I upgraded my Ubuntu box and after success restart I found that WIFI was not working anymore. I knew that my wireless driver was broadcom. Verify with command

$ lspci -vnn | grep Broadcom

output:

03:00.0 Network controller \[0280\]: Broadcom Corporation BCM4312 802.11b/g LP-PHY \[14e4:4315\] (rev 01)

  1. To make it work, I first uninstalled the b43-fwcutter

     $ sudo apt-get purge b43-fwcutter

  2. Added the source deb http://ftp.de.debian.org/debian sid main contrib to /etc/apt/sources.list

  3. updated the package list by

     sudo apt-get update

  4. Then installed

     sudo apt-get install firmware-b43-lpphy-installer

    See clearly I have used the firmware-b43-lpphy-installer which is firmware for Broadcom low power physical devices

    In your case, if this doesn’t work for you then you might try to install this driver

     $ sudo apt-get install firmware-b43-installer

  5. After successfull installation, I restarted my laptop and the wifi was functional again.

Note: Also, verify that your device is not blacklisted by viewing the content of /etc/modprobe.d/blacklist.conf

if you see the line blacklist bcm43xx in the file, then just uncomment this line and save the file.

This worked for me and expect it to work for you as well. If you find any problem, please mention it in the comment and I will try to become as much helpful as possible.