Configure a Proper Number of Concurrent Sessions Allowed for a Single SSH Connection

SSH allows a client that supports multiplexing to establish multiple sessions based on a network connection. MaxSessions limits the number of concurrent SSH sessions that can be established for each network connection. This prevents system resources from being occupied by a single connection or a...

Avoid Using Wireless Networks

If the hardware device contains wireless modules such as Wi-Fi and Wi-Fi is enabled in the system, the server may connect to the network wirelessly. If the connection is not managed, the network may be unstable and the attack surface increases. If no wireless network is used, you are advised to...

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...

Disable SysRq

SysRq enables users with physical access to access dangerous system-level commands in a computer. Therefore, it is advised to restrict the usage of the SysRq function. If SysRq is not disabled, you can use the keyboard to trigger SysRq. As a result, commands may be directly sent to the kernel,...

Do Not Install the X Window System

X Window System X for short provides a GUI for users to log in and perform operations in Linux. Generally, servers do not require a GUI. Administrators can configure and modify a server through the CLI. X SPDX-FileCopyrightText: 2025 Greenbone AG Some text descriptions might be excerpted from a...

Restrict the Number of Historical Command Records

HISTSIZE is an environment variable used to control the size of the command history. Specifically, HISTSIZE defines the number of command entries that can be stored in the command history. By setting the value of HISTSIZE, you can limit or increase the size of the command history, thus controllin...

Ensure That the Log Size Limit Is Correct

The size of an audit log file must be limited. The log rotation mechanism can be used to create new log files once the file size limit is reached. If the upper limit is too high, the size of a single log file may be too large, which is inconvenient for management. If the upper limit is too low, t...

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...

Disable the Root User from Logging in to the System Using SSH

The PermitRootLogin parameter in the SSH configuration file /etc/ssh/sshdconfig specifies whether the root user can log in to the system using SSH. The root user is not allowed to log in to the system using SSH. System administrators must use their own user to log in to the system using SSH and r...

Ensure That the User Names Are Unique

The users in /etc/passwd must be unique. If user names in /etc/passwd are duplicate, only the UID of the first user in /etc/passwd is valid. If the administrator runs commands such as useradd to add users, duplicate usernames typically do not exist. However, if the administrator directly modifies...

Configure a Proper Default Zone

The firewalld service allows several independent rule zones to be created on a firewall based on the zone concept. Different interfaces or source addresses can be bound to different zones to implement different control logic. A zone can be configured with many different network interfaces or sour...

Do Not Install the NIS Server

Network Information Service NIS works in client-server mode. NIS clients running the ypbind daemon obtain information from a server. NIS is inherently insecure and is vulnerable to DoS and buffer overflow attacks. Therefore, do not install the NIS server in the service scenario where NIS is not...

Ignore All ICMP Requests

Ignoring all ICMP requests to prohibit external systems from running the ping command to detect the system location. Attackers can detect the URL of the system based on the returned result of the ping command. SPDX-FileCopyrightText: 2025 Greenbone AG Some text descriptions might be excerpted fro...

Enable AIDE

Advanced intrusion detection environment AIDE is an intrusion detection tool that checks the integrity of system files and directories and identifies those maliciously tampered with. In principle, the integrity check can be performed only after an AIDE benchmark database is constructed, which...

Do Not Install the rsync Service

The rsync service can synchronize data between servers or between local drive partitions. However, information leakage risks exist because rsync uses non-encrypted transmission protocols. If the rsync service is enabled and data is transmitted between servers over the network, attackers can...

Do Not Enable the LDAP Service

Lightweight Directory Access Protocol LDAP is a protocol that provides access control and is used to maintain distributed directory information. The LDAP service increases system resource usage and expands the attack surface. If the LDAP service is not required, do not install the LDAP service. T...

Ensure That the Session Timeout Period Is Set Correctly

Setting a proper timeout duration of sessions can reduce the risk of system attacks caused by manual operations of the administrator. To ensure ease of use of the community version in different scenarios, the session timeout interval is not configured in openEuler distributions by default...

Disable the Source Packet Routing

In a network, source routing allows the sender to specify some or all routes for data packets to pass through the network. In regular routing, routers in the network determine the path based on the destination of the data packets. If a large number of packets are tampered with and pass through th...

Correctly Configure the Log Records of Each Service

Logs should be configured so that important system behaviors and security-related information are recorded by rsyslog. The configuration files /etc/rsyslog.conf and /etc/rsyslog.d/.conf specify the rules for logging and the files for recording specific types of logs. If logging is not configured,...

Ensure That Warning Banners Contain Proper Information

Warning banners contain warning information added on the system login page. Security warnings are displayed for all users who log in to the system. The security warnings must include information about the organization to which the system belongs, monitoring or records of login behavior, and legal...

Configure Audit Rules for SELinux

SELinux is a mandatory access control function component of Linux. It is used to implement fine-grained permission control on processes and files. You are advised to audit configurations of SELinux configuration files and policy files and record modification logs. If SELinux audit is not...

Do Not Allow Hidden Executable Files

In Linux, the name of a hidden file starts with a dot .. Hidden executable files are not allowed in the system. Note that . and . are not hidden files. They refer to the current directory and upper-level directory, respectively. The .bashrc, .bashprofile, and .bashlogout files are script files us...

Configure Audit Rules for Privilege Escalation Operations

In openEuler, logs of privilege escalation operations using the sudo command are recorded in the /var/log/secure file by default. This file also records other authentication-related security logs. If you want to audit privilege escalation operations using sudo, you are advised to record logs...

Configure Audit Rules for Time Changes

The system time is essential for the normal running of services. The system time can be changed through synchronization with the time server and manual operations of administrators. The latter is prone to attacks because attackers can change the system time to invalidate some protection policies...

Do Not Enable the NFS Service

The Network File System NFS is one of the earliest and most widely used file systems in UNIX environments. It allows a system to mount file systems of other servers over the network. If the system does not share content through NFS, you are advised to disable NFS to reduce the remote attack...

Configure the Authentication Blocklist and Allowlist Properly

SSH provides the blocklist and allowlist function. You can set a list of users or user groups to allow or deny SSH login for them. By default, this function is not configured in openEuler. The related fields are as follows: AllowUsers userlist specifies the space-separated users who are allowed t...

Configure the chronyd Service Properly

If the time server is incorrectly configured, the time of the local server may be inconsistent with that of other servers or the standard time. If time is incorrect, services that strongly depend on time synchronization, such as market transactions, may be interrupted, and attackers may exploit t...

Configure the Banner Path Correctly

The banner path points to a file which contains the prompt information displayed on the client before a user logs in to the SSH. The content in the file can be configured based on the actual service scenario. If the banner path is not set, no information is displayed by default...

Ensure That Mounting for Unnecessary File System Is Removed

Linux supports multiple file systems through kernel objects loaded to the kernel. As a universal OS platform, openEuler provides various kernel object files in the /lib/modules/kernel version/kernel/fs/ directory to support different file systems. You can run the insmod or modprobe command to loa...

Do Not Preset authorized_keys for the SSH Service

authorizedkeys specifies the public key of the remote host. You can store the public key in the $HOME/.ssh/authorizedkeys file in the home directory for public key authentication. Then you can directly log in to the system. If authorizedkeys is preset in the system and public and private key...

Configure Proper Key Algorithms for User Authentication

If the public and private key authentication mode is used, the public and private key algorithms on the client must be restricted to avoid using insecure algorithms that have been phased out in the industry. The recommended security algorithms are sorted by priority as follows. The algorithms hav...

Ensure That the Group Names Are Unique

The user group names in /etc/group must be unique. If user group names in /etc/group are duplicate, only the GID of the first user group in /etc/group is valid. If the administrator runs commands such as useradd or groupadd to add users or user groups, duplicate user group names typically do not...

Configure a Proper Number of Concurrent Unauthenticated SSH Connections

Without knowing the password, an attacker can set up a large number of concurrent connections that have not been authenticated to consume system resources. The number of concurrent unauthenticated SSH connections is not configured in openEuler by default. You are advised to configure the upper...

Ensure That Passwords Do Not Contain User Names

To ensure user security, you must configure passwords that do not contain user names. If a password is the same as the user name or the user name in reverse order, or contains the user name, attackers can guess the password easily. This requirement is not exerted on passwords of users whose names...

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 Rotation Is Enabled for Audit Logs

maxlogfileaction decides the action taken when the size of a log file reaches the upper limit. By default, ROTATE is configured in openEuler, indicating that a new log file is created when the size of a log file reaches the upper limit and the original log file is not deleted. numlogs specifies t...

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...

Avoid Using USB Storage

USB storage devices are usually used to transfer data between servers. However, in most cases, data on USB storage devices cannot be protected by technical methods, thereby increasing the risk of attacks. Viruses and Trojan horses on USB devices may infect and damage the server. If the USB storag...

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...

Ensure That Removable Device Partitions Are Mounted Using noexec and nodev

The security of removable devices cannot be ensured completely due to a lot of factors, such as the source, usage, and transportation process. In this sense, removable devices are the main host for viruses. Therefore, removable devices must be mounted using noexec and nodev to improve security an...

Do Not Use auditctl to Set auditd Rules

auditd service rules can be configured using either rule files in the /etc/audit/rules.d/ directory applied after server restart or the auditctl command for immediate effect. The permission of the /etc/audit/rules.d/ directory is 750, while that of the auditctl command is 755. Therefore,...

Enable the enforcing Mode

SELinux is a built-in security module in Linux distributions. It controls the access from applications to resources in a fine-grained way, thus improving system security. SELinux can run in any of the following modes: 1. enforcing: If the user does not have the permission to access the resource,...

Ensure That GPG Verification Is Configured for the Yum Repositories

Software packages may be tampered with by attackers during network transmission or local storage. If the integrity verification is not performed on the software packages, software tampered with by attackers may be installed. As a result, the server or even the entire network cluster is attacked. ...

Do Not Enable the rsync Service

The rsync service can synchronize data between servers or between local drive partitions. However, information leakage risks exist because rsync uses non-encrypted transmission protocols. If the rsync service is enabled and data is transmitted between servers over the network, attackers can...

Configure the Remote Log Server

rsyslog can send local logs to a remote log server for unified storage. This facilitates centralized log management, prevents local logs from occupying too much drive space and being tampered with. If remote log storage is not configured, rsyslog logs are stored in local files. As far as the...

Avoid the .netrc File in the Home Directory

The .netrc file stores the passwords for logging in to the remote FTP server. If there are no FTP-related scenarios, you are advised to delete the .netrc file. Passwords stored in the .netrc file are in plaintext and can be easily stolen by attackers. As a result, sensitive data on the FTP server...

Ensure That a Common User Cannot Use pkexec for Privilege Escalation

The pkexec command enables a common user to have the permissions of the superuser or other users. After the authentication is successful, the common user runs the corresponding program with the permissions of the superuser. The pkexec command provides a convenient way for users to change their...

Configure Dumping journald Logs for rsyslog

The system uses journald to collect logs. Logs may be stored on volatile or persistent storage devices. As a result, logs may be lost or the drive space may be used up. In this case, logs need to be dumped in a timely manner to ensure the security of logs and the system. SPDX-FileCopyrightText:...

Ensure That a User Is Locked After a Specified Number of Login Failures

If a user fails to log in to the system for a specified number of consecutive times, the system locks the user. That is, the user is not allowed to log in to the system for a specified period of time to prevent malicious system password cracking. During the lockout period, any input is considered...

Configure Login Audit Rules

The /var/log/lastlog file is updated when a user successfully logs in to the system. Therefore, user login events can be recorded by auditing and monitoring the file. If login audit is not configured, the administrator cannot trace login events from audit logs. By default, login audit rules are n...