8

I have a Debian 7 VPS setup. I just enabled SSH Key authentication and disabled password authentication but the disabling did not work.

When I attempt to SSH into my VPS, it prompts me for my SSH Key password which then works fine, BUT if I hit cancel, it will give me "Agent admitted faliure to sign" Error and then it prompts me for the current users account password, I enter it in and it logs me in with my account password, even though it's disabled... Does anyone have any idea why it allows me to login with password access? Thank you

I am connecting with a 4096 bit key.

Here is my sshd_config:

Port 22
# Use these options to restrict which interfaces/protocols sshd will bind to
#ListenAddress ::
#ListenAddress 0.0.0.0
Protocol 2
# HostKeys for protocol version 2
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_dsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key
#Privilege Separation is turned on for security
UsePrivilegeSeparation yes

# Lifetime and size of ephemeral version 1 server key
KeyRegenerationInterval 3600
ServerKeyBits 768
# Logging
SyslogFacility AUTH
LogLevel INFO

# Authentication:
LoginGraceTime 120
PermitRootLogin no
StrictModes yes

RSAAuthentication yes
PubkeyAuthentication yes
#AuthorizedKeysFile     %h/.ssh/authorized_keys

# Don't read the user's ~/.rhosts and ~/.shosts files
IgnoreRhosts yes
# For this to work you will also need host keys in /etc/ssh_known_hosts
RhostsRSAAuthentication no
# similar for protocol version 2
HostbasedAuthentication no
# Uncomment if you don't trust ~/.ssh/known_hosts for RhostsRSAAuthentication
#IgnoreUserKnownHosts yes

# To enable empty passwords, change to yes (NOT RECOMMENDED)
PermitEmptyPasswords no

# Change to yes to enable challenge-response passwords (beware issues with
# some PAM modules and threads)
ChallengeResponseAuthentication no
# Change to no to disable tunnelled clear text passwords
#PasswordAuthentication no

# Kerberos options
#KerberosAuthentication no
#KerberosGetAFSToken no
#KerberosOrLocalPasswd yes
#KerberosTicketCleanup yes

# GSSAPI options
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no
#GSSAPIAuthentication no
#GSSAPICleanupCredentials yes

X11Forwarding yes
X11DisplayOffset 10
PrintMotd no
PrintLastLog yes
TCPKeepAlive yes
#UseLogin no
#MaxStartups 10:30:60
#Banner /etc/issue.net

# Allow client to pass locale environment variables
AcceptEnv LANG LC_*

Subsystem sftp /usr/lib/openssh/sftp-server

# Set this to 'yes' to enable PAM authentication, account processing,
# and session processing. If this is enabled, PAM authentication will
# be allowed through the ChallengeResponseAuthentication and
# PasswordAuthentication.  Depending on your PAM configuration,
# PAM authentication via ChallengeResponseAuthentication may bypass
# the setting of "PermitRootLogin without-password".
# If you just want the PAM account and session checks to run without
# PAM authentication, then enable this but set PasswordAuthentication
# and ChallengeResponseAuthentication to 'no'.
UsePAM yes
Jodka Lemon
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DebianVPS
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    How did you disable the password authentication? Have you restarted sshd after you changed server's configuration? Could you show us your `/etc/ssh/sshd_config`? Please [edit your post](http://unix.stackexchange.com/posts/218034/edit) and add the additional info. – yaegashi Jul 24 '15 at 01:13
  • I put the sshd_config info in the post and yes i restarted sshd afterwards. The formatting got all screwed up but all of the large text had # infront of it (the comment symbol) and theres no issues with the actual formatting in my file – DebianVPS Jul 24 '15 at 01:31
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    Your `PasswordAuthentication no` is commented out... – Jodka Lemon Jul 24 '15 at 01:34

4 Answers4

12

You only disabled ChallengeResponseAuthentication. Lines starting with # are comments and won't interpreted as configuration, they are for humans to read.

To disable all possibilities to login with a password you have to set 

PasswordAuthentication no

AND

ChallengeResponseAuthentication no

There is a possible path over pam_unix to login with a password. This will be disabled with the later.

Jodka Lemon
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6

You should double check if your /etc/ssh/sshd_config file has any Include directive. If so, follow the included files and check if PasswordAuthentication is correctly set.

In my case: Fedora33, my sshd_config file looked like this:

Include /etc/ssh/sshd_config.d/*.conf

...
PasswordAuthentication no
...

But the file: /etc/ssh/sshd_config.d/50-redhat.conf overwrote the PasswordAuthentication option. After changing PasswordAuthentication=no in /etc/ssh/sshd_config.d/50-redhat.conf everything worked as expected.

Catalin Crenguta
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0

You can set number of password prompts to zero as below,

-oNumberOfPasswordPrompts=0

P.S.

Even though this is not relevant to your question, you might also find following useful (especially if you are trying to connect to random IPs).

-oStrictHostKeychecking=no

This will skip key validation with the knownkeys file in the target machine.

I'm using following command to check password-less accessibility to a given user account.

ssh -oStrictHostKeychecking=no -oNumberOfPasswordPrompts=0 <user>@<ip> exit
dr_
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Anubis
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0

The option BatchMode=yes also works to me to disable password authentication.

[oracle@host OHOME1020 /tools/oracle]$ ssh remotehost
oracle@remotehost's password:  [[ <Ctrl-C> pressed... ]]

[oracle@host OHOME1020 /tools/oracle]$ ssh -o BatchMode=yes remotehost
Permission denied (publickey,password).
[oracle@host OHOME1020 /tools/oracle]$  [[ prompt returned promptly ]]
Luis Santos
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