Guide to the Secure Configuration of Debian 11
Rules, Groups, and Values defined within the XCCDF Benchmark
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Verify Permissions on SSH Server Private *_key Key Files
SSH server private keys - files that match the <code>/etc/ssh/*_key</code> glob, have to have restricted permissions. If those files are owned by t...Rule Medium Severity -
Verify Permissions on SSH Server Public *.pub Key Files
To properly set the permissions of/etc/ssh/*.pub, run the command:$ sudo chmod 0644 /etc/ssh/*.pub
Rule Medium Severity -
Remove SSH Server iptables Firewall exception (Unusual)
By default, inbound connections to SSH's port are allowed. If the SSH server is not being used, this exception should be removed from the firewall ...Rule Unknown Severity -
Configure OpenSSH Client if Necessary
The following configuration changes apply to the SSH client. They can improve security parameters relwevant to the client user, e.g. increasing ent...Group -
Configure OpenSSH Server if Necessary
If the system needs to act as an SSH server, then certain changes should be made to the OpenSSH daemon configuration file <code>/etc/ssh/sshd_confi...Group -
SSH RekeyLimit - size
Specify the size component of the rekey limit.Value -
SSH RekeyLimit - size
Specify the size component of the rekey limit.Value -
SSH Compression Setting
Specify the compression setting for SSH connections.Value -
SSH Privilege Separation Setting
Specify whether and how sshd separates privileges when handling incoming network connections.Value -
SSH LoginGraceTime setting
Configure parameters for how long the servers stays connected before the user has successfully logged inValue -
SSH MaxStartups setting
Configure parameters for maximum concurrent unauthenticated connections to the SSH daemon.Value -
Set SSH Client Alive Count Max to zero
The SSH server sends at most <code>ClientAliveCountMax</code> messages during a SSH session and waits for a response from the SSH client. The optio...Rule Medium Severity -
Set SSH Client Alive Count Max
The SSH server sends at most <code>ClientAliveCountMax</code> messages during a SSH session and waits for a response from the SSH client. The optio...Rule Medium Severity -
Set SSH Client Alive Interval
SSH allows administrators to set a network responsiveness timeout interval. After this interval has passed, the unresponsive client will be automat...Rule Medium Severity -
Disable Host-Based Authentication
SSH's cryptographic host-based authentication is more secure than <code>.rhosts</code> authentication. However, it is not recommended that hosts un...Rule Medium Severity -
Allow Only SSH Protocol 2
Only SSH protocol version 2 connections should be permitted. The default setting in <code>/etc/ssh/sshd_config</code> is correct, and can be verifi...Rule High Severity -
Disable Compression Or Set Compression to delayed
Compression is useful for slow network connections over long distances but can cause performance issues on local LANs. If use of compression is req...Rule Medium Severity -
Disable SSH Access via Empty Passwords
Disallow SSH login with empty passwords. The default SSH configuration disables logins with empty passwords. The appropriate configuration is used ...Rule High Severity -
Disable GSSAPI Authentication
Unless needed, SSH should not permit extraneous or unnecessary authentication mechanisms like GSSAPI. <br> The default SSH configuration disallows ...Rule Medium Severity -
Disable Kerberos Authentication
Unless needed, SSH should not permit extraneous or unnecessary authentication mechanisms like Kerberos. <br> The default SSH configuration disallow...Rule Medium Severity -
Disable PubkeyAuthentication Authentication
Unless needed, SSH should not permit extraneous or unnecessary authentication mechanisms. To disable PubkeyAuthentication authentication, add or co...Rule Medium Severity -
Disable SSH Support for .rhosts Files
SSH can emulate the behavior of the obsolete rsh command in allowing users to enable insecure access to their accounts via <code>.rhosts</code> fil...Rule Medium Severity -
Disable X Windows
Unless there is a mission-critical reason for the system to run a graphical user interface, ensure X is not set to start automatically at boot and ...Group -
Disable SSH Support for Rhosts RSA Authentication
SSH can allow authentication through the obsolete rsh command through the use of the authenticating user's SSH keys. This should be disabled. <br><...Rule Medium Severity -
Disable SSH Root Login
The root user should never be allowed to login to a system directly over a network. To disable root login via SSH, add or correct the following lin...Rule Medium Severity -
Disable SSH root Login with a Password (Insecure)
To disable password-based root logins over SSH, add or correct the following line in <code>/etc/ssh/sshd_config</code>: <pre>PermitRootLogin pro...Rule Medium Severity -
Disable SSH TCP Forwarding
The <code>AllowTcpForwarding</code> parameter specifies whether TCP forwarding is permitted. To disable TCP forwarding, add or correct the followin...Rule Medium Severity -
Disable SSH Support for User Known Hosts
SSH can allow system users to connect to systems if a cache of the remote systems public keys is available. This should be disabled. <br><br> To e...Rule Medium Severity -
Disable X11 Forwarding
The X11Forwarding parameter provides the ability to tunnel X11 traffic through the connection to enable remote graphic connections. SSH has the cap...Rule Medium Severity -
Do Not Allow SSH Environment Options
Ensure that users are not able to override environment variables of the SSH daemon. <br> The default SSH configuration disables environment process...Rule Medium Severity -
Enable GSSAPI Authentication
Sites setup to use Kerberos or other GSSAPI Authenticaion require setting sshd to accept this authentication. To enable GSSAPI authentication, add ...Rule Medium Severity -
Enable PAM
UsePAM Enables the Pluggable Authentication Module interface. If set to “yes” this will enable PAM authentication using ChallengeResponseAuthentica...Rule Medium Severity -
Enable Public Key Authentication
Enable SSH login with public keys. <br> The default SSH configuration enables authentication based on public keys. The appropriate configuration is...Rule Medium Severity -
Enable Use of Strict Mode Checking
SSHs <code>StrictModes</code> option checks file and ownership permissions in the user's home directory <code>.ssh</code> folder before accepting l...Rule Medium Severity -
Enable SSH Warning Banner
To enable the warning banner and ensure it is consistent across the system, add or correct the following line in <code>/etc/ssh/sshd_config</code...Rule Medium Severity -
Enable SSH Warning Banner
To enable the warning banner and ensure it is consistent across the system, add or correct the following line in <code>/etc/ssh/sshd_config</code>...Rule Medium Severity -
Enable Encrypted X11 Forwarding
By default, remote X11 connections are not encrypted when initiated by users. SSH has the capability to encrypt remote X11 connections when SSH's <...Rule High Severity -
Limit Users' SSH Access
By default, the SSH configuration allows any user with an account to access the system. There are several options available to limit which users an...Rule Unknown Severity -
Enable SSH Print Last Log
Ensure that SSH will display the date and time of the last successful account logon. <br> The default SSH configuration enables print of the date a...Rule Medium Severity -
Force frequent session key renegotiation
The <code>RekeyLimit</code> parameter specifies how often the session key of the is renegotiated, both in terms of amount of data that may be trans...Rule Medium Severity -
Ensure SSH LoginGraceTime is configured
The <code>LoginGraceTime</code> parameter to the SSH server specifies the time allowed for successful authentication to the SSH server. The longer ...Rule Medium Severity -
System Security Services Daemon (SSSD) - LDAP
The System Security Services Daemon (SSSD) is a system daemon that provides access to different identity and authentication providers such as Red H...Group -
Set LogLevel to INFO
The INFO parameter specifices that record login and logout activity will be logged. <br> The default SSH configuration sets the log level to INFO. ...Rule Low Severity -
Set SSH Daemon LogLevel to VERBOSE
The <code>VERBOSE</code> parameter configures the SSH daemon to record login and logout activity. To specify the log level in SSH, add or correct t...Rule Medium Severity -
Set SSH authentication attempt limit
The <code>MaxAuthTries</code> parameter specifies the maximum number of authentication attempts permitted per connection. Once the number of failur...Rule Medium Severity -
Set SSH MaxSessions limit
The <code>MaxSessions</code> parameter specifies the maximum number of open sessions permitted from a given connection. To set MaxSessions edit <co...Rule Medium Severity -
Ensure SSH MaxStartups is configured
The MaxStartups parameter specifies the maximum number of concurrent unauthenticated connections to the SSH daemon. Additional connections will be ...Rule Medium Severity -
Enable Use of Privilege Separation
When enabled, SSH will create an unprivileged child process that has the privilege of the authenticated user. To enable privilege separation in SSH...Rule Medium Severity -
Strengthen Firewall Configuration if Possible
If the SSH server is expected to only receive connections from the local network, then strengthen the default firewall rule for the SSH service to ...Group -
System Security Services Daemon
The System Security Services Daemon (SSSD) is a system daemon that provides access to different identity and authentication providers such as Red H...Group
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