitm_cursor_proto.py --mode local:Cursor (this will just intercept Cursor when you run it, feel free to use --mode local to intercept all)
• Open cursor and try some tab completion. You can use the printhelloworld.py in this repo for testing.

What to expect

You should see an attempt to parse the proto requests/responses that mitweb is receiving, in the terminal, decoded. All those requests/responses are also logged into the grpc_logs directory for future inspection. The most interesting one is the StreamCpp request, the other ones are usually not giving anything important.

If you see any warning you might want to ignore it for now.

When a "mitm session" is closed (i.e., when the mitmweb command is stopped with ctrl-C), a file with the extension .mitm is saved in the mitm_dumps directory. These files contain all the data recorded in the corresponding mitm session. To open these files, use the command: mitmweb -r mitm_dumps/[name-of-the-file].mitm.

Example video

screencast.mp4