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Guide to the Secure Configuration of Ubuntu 20.04

Rules, Groups, and Values defined within the XCCDF Benchmark

  • net.ipv4.conf.all.accept_source_route

    Trackers could be using source-routed packets to generate traffic that seems to be intra-net, but actually was created outside and has been redirected.
    Value
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  • 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
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  • 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
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  • net.ipv4.conf.all.log_martians

    Disable so you don't Log Spoofed Packets, Source Routed Packets, Redirect Packets
    Value
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  • net.ipv4.conf.all.rp_filter

    Enable to enforce sanity checking, also called ingress filtering or egress filtering. The point is to drop a packet if the source and destination IP addresses in the IP header do not make sense whe...
    Value
    Show

  • net.ipv4.conf.all.secure_redirects

    Enable to prevent hijacking of routing path by only allowing redirects from gateways known in routing table. Disable to refuse acceptance of secure ICMP redirected packets on all interfaces.
    Value
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  • 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
    Show

  • net.ipv4.conf.default.accept_redirects

    Disable ICMP Redirect Acceptance?
    Value
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  • net.ipv4.conf.default.accept_source_route

    Disable IP source routing?
    Value
    Show

  • net.ipv4.conf.default.log_martians

    Disable so you don't Log Spoofed Packets, Source Routed Packets, Redirect Packets
    Value
    Show

  • 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
    Show

  • net.ipv4.icmp_echo_ignore_broadcasts

    Ignore all ICMP ECHO and TIMESTAMP requests sent to it via broadcast/multicast
    Value
    Show

  • net.ipv4.icmp_ignore_bogus_error_responses

    Enable to prevent unnecessary logging
    Value
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  • net.ipv4.tcp_syncookies

    Enable to turn on TCP SYN Cookie Protection
    Value
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  • Disable Accepting ICMP Redirects for All IPv4 Interfaces

    To set the runtime status of the <code>net.ipv4.conf.all.accept_redirects</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.all.accept_redirects=0</pre> To mak...
    Rule Medium Severity
    Show

  • Disable Kernel Parameter for Accepting Source-Routed Packets on all IPv4 Interfaces

    To set the runtime status of the <code>net.ipv4.conf.all.accept_source_route</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.all.accept_source_route=0</pre> ...
    Rule Medium Severity
    Show

  • 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
    Show

  • 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
    Show

  • Enable Kernel Parameter to Log Martian Packets on all IPv4 Interfaces

    To set the runtime status of the <code>net.ipv4.conf.all.log_martians</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.all.log_martians=1</pre> To make sure t...
    Rule Unknown Severity
    Show

  • Disable Kernel Parameter for Accepting Secure ICMP Redirects on all IPv4 Interfaces

    To set the runtime status of the <code>net.ipv4.conf.all.secure_redirects</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.all.secure_redirects=0</pre> To mak...
    Rule Medium Severity
    Show

  • Disable Kernel Parameter for Accepting ICMP Redirects by Default on IPv4 Interfaces

    To set the runtime status of the <code>net.ipv4.conf.default.accept_redirects</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.default.accept_redirects=0</pre...
    Rule Medium Severity
    Show

  • Disable Kernel Parameter for Accepting Source-Routed Packets on IPv4 Interfaces by Default

    To set the runtime status of the <code>net.ipv4.conf.default.accept_source_route</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.default.accept_source_route=...
    Rule Medium Severity
    Show

  • Enable Kernel Paremeter to Log Martian Packets on all IPv4 Interfaces by Default

    To set the runtime status of the <code>net.ipv4.conf.default.log_martians</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.default.log_martians=1</pre> To mak...
    Rule Unknown Severity
    Show

  • Enable Kernel Parameter to Use Reverse Path Filtering on all IPv4 Interfaces by Default

    To set the runtime status of the <code>net.ipv4.conf.default.rp_filter</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.default.rp_filter=1</pre> To make sure...
    Rule Medium Severity
    Show

  • Remove ufw Package

    The ufw package can be removed with the following command: 
    $ apt-get remove ufw
    Rule Medium Severity
    Show

  • Enable Kernel Parameter to Ignore ICMP Broadcast Echo Requests on IPv4 Interfaces

    To set the runtime status of the <code>net.ipv4.icmp_echo_ignore_broadcasts</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.icmp_echo_ignore_broadcasts=1</pre> To...
    Rule Medium Severity
    Show

  • Enable Kernel Parameter to Ignore Bogus ICMP Error Responses on IPv4 Interfaces

    To set the runtime status of the <code>net.ipv4.icmp_ignore_bogus_error_responses</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.icmp_ignore_bogus_error_response...
    Rule Unknown Severity
    Show

  • Enable Kernel Parameter to Use TCP Syncookies on Network Interfaces

    To set the runtime status of the <code>net.ipv4.tcp_syncookies</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.tcp_syncookies=1</pre> To make sure that the settin...
    Rule Medium Severity
    Show

  • Network Parameters for Hosts Only

    If the system is not going to be used as a router, then setting certain kernel parameters ensure that the host will not perform routing of network traffic.
    Group
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  • Disable Kernel Parameter for Sending ICMP Redirects on all IPv4 Interfaces by Default

    To set the runtime status of the <code>net.ipv4.conf.default.send_redirects</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.conf.default.send_redirects=0</pre> To...
    Rule Medium Severity
    Show

  • Disable Kernel Parameter for IP Forwarding on IPv4 Interfaces

    To set the runtime status of the <code>net.ipv4.ip_forward</code> kernel parameter, run the following command: <pre>$ sudo sysctl -w net.ipv4.ip_forward=0</pre> To make sure that the setting is per...
    Rule Medium Severity
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  • Nftables Base Chain Hooks

    The possible hooks which can be used to configure the base chain are: <code>ingress</code> (only in netdev family since Linux kernel 4.2, and inet family since Linux kernel 5.10): sees packets imm...
    Value
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  • Nftables Chain Names

    The rules in nftables are attached to chains. Unlike in iptables, there are no predefined chains like INPUT, OUTPUT, etc. Instead, to filter packets at a particular processing step, a base chain ...
    Value
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  • Nftables Base Chain Policies

    This is the default verdict that will be applied to packets reaching the end of the chain (i.e, no more rules to be evaluated against). Currently there are 2 policies: <code>accept</code> this ve...
    Value
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  • Nftables Base Chain Priorities

    Each nftables base chain is assigned a priority that defines its ordering among other base chains, flowtables, and Netfilter internal operations at the same hook. For example, a chain on the prer...
    Value
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  • Nftables Base Chain Types

    Base chains are those that are registered into the Netfilter hooks, i.e. these chains see packets flowing through the Linux TCP/IP stack. The possible chain types are: <code>filter</code>, which i...
    Value
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  • Nftables Families

    Netfilter enables filtering at multiple networking levels. With iptables there is a separate tool for each level: iptables, ip6tables, arptables, ebtables. With nftables the multiple networking l...
    Value
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  • Nftables Master configuration file

    The file which contains top level configuration for nftables service, and with which, the service is started.
    Value
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  • Nftables Tables

    Tables in nftables hold chains. Each table only has one address family and only applies to packets of this family. Tables can have one of six families.
    Value
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  • Verify ufw Enabled

    The ufw service can be enabled with the following command: 
    $ sudo systemctl enable ufw.service
    Rule Medium Severity
    Show

  • Uninstall nftables package

    nftables is a subsystem of the Linux kernel providing filtering and classification of network packets/datagrams/frames and is the successor to iptables. The <code>nftables</code> package can be rem...
    Rule Medium Severity
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  • Verify nftables Service is Enabled

    The nftables service allows for the loading of nftables rulesets during boot, or starting on the nftables service The <code>nftables</code> service can be enabled with the following command: <pre>...
    Rule Medium Severity
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  • Verify nftables Service is Disabled

    nftables is a subsystem of the Linux kernel providing filtering and classification of network packets/datagrams/frames and is the successor to iptables. The <code>nftables</code> service can be dis...
    Rule Medium Severity
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  • Ensure nftables Rules are Permanent

    nftables is a subsystem of the Linux kernel providing filtering and classification of network packets/datagrams/frames. The nftables service reads the <xccdf-1.2:sub xmlns:xccdf-1.2="http://checkli...
    Rule Medium Severity
    Show

  • Ensure Base Chains Exist for Nftables

    Tables in nftables hold chains. Each table only has one address family and only applies to packets of this family. Tables can have one of six families. Chains are containers for rules. They exist i...
    Rule Medium Severity
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  • Set nftables Configuration for Loopback Traffic

    Configure the loopback interface to accept traffic. Configure all other interfaces to deny traffic to the loopback network.
    Rule Medium Severity
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  • Ensure a Table Exists for Nftables

    Tables in nftables hold chains. Each table only has one address family and only applies to packets of this family. Tables can have one of six families.
    Rule Medium Severity
    Show

  • 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
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  • Install ufw Package

    The ufw package can be installed with the following command: 
    $ apt-get install ufw
    Rule Medium Severity
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  • Ensure ufw Default Deny Firewall Policy

    A default deny policy on connections ensures that any unconfigured network usage will be rejected. Note: Any port or protocol without a explicit allow before the default deny will be blocked.
    Rule Medium Severity
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