google_auth_pam with static-challenge not working

[dkudos]

Hello All!

I am running Centos 7 with Openvpn:
OpenVPN 2.4.6 x86_64-redhat-linux-gnu [Fedora EPEL patched] [SSL (OpenSSL)] [LZO] [LZ4] [EPOLL] [PKCS11] [MH/PKTINFO] [AEAD] built on Apr 26 2018

I have configured /etc/pam.d/openvpn:
auth [success=1 default=ignore] pam_unix.so nullok_secure
auth required /lib64/security/pam_google_authenticator.so authtok_prompt=pin

Also server.conf:
plugin /usr/lib64/openvpn/plugins/openvpn-plugin-auth-pam.so "openvpn login: USERNAME Password: PASSWORD pin OTP"

I curious if this version of openvpn community supports google authenticator or do I need to compile it from source. Does anybody know or have better insight?

[dkudos]

These are the errors I get in /var/log/secure:

Dec 2 21:09:48 ip-172-10-2-190 openvpn(pam_google_authenticator)[10712]: debug: start of google_authenticator for "user"
Dec 2 21:09:48 ip-172-10-2-190 openvpn(pam_google_authenticator)[10712]: debug: Secret file permissions are 0400. Allowed permissions are 0600
Dec 2 21:09:48 ip-172-10-2-190 openvpn(pam_google_authenticator)[10712]: debug: "/home/user/.google_authenticator" read
Dec 2 21:09:48 ip-172-10-2-190 openvpn(pam_google_authenticator)[10712]: debug: shared secret in "/home/user/.google_authenticator" processed
Dec 2 21:09:48 ip-172-10-2-190 openvpn(pam_google_authenticator)[10712]: Invalid verification code for user

[dkudos]

On the client which is viscosity I have:
static-challenge "Google Authenticator Code:" 1

[dkudos]

Also to note I have OpenVPN working with viscosity fine with this config:

View OriginalServer Config

port 1194
proto udp
dev tun
sndbuf 0
rcvbuf 0
ca ca.crt
cert server.crt
key server.key
dh dh.pem
plugin /usr/lib64/openvpn/plugins/openvpn-plugin-auth-pam.so openvpn
auth SHA512
tls-auth ta.key 0
topology subnet
server 10.x.0.0 255.255.255.0
ifconfig-pool-persist ipp.txt
reneg-sec 36000
#push "redirect-gateway def1 bypass-dhcp"
push "dhcp-option DNS 172.x.x.x"

# Some Pushed Routes Here
push "route 172.x.0.0 255.255.0.0"

keepalive 10 120
cipher AES-256-CBC
user nobody
group nobody
persist-key
persist-tun
status openvpn-status.log
verb 3
crl-verify crl.pem
log-append /var/log/openvpn.log

[dkudos]

The working PAM config /etc/pam.d/openvpn:

View OriginalPAM Config

auth [user_unknown=ignore success=ok ignore=ignore default=bad] pam_securetty.so
auth required pam_google_authenticator.so forward_pass
auth include system-auth
account include system-auth
password include system-auth

[dkudos]

Then in Viscosity I am using this Client config for a working system:

View OriginalViscosity Config

remote x.x.x.x 1194 udp
nobind
dev tun
persist-tun
persist-key
pull
auth-user-pass
tls-client
ca ca.crt
cert cert.crt
key key.key
remote-cert-tls server
tls-auth ta.key 1
resolv-retry infinite
setenv opt block-outside-dns
rcvbuf 0
cipher AES-256-CBC
auth SHA512
sndbuf 0

[dkudos]

This works in the way that the client opens and it asks you for:

USER
PASSWORD+OTP

example:
User=dude
Password=mypass123456

My problem is that I want to do this:

USER
PASSWORD
OTP

example:
User=dude
Password=mypass
Otp=123456

When I try to do the separate OTP I can config viscosity fine to ask for the OTP separately but what I think the issue lies in my PAM config /etc/pam.d/openvpn. I need your help to get the OTP separate from the PASSWORD passing correctly.

Here is what I see currently as an error when trying to do this verb4 in config FYI:

View OriginalClient Errors

AUTH-PAM: BACKGROUND: received command code: 0
AUTH-PAM: BACKGROUND: USER: user
AUTH-PAM: BACKGROUND: my_conv[0] query='login:' style=2
AUTH-PAM: BACKGROUND: name match found, query/match-string ['login:', 'login'] = 'USERNAME'
AUTH-PAM: BACKGROUND: my_conv[0] query='pin' style=1
AUTH-PAM: BACKGROUND: name match found, query/match-string ['pin', 'pin'] = 'OTP'
AUTH-PAM: BACKGROUND: my_conv[0] query='Password: ' style=1
AUTH-PAM: BACKGROUND: name match found, query/match-string ['Password: ', 'password'] = 'PASSWORD'
AUTH-PAM: BACKGROUND: user 'user' failed to authenticate: Authentication failure
Tue Dec 3 14:40:34 2019 us=757401 x.x.x.x:56947 PLUGIN_CALL: POST /usr/lib64/openvpn/plugins/openvpn-plugin-auth-pam.so/PLUGIN_AUTH_USER_PASS_VERIFY status=1
Tue Dec 3 14:40:34 2019 us=757440 x.x.x.x:56947 PLUGIN_CALL: plugin function PLUGIN_AUTH_USER_PASS_VERIFY failed with status 1: /usr/lib64/openvpn/plugins/openvpn-plugin-auth-pam.so
Tue Dec 3 14:40:34 2019 us=757487 x.x.x.x:56947 TLS Auth Error: Auth Username/Password verification failed for peer
Tue Dec 3 14:40:34 2019 us=780941 x.x.x.x:56947 Control Channel: TLSv1.2, cipher TLSv1/SSLv3 ECDHE-RSA-AES256-GCM-SHA384, 2048 bit RSA
Tue Dec 3 14:40:34 2019 us=780983 x.x.x.x:56947 [user] Peer Connection Initiated with [AF_INET]x.x.x.x:56947
Tue Dec 3 14:40:34 2019 us=784967 x.x.x.x:56947 PUSH: Received control message: 'PUSH_REQUEST'
Tue Dec 3 14:40:34 2019 us=784987 x.x.x.x:56947 Delayed exit in 5 seconds
Tue Dec 3 14:40:34 2019 us=784999 x.x.x.x:56947 SENT CONTROL [user]: 'AUTH_FAILED' (status=1)
Tue Dec 3 14:40:40 2019 us=36751 x.x.x.x:56947 SIGTERM[soft,delayed-exit] received, client-instance exiting

Here is what I am trying in configs ( I have tried quotes and no quotes around plugin group same result ):

Server config (/etc/openvpn/server.conf):

View OriginalServer Config

port 1194
proto udp
dev tun
sndbuf 0
rcvbuf 0
ca ca.crt
cert server.crt
key server.key
dh dh.pem
plugin /usr/lib64/openvpn/plugins/openvpn-plugin-auth-pam.so "openvpn login USERNAME password PASSWORD pin OTP"
#plugin /usr/lib64/openvpn/plugins/openvpn-plugin-auth-pam.so openvpn
auth SHA512
tls-auth ta.key 0
topology subnet
server 10.x.0.0 255.255.255.0
ifconfig-pool-persist ipp.txt
reneg-sec 36000
#push "redirect-gateway def1 bypass-dhcp"
push "dhcp-option DNS 172.x.x.x"

# Some Pushed Routes Here
push "route 172.x.0.0 255.255.0.0"

keepalive 10 120
cipher AES-256-CBC
user nobody
group nobody
persist-key
persist-tun
status openvpn-status.log
verb 4
crl-verify crl.pem
log-append /var/log/openvpn.log

PAM config I am trying to use ( /etc/pam.d/openvpn ):

View OriginalPAM Config

auth [user_unknown=ignore success=ok ignore=ignore default=bad] pam_securetty.so
#auth required pam_google_authenticator.so forward_pass
auth required pam_google_authenticator.so authtok_prompt=pin debug
auth include system-auth
account include system-auth
password include system-auth

Viscosity client config I am using:

View OriginalViscosity Config

remote x.x.x.x 1194 udp
nobind
dev tun
persist-tun
persist-key
pull
auth-user-pass
tls-client
ca ca.crt
cert cert.crt
key key.key
remote-cert-tls server
tls-auth ta.key 1
resolv-retry infinite
setenv opt block-outside-dns
rcvbuf 0
cipher AES-256-CBC
auth SHA512
static-challenge "Google Authenticator Code:" 1
sndbuf 0

[dkudos]

New Update in secure.log:

View OriginalError in Secure Log

Dec 4 14:44:23 ip-172-10-2-190 openvpn(pam_google_authenticator)[13164]: Invalid verification code for user
Dec 4 14:44:23 ip-172-10-2-190 openvpn[13164]: pam_unix(openvpn:auth): authentication failure; logname= uid=0 euid=0 tty= ruser= rhost= user=user

This seems to be the problem. Centos 7 and taking a static-challenge in config is an issue. Again I can config openvpn to do password+otp out of the box and that is fine. But users want to use the viscosity client and save username and pass. Then only enter OTP.

[TinCanTech]

We do not support viscosity here.

[dkudos]

We do not support viscosity here.

Thanks I understand that. I was trying the same config on openvpn client on my android phone with same result. If that makes it easier? I wanted to know if what I was asking was ok on the server side. Or has anyone done this on a Centos 7 box successfully?

[dkudos]

I found the problem:

Centos 7 and other distros most likely have not built from source/master of openvpn. The auth-pam module does not even allow this functionality even in 2.4.8 as noted in README:

View Originalauth-pam

https://github.com/OpenVPN/openvpn/tree ... s/auth-pam

I will build openvpn from source/master then install google auth and try again then note here with progress.

[TinCanTech]

Well, that was a pointless use of a BB code ..

[dkudos]

Well, that was a pointless use of a BB code ..

I apologize yes it was.

I have solved the issue.

[dkudos]

So for Centos 7 and most likely Centos 8 at the time of this writing you have to compile openvpn from source/master not release as openvpn community has not put the change in newest release yet. Mabey I did not see this info but I can not find it anywhere and may be a lack of understanding on my part.

Here is what I did for CentOS 7:

1. cloned the master branch to some working dir on your server

Code: Select all

yum install git
git clone https://github.com/OpenVPN/openvpn.git

2. Install dependencies for build

Code: Select all

yum groupinstall "Development Tools"
yum install pam-devel openssl-devel lzo-devel systemd-devel

3. In the openvpn dir that was cloned

Code: Select all

autoreconf -i -v -f
./configure --enable-systemd
make
make install

4. make sure your config dir for openvpn is /etc/openvpn/server and put config and all in there

5. I copied the systemd file generated in my working dir under distro/systemd/openvpn-server@.service to /etc/openvpn/server/

6. Edie the openvpn-server@.service

Code: Select all

ProtectHome=false

7. I enabled service at this point while in directory my conf file was there already

Code: Select all

systemctl enable openvpn-server@<nameofconffile> . leave off the .conf

8. Start server

Code: Select all

systemctl start openvpn-server@<nameofconffilefromabove>

You will still have to generate certs and setup conf before you do all this. Google authenticator can just be installed via yum and setup like normal. With my configs above and doing this I was able to get viscosity and openvpn client for android to auth like this:

USERNAME
PASSWORD
OTP

Separately so I can save my pass in viscosity and just update OTP anytime I need to login. I will make a more in depth guide and or script to do this but wanted to doc here so people did not waste time like I did trying to find why it was not working. Openvpn does not document this anywhere to my knowledge which could be wrong.

NOTE:
Systemd use is noted here for anyone that wants to know.
https://community.openvpn.net/openvpn/wiki/Systemd

[TinCanTech]

This may be worth reporting as a bug:
https://community.openvpn.net/openvpn/newticket

[dkudos]

Sounds like a plan I will add a ticket for a bug.

[RemoteOne]

For anyone else finding this thread. Thanks to @dkudos for the build instructions. I did some further testing and found that it appears to only be the PAM module that is broken in the latest Centos 7 openvpn package (2.4.8-1.el7). With the standard release installed and configured, I just replaced the PAM plugin in /usr/lib64/openvpn/plugins with the one built from source and the challenge worked as expected. My configuration which used Active Directory authentication via LDAP and the Google Authenticator App

server
plugin /usr/lib64/openvpn/plugins/openvpn-plugin-auth-pam.so "openvpn login USERNAME password PASSWORD pin OTP"

client
static-challenge "GA OpenVPN code:" 1

/etc/pam.d/openvpn
account sufficient pam_ldap.so
account required pam_deny.so

auth requisite /lib64/security/pam_google_authenticator.so authtok_prompt=pin secret=/etc/openvpn/google-authenticator/${USER} user=gauth
auth sufficient pam_ldap.so
auth required pam_deny.so

If you ever did open that ticket, perhaps worth noting on there that it may just be the PAM sources that need updating for the next build.

[EDIT - realised on further testing it was not validating password properly with original PAM config]

[macie]

I tried following your guide but it seems I failed replicating the
"
Username
Password
OTP
"
sequence

using ubuntu server 20.04
downloaded the code from github and followed the instructions you posted, but the command systemctl start openvpn-server@server ended up failing.
did apt install openvpn and systemctl start openvpn-server@server worked.

Username
OTP
works great.
but when tried doing:
Username
password+OTP
I could also skip the password and write just the OTP.

client conf:

View Originalclient.ovpn

client
proto udp
explicit-exit-notify
dev tun
resolv-retry infinite
nobind
persist-key
persist-tun
remote-cert-tls server
ns-cert-type server
static-challenge "Enter Authenticator Code" 1
auth-user-pass
reneg-sec 0
sndbuf 0
rcvbuf 0
auth-nocache
tls-client

my server

View Originalserver.conf

port 42069
proto udp
dev tun
user nobody
group nogroup
persist-key
persist-tun
keepalive 10 120
topology subnet
server 10.8.0.0 255.255.255.0
ifconfig-pool-persist ipp.txt
push "dhcp-option DNS 208.67.220.220"
push "dhcp-option DNS 208.67.222.222"
push "redirect-gateway def1 bypass-dhcp"
client-config-dir /etc/openvpn/server/ccd
status /var/log/openvpn/server/status.log
plugin "/usr/lib/openvpn/openvpn-plugin-auth-pam.so" "openvpn login USERNAME password PASSWORD pin OTP"
log openvpn.log
verb 3

and the pam file is

View Originalopenvpn

auth [success=1 default=ignore] pam_unix.so nullok_secure
auth requisite pam_deny.so
auth required pam_permit.so
auth required /usr/lib/x86_64-linux-gnu/security/pam_google_authenticator.so secret=/etc/openvpn/server/gauth/${USER} user=root debug echo_verification_code authtok_prompt=pin forward_pass

Thank you in advance.