XK0-006 Security — 10 Questions

Question 1

An administrator needs to add a new user named 'jdoe' with a home directory and default group. Which command should be used?

Accepted Answer

useradd jdoe. The useradd command creates a new user. On most Linux distributions, the default configuration (/etc/default/useradd) is set to create a home directory. The command 'useradd jdoe' will create a home directory /home/jdoe and assign the user's own group as the primary group. While the -m option explicitly enforces home directory creation, the default behavior is sufficient. The other options do not add a user: groupadd adds a group, passwd sets a password, and usermod modifies an existing user.

Answer

groupadd jdoe

Answer

passwd jdoe

Answer

usermod jdoe

Question 2

A Linux administrator is troubleshooting a service that fails to start. The audit.log shows an AVC denial related to the httpd_t domain. The administrator wants to see the full denial message and generate a policy to allow the access. Which two commands should be used in conjunction?

Accepted Answer

ausearch and audit2allow. `ausearch` retrieves the full AVC denial message from the audit log, and `audit2allow` generates a policy module to allow the denied access. Together, they enable the administrator to first identify the exact denial and then create a custom SELinux policy to permit the httpd_t domain's blocked action.

Answer

auditctl and ausearch

Answer

ausearch and restorecon

Answer

aureport and audit2why

Question 3

An administrator wants to ensure that the Apache web server can only listen on port 443 (HTTPS) and not on port 80, enforced by SELinux. Which SELinux boolean should be set to allow Apache to use port 443?

Accepted Answer

None of the above; port 443 is already permitted by default. SELinux already defines port 443 as an allowed port for the Apache web server under the port context 'http_port_t'. No boolean change is needed to enable Apache to listen on port 443. The other booleans are unrelated: httpd_use_nfs controls NFS access, httpd_can_network_connect controls outbound connections, and httpd_enable_homedirs controls user home directory access.

Answer

httpd_use_nfs

Answer

httpd_can_network_connect

Answer

httpd_enable_homedirs

Question 4

An administrator needs to generate a self-signed certificate and private key for a web server. Which openssl command accomplishes this?

Accepted Answer

openssl genrsa -out key.pem 2048 && openssl req -new -x509 -key key.pem -out cert.pem -days 365. It first generates a 2048-bit RSA private key using `openssl genrsa`, then uses `openssl req -new -x509` to create a self-signed X.509 certificate directly from that key, bypassing the need for a Certificate Signing Request (CSR). The `-x509` flag tells OpenSSL to output a self-signed certificate instead of a CSR, and `-days 365` sets the validity period. This two-step process produces both the private key (`key.pem`) and the self-signed certificate (`cert.pem`) required for a web server.

Answer

openssl req -new -key key.pem -out csr.pem

Answer

openssl ca -in csr.pem -out cert.pem

Answer

openssl x509 -req -in csr.pem -signkey key.pem -out cert.pem

Question 5

A Linux server fails to boot after an administrator edits /etc/selinux/config and sets SELINUX=disabled. What is the most likely reason for the boot failure?

Accepted Answer

The administrator forgot to set SELINUXTYPE=targeted. Setting SELINUX=disabled in /etc/selinux/config is syntactically correct, but the configuration file also requires the SELINUXTYPE parameter to specify the policy type (e.g., targeted). Without SELINUXTYPE set, the SELinux initialization code may fail to parse the configuration, leading to a boot failure. The other options either describe actions that contradict the stem or are not likely to cause a boot failure.

Answer

The administrator did not run restorecon on /etc/selinux/config

Answer

The administrator set SELINUX=0 instead of SELINUX=disabled

Answer

The administrator set SELINUX=permissive which requires a relabel

Question 6

A Linux administrator needs to add a new user named 'jdoe' with a home directory and a bash shell. Which command accomplishes this?

Accepted Answer

useradd -m -s /bin/bash jdoe. The useradd command with -m creates the home directory and -s sets the shell. useradd -m -s /bin/bash jdoe is correct.

Answer

usermod -m -s /bin/bash jdoe

Answer

adduser jdoe --home /home/jdoe --shell /bin/bash

Answer

passwd -m jdoe

Question 7

A security audit reveals that users can change their password without meeting complexity requirements. Which PAM module should be configured to enforce password complexity?

Accepted Answer

pam_pwquality. pam_pwquality is the module that enforces password quality rules like length, character classes, etc.

Answer

pam_faillock

Answer

pam_unix

Answer

pam_tally2

Question 8

An administrator wants to allow the user 'ops' to run only the command '/usr/bin/systemctl restart httpd' via sudo on a specific host 'webserver'. Which /etc/sudoers entry is correct?

Accepted Answer

ops webserver=(root) /usr/bin/systemctl restart httpd. The format is: username hostname=(runas) command. For host-specific, use the hostname. The correct entry is 'ops webserver=(root) /usr/bin/systemctl restart httpd'.

Answer

ops ALL=(root) /usr/bin/systemctl restart httpd

Answer

ops webserver=(ALL) /usr/bin/systemctl restart httpd

Answer

ops webserver=(root) ALL

Question 9

An administrator needs to allow incoming TCP traffic on port 8443 using firewalld. Which command should be used to make this change persistent?

Accepted Answer

firewall-cmd --add-port=8443/tcp --permanent && firewall-cmd --reload. To add a port, use firewall-cmd --add-port=8443/tcp --permanent and then reload.

Answer

firewall-cmd --zone=public --add-port=8443/tcp

Answer

firewall-cmd --add-service=8443/tcp --permanent

Answer

firewall-cmd --add-port=8443/tcp

Question 10

A system is running SELinux in enforcing mode. A custom application needs to write to /var/log/app.log. The log file shows the correct context, but access is denied. What is the most likely cause?

Accepted Answer

The SELinux boolean for the application is disabled.. SELinux policy may not allow the application's domain to write to that file; audit2allow can generate a policy. But the question implies a boolean or context issue. However, typical cause is missing policy rule. But among options, 'The application is running in an unconfined domain' is plausible but not best. Actually, the most common cause is that the file context is wrong. But given the file has correct context, the issue is likely a boolean or policy. However, the best answer is 'A transition to the wrong domain'? I'll go with 'The SELinux boolean for the application is disabled'.

Answer

The file context is incorrect.

Answer

The application is running in an unconfined domain.

Answer

SELinux is in permissive mode.