Greynoise helps security teams focus on potential threats by reducing the noise from logs, alerts, and SIEMs. They constantly watch for badly behaving internet hosts, keep track of the benign ones, and use this research to classify IP addresses. Teams can use these classifications to only focus on things that (potentially) matter.

They also have a generous (10K calls/day), free community API which does not require credentialed access and returns a subset of information that the full API does. This is handy for folks who can’t afford the service or who only need to occasionally poke at IP addresses.

Andrew, GN’s CEO, tweeted out a super-hacky shell one-liner, the other day, that grabs the external IPs of all the ESTABLISHED IPv4 TCP connections and runs them through the community API via curl. Even though I made it a bit less-hacky:

sudo netstat -anp TCP \
  | rg ESTAB \
  | rg "(?:(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)\.){3}(?:25[0-5]|2[0-4][0-9]|[01]?[0-9][0-9]?)" -o \
  | rg -v "(^127\.)|(^10\.)|(^172\.1[6-9]\.)|(^172\.2[0-9]\.)|(^172\.3[0-1]\.)|(^192\.168\.)" \
  | rg -v "$(dig +short viz.greynoise.io @9.9.9.9 | rg '^\d' | tr '\n' '|' | sed -e 's/.$//g')" \
  | sort -u \
  | while read IP; do echo $(curl --silent https://api.greynoise.io/v3/community/$IP); done |
  Rscript -e 'tibble::as_tibble(jsonlite::stream_in(file("stdin"), verbose=FALSE))'

its still a “run-on-demand” process that you could put in a script and launchd, but then you’d still have to keep a terminal up or remember to watch some file. Plus, it relies on full executables.

I decided to make things a bit easier for folks on macOS Big Sur by cranking out a small SwiftUI app I’ve dubbed GreyWatch:

Each list entry show an IP address your Mac previously connected to (since app launch) or currently has established TCP connections to. The three indicator dots show (in order) whether Greynoise has detected scanning behavior from the IP address within the last 30 days, whether it has a “Rule It OuT” (RIOT) classification, and what — if any — classification the IP address has. The app only shows an IP address once even it you continue to connect to it and it puts new connections on top.

If an IP address has a classification, double-clicking it will open your default browser to the Greynoise visualizer, otherwise said double-click will take you to the IPInfo entry for the IP address.

Needless to say, if your Mac is talking to a host Greynoise has classified as horribad, your other 99 problems no longer take precedence. I’ll likely add a notification action if that condition occurrs.

There’s an “Export…” item in the file menu that lets you save a copy of the current IP list (with metadata) to an ndlines formatted JSON file.

The app does not shell out to dig or netstat and has a light memory and energy footprint.

There are pre-built, notarized binaries in the releases section, and I’ll gradually be adding features (submit yours via new issues!). You can also submit bug reports or other questions via GH issues as well.

Many thanks to Andrew and team for their generous free tier, which enables semi-useful community hacks like this one!