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 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 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...

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...

Avoid Using Uncommon Network Services

Some protocols are seldom used and their communities develop slowly. Therefore, related security issues cannot be quickly resolved. If these protocols are not disabled, attackers may exploit the protocols or code vulnerabilities to launch attacks. Stream Control Transmission Protocol SCTP is used...

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...

Enable TCP-SYN Cookie Protection

TCP-SYN cookie protection mitigates the impact of SYN flood attacks on the system. When an attacker launches a SYN flood attack, the half-open connection queue in the kernel is quickly exhausted to block valid connections. If SYN cookie is enabled, the system can still accept valid connections ev...

Do Not Use X11 Forwarding

The X11 forwarding function of SSH allows the GUI program of the remote host to be executed on the local host. If the X11 forwarding function is enabled, the attack surface is expanded and other users on the X11 server may attack the local host. If the function is not required in the service...

Do Not Enable the RPC Service

The rpcbind service maps remote procedure call RPC services to the ports on which they listen. RPC processes notify rpcbind when they start and register the ports they are listening on and the RPC program numbers they expect to serve. The client system then contacts rpcbind on the server using a...

Configure a Proper Value for LoginGraceTime

LoginGraceTime is used to limit the login time of a user. If a user does not complete the login within the time specified by LoginGraceTime, the connection is automatically disconnected. You are advised to set this field to a value less than or equal to 60, in seconds. If this field is set to a...

Do Not Enable the Avahi Service

Avahi is a zero-configuration networking implementation, including a system for multicast DNS/DNS-SD service discovery and automatic broadcast. For example, you can connect a server to the network and use Avahi to automatically broadcast network services running on the server for other user to...

Configure Audit Rules for Privilege-Escalated Commands

Users can call privilege-escalated commands that is, commands with SUID/SGID bits to obtain the super administrator permissions. This operation is risky and often exploited by attackers. You are advised to audit and monitor privilege-escalated commands for future tracing. By default, audit rules...

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...

Configure Proper Policies for INPUT of iptables

The INPUT chain is used to filter packets received from external systems. For any service provided for external systems, configure the corresponding INPUT policy and enable the related port so that external clients can access the service through the port. If the policy is not set, all packets tha...

Do Not Install the Samba Service

The daemon of Samba allows the system administrator to configure the Linux system to share file systems and directories with Windows systems. Samba publishes file systems and directories through the Server Message Block SMB protocol. Windows users will be able to mount these directories and file...

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 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...

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:...

Do Not Install the Avahi Service

Avahi is a zero-configuration networking implementation, including a system for multicast DNS/DNS-SD service discovery and automatic broadcast. For example, you can connect a server to the network and use Avahi to automatically broadcast network services running on the server for other user to...

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...

Do Not Install the FTP Client

File Transfer Protocol FTP is used for file transfer between a Linux server and other servers, desktop systems, as well as terminal devices. FTP does not support encrypted transmission. As a result, data can be easily stolen by attackers during transmission. Therefore, do not install FTP clients ...

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...

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 Proper Association Policies for INPUT and OUTPUT of iptables

Although you can configure protocols, IP addresses, and port numbers to add policies for packets entering and leaving a server to the INPUT and OUTPUT chains, it is difficult to configure suitable policies using the sport parameter due to complicated situations. For example, a client accesses the...

Enable IMA Measurement

Integrity Measurement Architecture IMA is an integrity protection function of the kernel. When IMA is enabled, integrity measurement is provided for important system files based on user-defined policies. The measurement results can be used for local and remote integrity attestation. If IMA is...

Disable the Function of Receiving ICMP Redirect Messages

ICMP redirect messages transmit routing information and notify hosts of a better path through which the hosts send data packets. This is a method for allowing an external routing device to update a system routing table. After both net.ipv4.conf.all.acceptredirects and...

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 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...

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...

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...

Ensure That All Groups Exist in /etc/passwd

All user groups in /etc/passwd must exist in the /etc/group file. If the administrator manually modifies the two files, the user groups may be incorrectly set due to human errors. If a user group in /etc/passwd does not exist in /etc/group, risks of user group permission management may occur...

Configure the SSH Service Log Level Properly

SSH provides multiple log output levels, such as QUIET, FATAL, ERROR, INFO, VERBOSE, DEBUG, DEBUG1, DEBUG2, and DEBUG3. A higher log level such as QUIET or FATAL prints less log information. This saves drive space but hinders administrators from auditing and tracing SSH events. Conversely, a lowe...

Do Not Enable the DHCP Service

The Dynamic Host Configuration Protocol DHCP service provides dynamic allocation of IP addresses to machines. Unless a system is the designated DHCP server, you are advised to disable its DHCP service to reduce the attack surface. SPDX-FileCopyrightText: 2025 Greenbone AG Some text descriptions...

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...

Do Not Install Network Sniffing Tools

If network sniffing tools exist in the production environment, attackers may use them for network analysis and attacks. Therefore, in the production environment, do not install network sniffing, packet capturing, or analysis tools, such as tcpdump, Ethereal, and Wireshark. SPDX-FileCopyrightText:...

Do Not Install the NIS Client

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 client in the service scenario where NIS is not...

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...

Disable the Function of Forwarding ICMP Redirect Messages

ICMP redirects can be used to send routing information to other hosts. As a host itself does not act as a router, it is unnecessary for the host to forward ICMP redirect messages. Attackers can exploit the compromised host to send invalid ICMP redirect messages to other routers, attempting to...

Ensure That the Number of Files That Can Be Opened by Users Is Correctly Configured

The number of files that can be opened in Linux is limited. Once the limit is reached by a user, other users can no longer open files. By default, openEuler limits the maximum number of file handles that can be opened by each user to 1024. If the value exceeds 1024, new file handles cannot be...

Ensure That the Weak Password Dictionary Is Set Correctly

If a user password is weak, it is easy for attackers to guess the password or crack it through dictionary attacks in a short period of time. A weak password dictionary is a collection of passwords that are not strong enough and can be easily cracked through guesses. Weak passwords include default...

Configure Audit Rules for File System Mounting

Generally, for deployed services, the file system mounting does not change. Therefore, any change in the file system mounting may indicate attacks. For file systems with changes in mounting, audit and monitor their mounting conditions for tracing. By default, audit rules for file system mounting...

Configure the Default Policies of nftables to DROP Properly

For security purposes, the nftables base chains INPUT, OUTPUT, and FORWARD are similar to those of iptables. You need to configure the DROP policy for all packets, and then add the ACCEPT policy to the base chains to open related services and ports. If the base chains are not configured or the ho...

Ensure That a User Has Its Own Home Directory

Each user must have its own home directory for storing user-related data. The owner of the home directory must be the user. If the owner of the home directory is not the user, the user cannot read or write the home directory, or the user data stored in the home directory can be read or tampered...

Set the User Validity Period Correctly

The life cycle of a user must be managed based on the application scenario. For example, the life cycle of a temporarily created management or maintenance user or a user required by a periodic service ends when the service life cycle ends. These users should be deleted when their life cycles end...

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...

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...

Configure Proper Cryptographic Algorithms for the SSH Service

As cryptographic technologies develop and computing capabilities improve, some cryptographic algorithms are no longer suitable for today SPDX-FileCopyrightText: 2025 Greenbone AG Some text descriptions might be excerpted from a referenced sources, and are Copyright C by the respective right...

Configure the iptables Policies for Loopback Properly

The loopback address 127.0.0.0/8 is a special address on a server. It is irrelevant to NICs and is mainly used for the inter-process communication of a local device. Packets with the source address 127.0.0.0/8 from NICs should be discarded. If policies related to the loopback address are improper...

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...