Debian consists entirely of free software. This is a reason why Broadcom LAN chips are supported by the open source drivers by default. The common issue with these drivers (brcmsmac, b43…) is that there is no WiFi devices available in network manager. To change that, the quickest possible way, we need to install non-free vendor driver on our Debian system.
Instructions below were tested on Debian 9 “Stretch”.
Important! Wired/bluetooth connection is required.
1. Add a “non-free” component to /etc/apt/sources.list for your Debian.
# Debian 9 "Stretch" deb non-free! http://httpredir.debian.org/debian/ stretch main contrib non-free
2. Install the latest linux-image, linux-headers and broadcom-sta-dkms packages. This will also install the recommended wireless-tools package. DKMS (Dynamic Kernel Module Support) will build the wl module for your system.
apt-get update apt-get install linux-image-$(uname -r|sed 's,[^-]*-[^-]*-,,') linux-headers-$(uname -r|sed 's,[^-]*-[^-]*-,,') broadcom-sta-dkms
3. Unload conflicting modules.
modprobe -r brcmsmac bcma b44 b43 b43legacy ssb
4. Load the wl module.
5. That’s it. If still there is problem, try reboot your OS.