Configure TIME_WAIT for TCP

TIMEWAIT indicates the time for TCP to wait for connection destruction. If this parameter is set to a large value, a large number of TCP connections are not closed and DoS attacks occur. You are advised to set this parameter to a value less than or equal to 60. SPDX-FileCopyrightText: 2025...

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...

Configure the Scripts Executed by crontab to Be Writable Only by Their Owners

crontab is the configuration file used by the system to execute scheduled tasks. The path of the configuration file is /etc/crontab. With crontab, the OS automatically executes the tasks defined by the administrator based on service requirements. Therefore, the execution scripts or programs...

Ensure That Partitions without Executable Files Are Mounted Using noexec

A data drive only stores data generated during service running. No command is executed in the data drive. Therefore, you can mount the drive or partition using noexec to improve security and reduce the attack surface. SPDX-FileCopyrightText: 2025 Greenbone AG Some text descriptions might be...

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...

Do Not Install 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...

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...

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 a Proper SSH Service Authentication Mode

A proper authentication mode helps ensure user and system data security. Typically, the user/password authentication mode is suitable for human-machine users. In non-interactive login scenarios, the public and private keys are suitable for authentication. In high-risk scenarios, only the public 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...

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...

Avoid Using Programs Labeled unconfined_service_t

The purpose of setting the unconfinedservicet label for SELinux is to enable some third-party service processes not configured with SELinux policies to run without restrictions. By default, when systemd runs a third-party application whose label is bint or usrt generally located in directories su...

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 PermitUserEnvironment

PermitUserEnvironment allows users to set SSH environment variables, which may be exploited by attackers to launch attacks. If PermitUserEnvironment is set to yes, attackers can modify SSH environment variables to evade the security mechanism or execute attack code. This configuration must be...

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,...

Configure sudoers Audit Rules

The sudo command allows common users to perform privileged operations as the root user, which is highly risky. Though attackers cannot access the root user easily, they can escalate the privilege using the sudo command. You are advised to configure audit for the /etc/sudoers file and the...

Configure Audit Rules for User Information Changes

Generally, for deployed services, users and user groups do not change. Passwords, however, are changed periodically but not frequently due to validity periods. It is recommended that key authentication and authorization data be audited and monitored so that changes can be traced. Performing attac...

Ensure That the Security Level of the Global Encryption Policy Is Not Lower than DEFAULT

The global encryption/decryption policy of the system is used to specify the algorithms supported by the encryption and decryption components. You can change the preset security policy level by modifying the /etc/crypto-policies/config configuration file to change the algorithm set that can be us...

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...

Configure Kernel Parameter kptr_restrict Properly

kptrrestrict is used to protect kernel symbol addresses. When the protection level is low, common users can obtain kernel symbol addresses, which are easy to be exploited by attackers. This increases the attack surface and reduces system security. Currently, kptrrestrict can be set to any of 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...

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...

Drive Data Should Be Managed in Partitions

When installing the OS, plan different partitions for OS data and service data based on the scenario. Do not store all data in the same drive or partition. Properly planning drive partitions avoids or reduces the following risks: 1. Log files are too large and use up the space of the service driv...

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...

Log Spoofing Source Routing and Redirect Packets

Logging spoofing, source routing, and redirect packets sent to the system helps discover attack sources and formulate protection measures. SPDX-FileCopyrightText: 2025 Greenbone AG Some text descriptions might be excerpted from a referenced sources, and are Copyright C by the respective right...

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:...

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...

Do Not Install the Telnet Client

Telnet is an application-layer protocol and is usually used for remote login, operation control, and system modification of servers. Telnet data is not encrypted, and user names, passwords, and transmitted data can be easily stolen by attackers. Therefore, do not install or use Telnet clients. Us...

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...

Do Not Enable Login Capabilities for Users Who Are Not Meant for Direct Login

Typically, a Linux system has multiple users, not all of which are used for login. For instance, some users are automatically created during the installation of software packages like systemd and dhcp. These users serve specific purposes, such as running related software services. It is essential...

Configure the SELinux Policy Correctly

SELinux policies are classified into basic policies and user-defined policies. Basic policies: policies defined in the basic policy package, including selinux-policy, selinux-policy-targeted, and selinux-policy-mls. User-defined policies: policies modified or added by users. SELinux can implement...

Enable the haveged Service

The haveged service can generate an unpredictable stream of random numbers in a simple way. These random numbers can fill the system entropy pool, which can solve the problem of low system entropy in some cases. You are advised to enable this service to meet the needs of encryption, decryption, o...

Do Not Install the HTTP Service

HyperText Transfer Protocol HTTP is a simple request-response protocol and usually runs over TCP. It specifies what messages the client may send to the server and what responses the client receives. Request and response messages include headers in ASCII, and the message content often uses a...

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...

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...

Configure the Rotate Policy in rsyslog

rsyslog collects logs from the system and records them in files. logrotate copies and compresses log files periodically and quantitatively to ensure that log files do not occupy too many drive resources or even cannot be maintained. If the rotate policy is not configured for log files, they will...

Do Not Enable the DNS Service

The Domain Name System DNS is a hierarchical naming system that maps names to IP addresses of computers, services, and other network resources. Unless a system is the designated DNS server, you are advised to disable its DNS service to reduce the attack surface. SPDX-FileCopyrightText: 2025...

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...

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...

Ensure That User Group and Password File Permissions Are Correct

In the Linux OS-related information, such as users, passwords, and user groups, is recorded in the configuration files in the /etc directory. Proper permissions must be set for accessing these files. Otherwise, the files may be stolen or tampered with by attackers. The owner and owner group of...

Do Not Install Debugging Tools

Debugging scripts and tools in the service environment may be exploited by attackers to launch attacks. Therefore, do not install any debugging tools or files in the production environment. Such tools or files include but not limited to: code debugging tool privilege escalation commands, scripts,...

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...

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...

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...

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...

Configure a Proper Number of Queues in the SYN_RECV State

The SYNRECV queue stores the TCP connection requests that have not been confirmed by the peer end. A larger value indicates more waiting network connections. If the value is too small, the system is vulnerable to TCP SYN flood attacks. As a result, normal connections are denied. If the value is t...

Discard Forged ICMP Packets and Do Not Record Logs

Setting icmpignoreboguserrorresponses to 1 prevents the kernel from recording responses to duplicate broadcast packets, which prevents useless log information from filling in the file system. Some attackers send ICMP packets that violate RFC-1122 and attempt to fill the log file system with a lar...

Configure Proper Policies for INPUT of nftables

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...

Configure a Proper SSH Service Authentication Mode

A proper authentication mode helps ensure user and system data security. Typically, the user/password authentication mode is suitable for human-machine users. In non-interactive login scenarios, the public and private keys are suitable for authentication. In high-risk scenarios, only the public a...

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,...