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...

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...

Do Not Install the Print Service

A server running Common Unix Printing System CUPS provides print services to other devices on the network. Running the CUPS service requires additional system resources and expands the attack surface. Therefore, do not start the CUPS service in the scenario where the CUPS service is not required...

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...

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 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...

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,...

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...

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...

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...

Do Not Install Python 2

The EOL for Python 2 was reached on January 1, 2020, and there will be no updates and maintenance. If you continue to use Python 2, the system attack surface may be expanded, and system vulnerabilities and attack risks may increase. Therefore, do not use Python 2. If Python is required, you are...

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...

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 Proper SSH Key Exchange Algorithms

Key exchange is a process in which two parties exchange keys to allow the use of an encryption algorithm. A secure key exchange algorithm enables them to securely exchange keys, thereby using encryption algorithms to encrypt messages to be sent and decrypt received messages. Set the SSH key...

Disable IP Forwarding

If a node does not function as a gateway server, disable the IP forwarding function. Otherwise, attackers can use the node as a router. In the container scenario, if network packets need to be forwarded through the host, IP forwarding is allowed. SPDX-FileCopyrightText: 2025 Greenbone AG Some tex...

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...

Ensure That the Unnecessary SUID/SGID Bit on a File Is Deleted

SUID set user ID and SGID set group ID are special permission bits used to control program permissions in UNIX and UNIX-like OSs, including Linux. It is important to ensure that files do not contain unnecessary SUID or SGID bits to improve system security. These bits allow files to run with the...

Ensure That Users Are Required to Change Their Passwords Upon the First Login

If a password, such as one reset by an administrator, is not promptly changed in the service environment when it is not set by the user, it may lead to low-cost attacks. Therefore, it is necessary for users to change their password upon their initial login. However, the root user...

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...

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...