6.2. Technical Security

This chapter contains SIMP security concepts that are related to the technical security controls described in NIST 800-53.

6.2.1. Identification and Authentication

This section addresses the identification and authentication of users and devices.

6.2.2. User Identification and Authentication

Identification and authentication of system and service users can occur at either the Operating System level or globally in the SIMP architecture. While local accounts and groups can be created manually, the SIMP team suggests adding users using the native Puppet user and group types. System users can authenticate their access using Secure Shell (SSH) keys or passwords. For more centralized control, identify and authenticate users by using the Lightweight Directory Access Protocol (LDAP). [IA-2]

The SIMP team recommends using LDAP as the primary source for user management and provides a functional default OpenLDAP configuration for this purpose. LDAP and Pluggable Authentication Modules (PAM) work together closely and, with the default SIMP configuration, the PAM settings are enforced on top of the LDAP settings for two layers of control. Due to this partnership, items such as account lockouts may need to be reset on both the local system and the LDAP server. If the suggested settings in the SIMP-provided default LDAP Directory Interchange Formats (LDIF) are not used, implementations must ensure that security is maintained through manual procedures. Use of group accounts for users is strongly discouraged. System services may need to have accounts, but all of these should be managed by Puppet using the user and group native types. [IA-2 (5)].

6.2.3. Device Identification and Authentication

Devices are identified by a Media Access Control (MAC) address prior to receiving an IP address via the Dynamic Host Configuration Protocol (DHCP). In the default SIMP architecture, IP addresses are fixed mappings to their associated MAC address (i.e., not assigned dynamically). There is no authentication for the binding of MAC addresses to IP addresses due to the nature of the DHCP protocol.

Device authentication occurs through the mapping of the MAC to the IP through the internally controlled DHCP and the mapping of the IP to the host name through the internally controlled Domain Name System (DNS) service for each individual Puppet client. After kickstart, each client system generates an internal cryptographic identifier and communicates that information with the Puppet server to be approved by an administrator at a later time. All further communication between the Puppet server and the clients over the Puppet protocol is encrypted subsequently and authenticated with this identifier. Automatic approval can be set up in tightly controlled environments; however, this option is not suggested for open environments. [IA-3, IA-3 (3)]

6.2.4. Identifier Management

Managing user identifiers (also known as user names) involves administrative procedures that are unique for each implementation. Disabling unused local accounts is the only control that SIMP can enforce technologically. In this case, if an account has an expired password that has not been changed 35 days after expiration, the account will be disabled. If a user does not have a password (e.g., he or she only authenticates with SSH keys), then there is no inherent technological mechanism for enforcement due to the nature of the software. [IA-4e.]

6.2.5. Authenticator Management

Authenticators for users are passwords and/or SSH keys; the management of each is implementation specific. SSH keys do not expire; therefore, implementations must provide a procedure for removing invalid keys. Removing public keys from LDAP is one practical solution.

When using passwords, local and LDAP passwords provided for users should be set to change at first login. This is the default in the SIMP-provided LDIFs. Once a user attempts to change a password, the settings in PAM and LDAP enforce complexity requirements.

For the default password complexity rules see the What is the Password Complexity for SIMP? FAQ.

[IA-5, IA-5 (1), IA-5 (4)]

Password aging and history is enforced through a combination of PAM and LDAP. By default, the previous 24 passwords cannot be reused.

[IA-5 (1)(e)]

There are a number of default passwords in SIMP that are required for installation. Each implementation requires the user to change the default passwords and protect the new passwords. In addition, there are embedded passwords within the SIMP system that are used due to a lack of software-supported alternatives.

Please see the SIMP User Guide for additional information.

6.2.6. Access Control

This section describes the various levels of access control, including account management, access enforcement, information flow enforcement, separation of duties, least privilege, session controls, permitted actions without identification and authentication, security attributes, and remote access.

6.2.7. Account Management

Account management procedures should be created and maintained for each implementation of SIMP. The procedures should include the information listed in NIST 800-53 control AC-2. SIMP has the mechanisms in place to enforce most account management policies. The mechanisms for account management have several default settings including:

  • Central account management using OpenLDAP. [AC-2 (1)]
  • Password expiration.
    • Local accounts expire 35 days after password expiration. [AC-2 (3)]
    • LDAP accounts do not expire automatically due to inactivity; implementations should audit LDAP accounts regularly.
  • Auditing of administrative actions to capture local account creation and modifications to LDAP accounts is done via the /var/log/slapd_audit.log file and /var/log/audit/audit.log for local accounts. [AC-2 (4)]
  • Shell sessions timeout after 15 minutes of inactivity. [AC-2 (5)]
    • This can be circumvented by running a command that opens an endless pipe such as /bin/cat. However, this command cannot be enforced more heavily due to the high likelihood of breaking system applications. If the optional gnome module is used, the GNOME screen saver will lock the screen after 15 minutes of inactivity.
  • Assignment of users into groups locally or centrally via LDAP. [AC-2 (7)]
    • By default, SIMP will have an administrators groups that has the ability to run sudosh. Implementations should further define administrators or user groups and limit them with the Puppet sudo class.

6.2.8. Access Enforcement

SIMP uses the implementation of Discretionary Access Control (DAC) that is native to Linux. Specific file permissions have been assigned based on published security guidance for Red Hat, CentOS, and UNIX.

Default permissions on files created by users are enforced with user file access mask settings (using the umask command) that allow only the owner to read and write to the file. Implementations may further extend the access control in UNIX by restricting access to application files or using the file Access Control List (ACL) commands getfacl and setacl. Users of SIMP should not change file permissions on operating system files as it may decrease the overall security of the system. If a group needs access to a particular file or directory, use the setfacl command to allow the necessary access without lessening the permissions on the system. [AC-3]

6.2.9. Information Flow Enforcement

IPTables on each SIMP system is controlled by the IPTables Puppet module. When developing a new module, the IPTables rules needed for an application should be included with the module by calling the appropriate methods from the IPTables module. The end result should be a running IPTables rule set that includes the default SIMP rules and any rules needed for applications. The default communications allowed are included in Default Server Ports and Default Client Ports. [AC-4] Default Server Ports

Application Direction Protocol Transport Ports Comment
Puppet Localhost HTTP TCP 8140 The port upon which the Puppet master listens for client connections via Apache
Puppet CA In HTTPS TCP 8141 This is used to ensure that Apache can verify all certificates from external systems properly prior to allowing access to Puppet.
Apache/YUM In HTTP TCP 443 This is used for YUM and is encrypted using https.
DHCPD In DHCP/BOOTP TCP/UDP 546,547 DHCP pooling is disabled by default and should only be used if the implementation requires the use of this protocol.
TFTP In TFTP TCP/UDP 69 This is used for kickstart. It could also be used to update network devices. TFTP does not support encryption.
rsyslog Out syslog TCP/UDP 6514 This is encrypted when communicating with a SIMP syslog server (not installed by default).
named In/Out DNS TCP/UDP 53 Inbound connections happen to the locally managed hosts. Outbound connections happen to other domains per the normal operations of DNS.
NTPD Out NTP TCP/UDP 123 Only connects to an external time source by default.
SSHD In SSH TCP 22 SSH is always allowed from any source IP by default.
stunnel In TLS TCP 8730 Stunnel is a protected connection for rsyncing configuration files to Puppet clients.
rsync Localhost RSYNC TCP 873 This accepts connections to the localhost and forwards through Stunnel.
LDAP In LDAP TCP 389 Connections are protected by bi-directional, authenticated encryption.
LDAPS In LDAPS TCP 636 Used for LDAP over SSL. Default Client Ports

Application Direction Protocol Transport Ports Comment
Puppet Out HTTPS TCP 8140 Communications to the Puppet server.
rsyslog Out syslog TCP/UDP 6514 This is encrypted when communicating with a SIMP syslog server.
DNS Client Out DNS TCP/UDP 53 Normal name resolution.
NTPD Out NTP TCP/UDP 123 Only connects to an external time source by default.
SSHD In SSH TCP 22 SSH is allowed from any source IP by default.
LDAP Out LDAP TCP 389 Connections are protected by bi-directional authenticated encryption.

6.2.10. Separation of Duties

SIMP enforces separation of duties using account groups. Groups are created with each implementation to separate roles or duties properly. The SIMP team recommends that this management be done using the posixGroup object in LDAP for full OS support. [AC-5]

6.2.11. Least Privilege

SIMP does not allow root to directly SSH into a system. Direct access to the root user must occur via a console (or at a virtual instance of the physical console) to log on. Otherwise, users must log on as themselves and perform privileged commands using sudo or sudosh. [AC-6]

NIST 800-53 least privilege security controls give people access to objects only as needed. SIMP provides only the needed software, services, and ports to allow the system to be functional and scalable. The system then relies on a given implementation to perform proper account management and user role assignments. [AC-6]

6.2.12. Session Controls

SIMP provides a number of security features for sessions. These features include:

  • Accounts are locked after five invalid log on attempts over a 15 minute period. The account is then locked for 15 minutes. No administrator action is required to unlock an account. [AC-7]
  • System banners are presented to a user both before and after logging on. The default banner should be customized for each implementation. [AC-8]
  • After a successful log on, the date, time, and source of the last log on is presented to the user. The number of failed log on attempts since the last log on is also provided. [AC-9 and AC-9 (1)]
  • A limit of 10 concurrent SSH sessions are allowed per user. This can be further limited if an implementation decides it is set too high. Given the way SSH is used in most operational settings, this default value is reasonable. [AC-10]
  • Session lock only applies if the windowmanager::gnome module is used. Sessions lock automatically after 15 minutes of inactivity. Users must authenticate their access with valid credentials to reestablish a session. [AC-11]

6.2.13. Permitted Actions Without Identification and Authentication

SIMP has a number of applications that do not require both identification and authentication. These services are listed below along with an explanation of why these aspects are not required. Implementations should include any additional services that do require identification and/or authentication. [AC-14]

Service/Application Rationale
TFTP TFTP is a simple file transfer application that, in the SIMP environment, does not allow for writing to the files being accessed. This application is primarily used to support the Preboot Execution Environment (PXE) booting of hosts and the updating of network devices. There is no option to authenticate systems at this level by protocol design. TFTP is limited to a user’s local subnet using IPtables and is enforced additionally with TCPWrappers.
DHCP By default, system IP addresses are not pooled, but are rather statically assigned to a client, which is identified by the MAC address. DHCP is limited to the local subnet.
Apache/YUM RPMs are stored in a directory for systems to use for both kickstart and package updating. Sensitive information should never be stored here. Apache/YUM is limited to the local subnet.
DNS The DNS protocol does not require identification nor authentication. DNS is limited to the local subnet.

Table: Actions Without Identification and Authentication

6.2.14. Security Attributes

SELinux is fully enforcing, in targeted mode, in SIMP. SELinux is an implementation of Mandatory Access Control. It can be set to enforcing mode during the SIMP configuration or turned on at a later time. All of the SIMP packaged modules have been designed to work with SELinux set to enforcing. [AC-16]

6.2.15. Remote Access

Remote access in SIMP is performed over SSH, specifically using the OpenSSH software. OpenSSH provides both confidentiality and integrity of remote access sessions. The SSH IPTables rules allow connections from any host. SSH relies on other Linux mechanisms to provide identification and authentication of a user. As discussed in the auditing section, user actions are audited with the audit daemon (auditd) and sudosh. [AC-17]

6.2.16. Systems and Communications Protection

The following sections provide information regarding application partitioning, shared resources, and various levels of protection for systems and communications.

6.2.17. User and Administration Application Separation (Application Partitioning)

SIMP can be used in a variety of ways. The most common is a platform for hosting other services or applications. In that case, there are only administrative users present. Users with accounts will be considered as a type of privileged user.

SIMP can also be used as a platform for workstations or general users performing non-administrative activities. In both cases, general users with accounts on an individual host are allowed access to the host using the pam::access module, so long as they have an account on the target host. No user may perform or have access to administrative functions unless given sudo or sudosh privileges via Puppet.

6.2.18. Shared Resources

There are several layers of access control that prevent the unauthorized sharing of resources in SIMP. Account access, operating system DAC settings, and the use of PKI collectively prevent resources from being shared in ways that were not intended. [SC-4]

6.2.19. Denial of Service Protection

SIMP has limited ability to prevent or limit the effects of Denial of Service (DoS) attacks. The primary measures in place are to drop improperly formatted packets using IPTables and Kernel configurations such as SYN cookies. [SC-5]

6.2.20. Boundary Protection

SIMP does not provide boundary protection. [SC-7]

6.2.21. Transmission Security

SIMP traffic is protected with protocols that provide confidentiality and integrity of data while in transit. The tables in Information Flow Enforcement describe the protocols used to encrypt traffic and explain the protocols that cannot be protected at the transmission layer. SSH, and TLS all provide data transmission integrity and confidentiality. The software that controls them on Red Hat and CentOS are OpenSSH and OpenSSL. The SIMP team takes industry guidance into consideration when configuring these services. For example, the list the cryptographic ciphers available is limited to the highest ciphers that SIMP needs. All others are disabled. [SC-8, SC-9, SC-23, SC-7]

6.2.22. Single User Mode

SIMP systems have a password requirement for single user mode. In the event maintenance needs to be performed at a system console, users must be in possession of the root password before they can be authenticated. Bootloader passwords are also set to prevent unauthorized modifications to boot parameters. [SC-24]

6.2.23. PKI and Cryptography

SIMP has two native certificate authorities. The first is known as Fake CA. A local certificate authority is used to create properly formed server certificates if an implementation does not have other means of obtaining them. Many SIMP services require certificates; therefore, SIMP provides this tool for testing or for situations where other certificates are not available. The second certificate authority, Puppet CA, is built into Puppet. Puppet creates, distributes, and manages certificates that are specifically for Puppet.

The Fake CA certificates should be replaced with your own hardware-generated certificates if at all possible. The Puppet CA may be replaced but please understand all ramifications to the infrastructure before doing so.

More information on the Puppet CA can be found in the Puppet Labs security documentation. [SC-17, SC-13]


Fake CA certificates should not be used in an operational setting unless no better options are available.

6.2.24. Mobile Code

SIMP does not use mobile code; however, there are not any particular tools that will prevent its use. [SC-18]

6.2.25. Protection of Information at Rest

SIMP provides the capability to enable Full Disk Encryption (FDE) by default. However, in the interest of automated reboots, the initial randomly generated key is baked into the initrd. Please see the Disk Encryption section of the Installation Guide for details. [SC-28]

6.2.26. Audit and Accountability

This section discusses the content, storage, and protection of auditable events.

6.2.27. Auditable Events

Auditd and Rsyslog provide the foundation for SIMP auditing. Auditd performs the majority of the security-related events; however, other Linux logs also have security information in them and are captured using rsyslog.

The default auditable events for SIMP were developed based on several industry best practices including those from the SCAP Security Guide and several government configuration guides. The suggested rules by those guides were fine-tuned so the audit daemon would not fill logs with useless records or reduce performance. These guides should be referenced for a detailed explanation of why rules are applied. Additional justification can be found in the comments of the SIMP audit rules found in the appendix of this guide. [AU-2]

The SIMP development team reviews every release of the major security guides for updated auditable events suggestions. Each of those suggestions is reviewed and applied if deemed applicable. [AU-2 (3)]

Privileged commands are audited as part of the SIMP auditing configuration. This is accomplished by monitoring sudo commands with auditd. Session interaction for administrators that use sudosh are also logged. Each sudosh session can be reviewed using sudosh-replay and are also sent to rsyslog. [AU-2 (4)]

6.2.28. Content of Audit Records

Audit records capture the following information [AU-3]:

  • Date and Time
  • UID and GID of the user performing the action
  • Command
  • Event ID
  • Key
  • Node Hostname/IP Address
  • Login Session ID
  • Executable

6.2.29. Audit Storage

Audit logs are stored locally on a separate partition in the /var/log directory. The size of this partition is configurable. Other default audit storage configurations include:

  • A syslog log is written when the audit partition has 75MB free. (This can be changed to e-mail, if an e-mail infrastructure is in place.) [AU-5a., AU-5 (1)]
  • The log file rotates once it reaches 30MB.

6.2.30. Audit Reduction and Response

SIMP provides a means to capture the proper information for audit records and stores them centrally. Each implementation must decide and document how it reduces, analyzes, and responds to audit events. [AU-5]

Auditd, like all services in SIMP, is controlled by Puppet. Stopping the service without disabling Puppet means the service will always be started automatically during a Puppet run. The files that control the audit configuration will also revert to their original state if changed manually on a client node. In the event auditd fails, the system will continue to operate. Several security guides have suggested that the system should shut down if auditd fails for any reason. To prevent operational issues, SIMP will not shut down, but will provide an alert via syslog when this happens. [AU-5 (1)]

SIMP also comes with an optional module for the Elasticsearch/Logstash/Grafana (ELG) stack. These three open source tools can be combined to parse, index, and visualize logs. There are also SIMP provided dashboards for the Kibana web interface. Implementations can build their own dashboards to meet local security or functional needs for log reduction and management. [AU-6]

See Elasticsearch, Logstash, and Grafana for more information.

6.2.31. Protection of Audit Information

The primary means of protecting the audit logs is through the use of file permissions. Audit records are stored in the /var/log directory and can only be accessed by root. Audit logs are rotated off daily if the implementation has not developed a way of offloading the logs to another location where they can be backed up. Lastly, if the rsyslog::stock::log_server module is implemented, logs are transmitted to the log server over a TLS protected link.

6.2.32. Time Synchronization

Each SIMP client (including the Puppet Master) has ntpd enabled by default. Part of the installation directs the clients to a time server. If no servers are available, the SIMP clients can use the Puppet Master as the central time source. Audit logs receive their time stamp from the local server’s system clock; therefore, the SIMP client must be connected to a central time source for timestamps in audit logs to be accurate.