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cis-ubuntu2004-v300-5-1-10

DevOps & Security
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Ensure sshd HostbasedAuthentication is disabled

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Source SKILL.md: https://github.com/CyberStrikeus/CyberStrike/blob/HEAD/.cyberstrike/skill/CIS_benchmarks/Operating_Systems/Ubuntu/CIS_Ubuntu_Linux_20.04_LTS_Benchmark_v3.0.0/cis-ubuntu2004-v300-5-1-10/SKILL.md

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Ensure sshd HostbasedAuthentication is disabled (Automated)

Profile Applicability

  • Level 1 - Server
  • Level 1 - Workstation

Description

The HostbasedAuthentication parameter specifies if authentication is allowed through trusted hosts via the user of .rhosts, or /etc/hosts.equiv, along with successful public key client host authentication.

Rationale

Even though the .rhosts files are ineffective if support is disabled in /etc/pam.conf, disabling the ability to use .rhosts files in SSH provides an additional layer of protection.

Audit Procedure

Command Line

Run the following command to verify HostbasedAuthentication is set to no:

# sshd -T | grep hostbasedauthentication

hostbasedauthentication no
  • IF - Match set statements are used in your environment, specify the connection parameters to use for the -T extended test mode and run the audit to verify the setting is not incorrectly configured in a match block. Example additional audit needed for a match block for the user sshuser:
# sshd -T -C user=sshuser | grep hostbasedauthentication

Note: If provided, any Match directives in the configuration file that would apply are applied before the configuration is written to standard output. The connection parameters are supplied as keyword=value pairs and may be supplied in any order, either with multiple -C options or as a comma-separated list. The keywords are addr (source address), user (user), host (resolved source host name), laddr (local address), lport (local port number), and rdomain (routing domain)

Expected Result

hostbasedauthentication no

Remediation

Command Line

Edit the /etc/ssh/sshd_config file to set the HostbasedAuthentication parameter to no above any Include and Match entries as follows:

HostbasedAuthentication no

Note: First occurrence of a option takes precedence, Match set statements withstanding. If Include locations are enabled, used, and order of precedence is understood in your environment, the entry may be created in a file in Include location.

Default Value

HostbasedAuthentication no

References

  1. SSHD_CONFIG(5)
  2. SSHD(8)
  3. NIST SP 800-53 Rev. 5: CM-1, CM-2, CM-6, CM-7, IA-5

CIS Controls

v8 - 5.2 Use Unique Passwords Use unique passwords for all enterprise assets. Best practice implementation includes, at a minimum, an 8-character password for accounts using MFA and a 14-character password for accounts not using MFA.

v7 - 4.4 Use Unique Passwords Where multi-factor authentication is not supported (such as local administrator, root, or service accounts), accounts will use passwords that are unique to that system.

MITRE ATT&CK Mappings: T1078, T1078.001, T1078.003 | TA0001 | M1042