The SSH daemon must not permit Kerberos authentication unless needed.

Overview

Finding ID	Version	Rule ID	IA Controls	Severity
V-22475	GEN005526	SV-35075r1_rule	ECSC-1	Low

Description
Kerberos authentication for SSH is often implemented using GSSAPI. If Kerberos is enabled through SSH, the SSH daemon provides a means of access to the system's Kerberos implementation. Vulnerabilities in the system's Kerberos implementation may then be subject to exploitation. To reduce the attack surface of the system, the Kerberos authentication mechanism within SSH must be disabled for systems not using this capability.

Description

Kerberos authentication for SSH is often implemented using GSSAPI. If Kerberos is enabled through SSH, the SSH daemon provides a means of access to the system's Kerberos implementation. Vulnerabilities in the system's Kerberos implementation may then be subject to exploitation. To reduce the attack surface of the system, the Kerberos authentication mechanism within SSH must be disabled for systems not using this capability.

STIG	Date
HP-UX 11.31 Security Technical Implementation Guide	2016-12-20

Details

Check Text ( C-34939r1_chk )
Check the SSH daemon configuration. Note that keywords are case-insensitive and arguments (args) are case-sensitive. keyword=KerberosAuthentication arg(s)=no Default values include: "no" Note: When the default "arg" value exactly matches the required "arg" value (see above), the entry is not required to exist (commented or uncommented) in the ssh (client) or sshd (server) configuration file. While not required, it is recommended that the configuration file(s) be populated with all keywords and assigned arg values as a means to explicitly document the ssh(d) binary's expected behavior. If the system does not use Kerberos authentication, this is not applicable. Examine the file. # cat /opt/ssh/etc/sshd_config \| tr '\011' ' ' \| tr -s ' ' \| sed -e 's/^[ \t]*//' \| grep -v '^#' \| grep -i "KerberosAuthentication" If the return value is yes, this is a finding.

Check Text ( C-34939r1_chk )

Check the SSH daemon configuration. Note that keywords are case-insensitive and arguments (args) are case-sensitive.

keyword=KerberosAuthentication
arg(s)=no

Default values include: "no"

Note: When the default "arg" value exactly matches the required "arg" value (see above), the entry is not required to exist (commented or uncommented) in the ssh (client) or sshd (server) configuration file. While not required, it is recommended that the configuration file(s) be populated with all keywords and assigned arg values as a means to explicitly document the ssh(d) binary's expected behavior.

If the system does not use Kerberos authentication, this is not applicable.

Examine the file.
# cat /opt/ssh/etc/sshd_config | tr '\011' ' ' | tr -s ' ' | sed -e 's/^[ \t]*//' | grep -v '^#' | grep -i "KerberosAuthentication"

If the return value is yes, this is a finding.

Fix Text (F-30245r1_fix)
Edit the SSH daemon configuration and set (add if necessary) a KerberosAuthentication directive set to no.