Configure Proper MACs Algorithms for the SSH Service

In cryptography, a message authentication code MAC is an authentication mechanism used by communication entities to check message integrity. If the configured algorithms are insecure, security risks increase because weak algorithms have been or are about to be cracked in the industry. The...

Ensure That the Password Protection Is Configured for GRUB

GRUB is the default bootloader of Linux. The bootloader can set the startup mode of the system. By setting the GRUB password, you can prevent attackers from modifying the GRUB setting to enter the single-user mode. If the GRUB password is not set, attackers can easily access the GRUB editing menu...

Configure Audit Rules for File Access Control Permissions

File access permission control is the basic permission management in Linux. Different users can access different files after being authorized. This prevents sensitive information leakage or file data tampering between users and prevents common users from accessing high-permission files or...

Ensure a Firewall Service is Enabled

A firewall is a fundamental security control that enforces mandatory access between networks or systems. Without a firewall, systems are exposed to unauthorized access, data theft, tampering, bandwidth abuse, and malicious traffic. Linux commonly provides three firewall services: firewalld defaul...

Configuring the SSH Service Port Properly

A server typically has multiple NICs and IP addresses. You need to plan IP addresses to determine which ones are used for services or management. Not all IP addresses need to listen on SSH connections. You can specify only some IP addresses to perform SSH connections to reduce the attack surface...

Do Not Preset known_hosts for the SSH Service

knownhosts stores the public keys of the computers that the host has accessed. After a user successfully logs in to another computer, the public key information is automatically saved in $HOME/.ssh/knownhosts. When the same computer is accessed next time, its public key is verified. If the...

Do Not Allow Non-root Users with UID 0

The user with UID 0 is the super administrator user in the Linux system. By convention, the user name is root. The UID of a non-root user cannot be 0. If the UID of the root user is changed to another value and the UID of another user for example, the test user is changed to 0, the test user is...

Configure Audit Rules for Network Environment

Attackers may change the system domain name and host name to launch attacks, such as host spoofing. It is recommended that the user set the audit of system calls setdomainname and sethostname and the audit of the /etc/hosts file to monitor changes in the system domain name and host name. You can...

Ensure That auditd Is Enabled

The auditd component is a user-space component of the Linux audit framework, providing the auditctl, ausearch, and aureport programs to audit and view logs. Audit rules are configured using the auditctl program. When getting started, auditctl reads these rules from /etc/audit/audit.rules. The aud...

Ensure That the Password Validity Is Set Correctly

If a password is not changed for a long time, the password is vulnerable to brute force cracking, which compromises system security. If the password validity period is set too short, the password needs to be changed frequently, increasing management costs. In addition, users may fail to log in...

Do Not Start the debug-shell Service

The debug-shell service is used to locate faults that occur during system boot. This service is installed with systemd. The debug-shell service requires no authentication, that is, attackers can access the root shell by simply pressing Ctrl+Alt+F9 during systemd startup when the OS is booting. Th...

Ensure That the su Command Inherits the User Environment Variables Without Escalating Privileges

The su command enables a common user to have the permissions of the superuser or other users. It is often used for switching the user from a common user to the root user. The su command provides a convenient way for users to change their identities. However, if the su command is run without...

Ensure That Soft and Hard Link Protection Is Correctly Configured

In Linux, a soft or hard link is a file pointing to another file target. In other words, the target is opened once the link file is opened. Therefore, an attacker can forge a soft link as a common user for a privileged user to execute, causing security issues such as privilege escalation. The sam...

Configure the Kernel Parameter ptrace_scope Properly

ptrace is a system call used for process tracing. It provides the capability for a parent process to observe and control child processes. Linux Kernel 3.4 and later versions support completely restricting or disabling the ptrace function. According to the Linux Kernel Yama Documentation, the...

Configure Session Audit Rules

You are advised to audit and monitor the /var/run/utmp, /var/log/wtmp, and /var/log/btmp files. /var/run/utmp records all login events, /var/log/wtmp records all login, logout, shutdown, and restart events, and /var/log/btmp records login failure events. If session audit is not configured,...

Ensure That the umask Value Is Correct

The umask value is the mask for default file or directory permissions. When a file or directory is created, its default permission is set to 777 minus the umask value. For a file, its execute permission is also removed. If the umask value is set improperly, the permission of new files may be too...

Do Not Install Insecure SNMP Versions

Simple Network Management Protocol SNMP is a standard protocol designed to manage network nodes in IP networks. This protocol allows the exchange of network management and control data between network elements NEs. If SNMP is installed in scenarios where SNMP is not required, additional system...

Ensure That the PATH User Variable Is Strictly Defined

In Linux, the PATH variable defines the path for searching for executable files in the user context of the current user. For example, if a user runs the ls command in any directory, the system searches for the ls command in the directories specified by PATH and executes the command. The PATH...

Enable PAM Authentication

Pluggable Authentication Modules PAM on the Linux platform provides a series of open source shared library files .so files. You can flexibly control the authentication process by configuring parameters. After PAM authentication is configured for SSH, the user authentication management module of t...

Configure Audit Rules for File Access Failures

System calls, such as open, truncate, ftruncate, create and openat, are audited and monitored. If the -EACCES or -EPERM error is returned, you lack the permission to access the files. In this case, audit logs need to be recorded. File access failures due to a lack of proper permissions are common...