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 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 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 Configure Deprecated Options for the SSH Service

Currently, the SSH service communication protocols are classified into the first generation and the second generation. The configuration options of the SSH service of different versions are incompatible. In addition, the configuration options of some earlier versions are deprecated in the new...

Avoid Using the root User to Access the System Locally

Users with the root permission can access all Linux resources. If the root user is used to log in to the Linux OS to perform operations, there are many potential security risks. To avoid the risks, do not use the root user to log in to the Linux OS. If necessary, indirectly use the root user...

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...

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...

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...

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...

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 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...

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...

Ensure That the LD_LIBRARY_PATH Environment Variable Is Correctly Defined

LDLIBRARYPATH is an environmental variable in Linux. When loading a dynamic link library, the program preferentially obtains the library from the path specified by LDLIBRARYPATH. Generally, LDLIBRARYPATH should not be set, because a maliciously set value will make the program link to an incorrect...

Configure the Core Dump Properly

A core dump records the memory status when a program stops abnormally or breaks down. It helps locate faults but may contain sensitive information in the process memory. In some cases, the core dump function needs to be enabled to record problem causes. When enabling the core dump function,...