PPTP VPN Fails Authentication But Using Correct Credentials

Question

I installed a pptp module for gnome using:

apt-get install network-manager-pptp-gnome

The VPN works in Windows 10 but i've tried this in Kali and Ubuntu and it's the same thing. The VPN i'm trying to use uses PEAP so when I add the VPN i make sure mschap and mschapv2 are selected. I have the gateway as the vpn host i'm trying to connect to. I've tried using domain\user instead of just my username and [e-mail] but neither work.

Looking in the system log it says "MS-CHAP authentication failed" but i've typed the correct credentials a million times and it works on Windows too (using pptp / peap).

Any help would be greatly appreciated!

Jan 30 22:01:06 kali NetworkManager[2457]: <info>  [1580446866.7200] vpn-connection[0x5598577d0310,309ff610-5c75-4709-a6fc-28d4ad20b86e,"XXXX",0]: Started the VPN service, PID 2576
Jan 30 22:01:06 kali NetworkManager[2457]: <info>  [1580446866.7274] vpn-connection[0x5598577d0310,309ff610-5c75-4709-a6fc-28d4ad20b86e,"XXXX",0]: Saw the service appear; activating connection
Jan 30 22:01:06 kali NetworkManager[2457]: <info>  [1580446866.8281] vpn-connection[0x5598577d0310,309ff610-5c75-4709-a6fc-28d4ad20b86e,"XXXX",0]: VPN connection: (ConnectInteractive) reply received
Jan 30 22:01:06 kali NetworkManager[2457]: <info>  [1580446866.8362] vpn-connection[0x5598577d0310,309ff610-5c75-4709-a6fc-28d4ad20b86e,"XXXX",0]: VPN plugin: state changed: starting (3)
Jan 30 22:01:06 kali pppd[2584]: Plugin /usr/lib/pppd/2.4.7/nm-pptp-pppd-plugin.so loaded.
Jan 30 22:01:06 kali NetworkManager[2584]: Plugin /usr/lib/pppd/2.4.7/nm-pptp-pppd-plugin.so loaded.
Jan 30 22:01:06 kali pppd[2584]: pppd 2.4.7 started by root, uid 0
Jan 30 22:01:06 kali NetworkManager[2457]: <info>  [1580446866.8439] manager: (ppp0): new Ppp device (/org/freedesktop/NetworkManager/Devices/3)
Jan 30 22:01:06 kali pppd[2584]: Using interface ppp0
Jan 30 22:01:06 kali NetworkManager[2584]: Using interface ppp0
Jan 30 22:01:06 kali NetworkManager[2584]: Connect: ppp0 <--> /dev/pts/1
Jan 30 22:01:06 kali pppd[2584]: Connect: ppp0 <--> /dev/pts/1
Jan 30 22:01:06 kali pptp[2589]: nm-pptp-service-2576 log[main:pptp.c:353]: The synchronous pptp option is NOT activated
Jan 30 22:01:06 kali pptp[2600]: nm-pptp-service-2576 log[ctrlp_rep:pptp_ctrl.c:259]: Sent control packet type is 1 'Start-Control-Connection-Request'
Jan 30 22:01:06 kali pptp[2600]: nm-pptp-service-2576 log[ctrlp_disp:pptp_ctrl.c:781]: Received Start Control Connection Reply
Jan 30 22:01:06 kali pptp[2600]: nm-pptp-service-2576 log[ctrlp_disp:pptp_ctrl.c:815]: Client connection established.
Jan 30 22:01:07 kali pptp[2600]: nm-pptp-service-2576 log[ctrlp_rep:pptp_ctrl.c:259]: Sent control packet type is 7 'Outgoing-Call-Request'
Jan 30 22:01:07 kali pptp[2600]: nm-pptp-service-2576 log[ctrlp_disp:pptp_ctrl.c:900]: Received Outgoing Call Reply.
Jan 30 22:01:07 kali pptp[2600]: nm-pptp-service-2576 log[ctrlp_disp:pptp_ctrl.c:939]: Outgoing call established (call ID 15460, peer's call ID 1075).
Jan 30 22:01:07 kali pppd[2584]: MS-CHAP authentication failed: E=691 Authentication failure
Jan 30 22:01:07 kali NetworkManager[2584]: MS-CHAP authentication failed: E=691 Authentication failure
Jan 30 22:01:07 kali NetworkManager[2584]: CHAP authentication failed
Jan 30 22:01:07 kali pppd[2584]: CHAP authentication failed
Jan 30 22:01:07 kali pptp[2600]: nm-pptp-service-2576 log[ctrlp_disp:pptp_ctrl.c:1005]: PPTP_SET_LINK_INFO received from peer_callid 15460
Jan 30 22:01:07 kali pptp[2600]: nm-pptp-service-2576 log[ctrlp_disp:pptp_ctrl.c:1008]:   send_accm is 00000000, recv_accm is FFFFFFFF
Jan 30 22:01:07 kali pptp[2600]: nm-pptp-service-2576 warn[ctrlp_disp:pptp_ctrl.c:1011]: Non-zero Async Control Character Maps are not supported!
Jan 30 22:01:07 kali pppd[2584]: Connection terminated.
Jan 30 22:01:07 kali NetworkManager[2584]: Connection terminated.
Jan 30 22:01:07 kali NetworkManager[2457]: <warn>  [1580446867.9275] vpn-connection[0x5598577d0310,309ff610-5c75-4709-a6fc-28d4ad20b86e,"XXXX",0]: VPN plugin: failed: connect-failed (1)
Jan 30 22:01:07 kali NetworkManager[2457]: <info>  [1580446867.9275] vpn-connection[0x5598577d0310,309ff610-5c75-4709-a6fc-28d4ad20b86e,"XXXX",0]: VPN plugin: state changed: stopping (5)
Jan 30 22:01:07 kali NetworkManager[2457]: <info>  [1580446867.9275] vpn-connection[0x5598577d0310,309ff610-5c75-4709-a6fc-28d4ad20b86e,"XXXX",0]: VPN plugin: state changed: stopped (6)
Jan 30 22:01:07 kali NetworkManager[2457]: <info>  [1580446867.9364] vpn-connection[0x5598577d0310,309ff610-5c75-4709-a6fc-28d4ad20b86e,"XXXX",0]: VPN service disappeared
Jan 30 22:01:07 kali pppd[2584]: Terminating on signal 15
Jan 30 22:01:07 kali NetworkManager[2584]: Terminating on signal 15``````

Answer 1

The pppd program used here for PPTP does not support EAP-PEAP at all. So the reason authentication fails is beause the client isn't trying EAP-PEAP/MSCHAPv2; it is actually trying direct MSCHAPv2 without any outer security layer.

You can try applying this patch for EAP-PEAP support.