Sorry to "hijack" your post but I was going to start a new thread similar to this- my X1 Carbon Gen 4 has the AC 8260. Earlier this year (February or so) I'm almost 100% positive that packet injection was working as I was able to capture WPA handshakes from targets. I ended up removing Kali from my dual boot setup. About a week ago I reinstalled Kali 2017.2 in dual boot config, loaded correct repositories, ran apt-get clean && apt-get update && apt-get upgrade -y && apt-get dist-upgrade -y and went on my way. A neighbor of mine allows me to use his network for pentesting so I focused airodump-ng on his ssid. I receive a handshake, but it's from my own network.... I verified this by running everything as normal, turning off wifi on my phone and reconnecting. I ran airmon-ng check kill, airmon-ng start wlan0 and then airmon-ng -9 wlan0mon. I'm not on my laptop but the output stated packet injection was not working. Previously, I did not have to add any drivers to get this card to work. As I said, earlier this year I'm 100% sure it was working. I'm not sure if something changed with the new Kali rolling version or what. I went ahead and ordered an Alfa AWUS036NHA with the 9db antenna just in case. I tried loading the proprietary firmware drivers (not positive they were the right ones) and still nothing. Not sure why packet injection would have worked earlier this year and not now, but I'm still very new to linux/kali/pentesting. Any help would be appreciated!