Guide to the Secure Configuration of Debian 11
Rules, Groups, and Values defined within the XCCDF Benchmark
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Disable IPv6 Addressing on All IPv6 Interfaces
To disable support for (<code>ipv6</code>) addressing on all interface add the following line to <code>/etc/sysctl.d/ipv6.conf</code> (or another file in <code>/etc/sysctl.d</code>): <pre>net.ipv6....Rule Medium Severity -
Disable IPv6 Addressing on IPv6 Interfaces by Default
To disable support for (<code>ipv6</code>) addressing on interfaces by default add the following line to <code>/etc/sysctl.d/ipv6.conf</code> (or another file in <code>/etc/sysctl.d</code>): <pre>n...Rule Medium Severity -
Kernel Parameters Which Affect Networking
Thesysctl
utility is used to set parameters which affect the operation of the Linux kernel. Kernel parameters which affect networking and have security implications are described here.Group -
Network Related Kernel Runtime Parameters for Hosts and Routers
Certain kernel parameters should be set for systems which are acting as either hosts or routers to improve the system's ability defend against certain types of IPv4 protocol attacks.Group -
net.ipv4.conf.default.arp_filter
Controls whether the ARP filter is enabled or not. 1 - Allows you to have multiple network interfaces on the same subnet, and have the ARPs for each interface be answered based on whether or not t...Value -
net.ipv4.conf.default.arp_ignore
Control the response modes for ARP queries that resolve local target IP addresses: 0 - (default): reply for any local target IP address, configured on any interface 1 - reply only if the target IP...Value -
net.ipv4.conf.all.shared_media
Controls whether the system can send (router) or accept (host) RFC1620 shared media redirects. <code>shared_media</code> for the interface will be enabled if at least one of conf/{all,interface}/sh...Value -
Verify Permissions on Important Files and Directories
Permissions for many files on a system must be set restrictively to ensure sensitive information is properly protected. This section discusses important permission restrictions which can be verifie...Group -
net.ipv4.conf.default.shared_media
Controls whether the system can send(router) or accept(host) RFC1620 shared media redirects. <code>shared_media</code> for the interface will be enabled if at least one of conf/{all,interface}/shar...Value -
Configure ARP filtering for All IPv4 Interfaces
To set the runtime status of the <code>net.ipv4.conf.all.arp_filter</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.all.arp_filter=<xccdf-1.2:sub idref="xccd...Rule Medium Severity -
Configure Response Mode of ARP Requests for All IPv4 Interfaces
To set the runtime status of the <code>net.ipv4.conf.all.arp_ignore</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.all.arp_ignore=<xccdf-1.2:sub idref="xccd...Rule Medium Severity -
Uncomplicated Firewall (ufw)
The Linux kernel in Ubuntu provides a packet filtering system called netfilter, and the traditional interface for manipulating netfilter are the iptables suite of commands. iptables provide a compl...Group -
Uncommon Network Protocols
The system includes support for several network protocols which are not commonly used. Although security vulnerabilities in kernel networking code are not frequently discovered, the consequences ca...Group -
Ensure No World-Writable Files Exist
It is generally a good idea to remove global (other) write access to a file when it is discovered. However, check with documentation for specific applications before making changes. Also, monitor f...Rule Medium Severity -
Enable Kernel Parameter to Enforce DAC on Symlinks
To set the runtime status of the <code>fs.protected_symlinks</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w fs.protected_symlinks=1</pre> To make sure that the setting is...Rule Medium Severity -
Verify Permissions on Files with Local Account Information and Credentials
The default restrictive permissions for files which act as important security databases such as <code>passwd</code>, <code>shadow</code>, <code>group</code>, and <code>gshadow</code> files must be ...Group -
Verify Group Who Owns Backup group File
To properly set the group owner of/etc/group-
, run the command:$ sudo chgrp root /etc/group-
Rule Medium Severity -
Verify Group Who Owns Backup gshadow File
To properly set the group owner of/etc/gshadow-
, run the command:$ sudo chgrp shadow /etc/gshadow-
Rule Medium Severity -
Verify Group Who Owns Backup passwd File
To properly set the group owner of/etc/passwd-
, run the command:$ sudo chgrp root /etc/passwd-
Rule Medium Severity -
Verify User Who Owns Backup shadow File
To properly set the group owner of/etc/shadow-
, run the command:$ sudo chgrp shadow /etc/shadow-
Rule Medium Severity -
Verify Group Who Owns gshadow File
To properly set the group owner of/etc/gshadow
, run the command:$ sudo chgrp shadow /etc/gshadow
Rule Medium Severity -
Verify Group Who Owns passwd File
To properly set the group owner of/etc/passwd
, run the command:$ sudo chgrp root /etc/passwd
Rule Medium Severity -
Verify Group Who Owns shadow File
To properly set the group owner of/etc/shadow
, run the command:$ sudo chgrp shadow /etc/shadow
Rule Medium Severity -
Verify User Who Owns Backup group File
To properly set the owner of/etc/group-
, run the command:$ sudo chown root /etc/group-
Rule Medium Severity -
Verify User Who Owns Backup gshadow File
To properly set the owner of/etc/gshadow-
, run the command:$ sudo chown root /etc/gshadow-
Rule Medium Severity -
Verify User Who Owns Backup passwd File
To properly set the owner of/etc/passwd-
, run the command:$ sudo chown root /etc/passwd-
Rule Medium Severity -
Verify Group Who Owns Backup shadow File
To properly set the owner of/etc/shadow-
, run the command:$ sudo chown root /etc/shadow-
Rule Medium Severity -
Verify User Who Owns group File
To properly set the owner of/etc/group
, run the command:$ sudo chown root /etc/group
Rule Medium Severity -
Verify User Who Owns gshadow File
To properly set the owner of/etc/gshadow
, run the command:$ sudo chown root /etc/gshadow
Rule Medium Severity -
Verify User Who Owns passwd File
To properly set the owner of/etc/passwd
, run the command:$ sudo chown root /etc/passwd
Rule Medium Severity -
Verify Permissions on Backup group File
To properly set the permissions of/etc/group-
, run the command:$ sudo chmod 0644 /etc/group-
Rule Medium Severity -
Verify Permissions on Backup gshadow File
To properly set the permissions of/etc/gshadow-
, run the command:$ sudo chmod 0640 /etc/gshadow-
Rule Medium Severity -
Verify Permissions on Backup passwd File
To properly set the permissions of/etc/passwd-
, run the command:$ sudo chmod 0644 /etc/passwd-
Rule Medium Severity -
Verify Permissions on Backup shadow File
To properly set the permissions of/etc/shadow-
, run the command:$ sudo chmod 0640 /etc/shadow-
Rule Medium Severity -
Verify Permissions on gshadow File
To properly set the permissions of/etc/gshadow
, run the command:$ sudo chmod 0640 /etc/gshadow
Rule Medium Severity -
Verify Permissions on passwd File
To properly set the permissions of/etc/passwd
, run the command:$ sudo chmod 0644 /etc/passwd
Rule Medium Severity -
Verify Permissions on shadow File
To properly set the permissions of/etc/shadow
, run the command:$ sudo chmod 0640 /etc/shadow
Rule Medium Severity -
Verify Permissions on Files within /var/log Directory
The/var/log
directory contains files with logs of error messages in the system and should only be accessed by authorized personnel.Group -
Verify Group Who Owns /var/log Directory
To properly set the group owner of/var/log
, run the command:$ sudo chgrp root /var/log
Rule Medium Severity -
Verify Group Who Owns /var/log/messages File
To properly set the group owner of/var/log/messages
, run the command:$ sudo chgrp root /var/log/messages
Rule Medium Severity -
Verify Group Who Owns /var/log/syslog File
To properly set the group owner of/var/log/syslog
, run the command:$ sudo chgrp adm /var/log/syslog
Rule Medium Severity -
Verify User Who Owns /var/log Directory
To properly set the owner of/var/log
, run the command:$ sudo chown root /var/log
Rule Medium Severity -
Verify User Who Owns /var/log/messages File
To properly set the owner of/var/log/messages
, run the command:$ sudo chown root /var/log/messages
Rule Medium Severity -
Verify User Who Owns /var/log/syslog File
To properly set the owner of/var/log/syslog
, run the command:$ sudo chown syslog /var/log/syslog
Rule Medium Severity -
Verify Permissions on /var/log Directory
To properly set the permissions of/var/log
, run the command:$ sudo chmod 0755 /var/log
Rule Medium Severity -
Verify Permissions on /var/log/messages File
To properly set the permissions of/var/log/messages
, run the command:$ sudo chmod 0640 /var/log/messages
Rule Medium Severity -
Verify Permissions on /var/log/syslog File
To properly set the permissions of/var/log/syslog
, run the command:$ sudo chmod 0640 /var/log/syslog
Rule Medium Severity -
Verify File Permissions Within Some Important Directories
Some directories contain files whose confidentiality or integrity is notably important and may also be susceptible to misconfiguration over time, particularly if unpackaged software is installed. A...Group -
Verify that System Executable Directories Have Restrictive Permissions
System executables are stored in the following directories by default: <pre>/bin /sbin /usr/bin /usr/sbin /usr/local/bin /usr/local/sbin</pre> These directories should not be group-writable or worl...Rule Medium Severity -
Verify that System Executables Have Root Ownership
System executables are stored in the following directories by default: <pre>/bin /sbin /usr/bin /usr/libexec /usr/local/bin /usr/local/sbin /usr/sbin</pre> All files in these directories should be ...Rule Medium Severity
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