Block system vulnerabilities to ensure Linux System Security

As an open operating system, Linux is favored by many programmers. Many senior programmers prefer to write software related to the Linux operating system. This makes the Linux operating system rich in software support, and countless technical staff as technical support, which makes Linux more and more popular for programmers.

However, one of the biggest drawbacks of this open operating system is that each programmer has a different level. After writing the relevant software, you did not pay attention to the vulnerabilities in your own program. There is no unified vulnerability check, which makes it difficult for software developers to detect vulnerabilities in their own programming. However, hackers will pay close attention to these vulnerabilities, these vulnerabilities are used to achieve their own goals. Is the Linux system insecure? In fact, you don't have to worry about it. As long as you do the following, you can use the Linux system with peace of mind.

I. Cancel unnecessary services

In earlier versions of Unix, each different network service had a service program running in the background. Later versions used a uniform/etc/inetd server program. Inetd is short for Internetdaemon. It monitors multiple network ports at the same time. Once it receives connection information from the outside, it executes the corresponding TCP or UDP network service.

Due to the unified command of inetd, Most TCP or UDP services in Linux are set in the/etc/inetd. conf file. Therefore, the first step to cancel unnecessary services is to check the/etc/inetd. conf file and add the "#" sign before the unwanted services.

In general, all services except http, smtp, telnet, and ftp should be canceled, such as the simple File Transfer Protocol tftp, the imap/ipop transport protocol used for network mail storage and receiving, the gopher for data searching, and the daytime and time used for time synchronization.

There are also some services that report system status, such as finger, efinger, systat, and netstat. Although it is very useful for system error detection and user searching, it also provides a convenient portal for hackers. For example, hackers can use the finger service to find users' phones, directories, and other important information. Therefore, many Linux systems cancel all or partially cancel these services to enhance system security.

In addition to setting system service items using/etc/Inetd. conf, inetd also uses the/etc/services file to find the ports used by various services. Therefore, you must carefully check the port settings in the file to avoid security vulnerabilities.

In Linux, there are two different service-type states: one is a service that is executed only when necessary, such as the finger service, and the other is a service that is continuously executed and never paused. This type of service starts to run when the system starts. Therefore, you cannot stop the service by modifying inetd, but you can only modify/etc/rc. d/rc [n]. d/file or use Runleveleditor to modify it. NFS servers that provide file services and news that provide NNTP news services belong to such services. If not necessary, it is best to cancel these services.

Ii. Restrict System Access

Before entering the Linux system, all users need to log on, that is, users need to enter the user account and password. Only after they pass system verification can users enter the system.

Like other Unix operating systems, Linux typically stores passwords in the/etc/passwd file after encryption. All users in Linux can read the/etc/passwd file. Although the password stored in the file has been encrypted, it is still not safe. Generally, users can use the ready-made password cracking tool to guess the password. The safer method is to set the shadow file/etc/shadow and only allow users with special permissions to read the file.

In Linux, to use a shadow file, you must recompile all the utilities to support the shadow file. This method is troublesome. A simple method is to use the plug-in verification module (PAM ). Many Linux systems use Linux tool PAM, which is an identity authentication mechanism that can be used to dynamically change the authentication methods and requirements without re-compiling other utilities. This is because PAM uses a closed package to hide all authentication-related logic in the module, so it is the best helper for using shadow files.

In addition, PAM has many security features: it can rewrite the traditional DES encryption method to other more powerful encryption methods to ensure that user passwords are not easily decrypted; it can set the upper limit for each user to use computer resources; it can even set the user's computer time and location.

Linux administrators can install and set PAM in just a few hours to greatly improve the security of the Linux system and block many attacks outside the system.

3. Maintain the latest system core

Because there are many channels for Linux distribution, and there are often updated programs and system patches, We must update the system kernel frequently to enhance system security.

Kernel is the core of the Linux operating system. It is used to load other parts of the operating system and implement the basic functions of the operating system. As Kernel controls various functions of the computer and network, its security is crucial to the security of the entire system.

Many well-known security vulnerabilities exist in earlier versions of Kernel, which are also unstable. Only versions 2.0.x and later are stable and secure, and the running efficiency of the new versions is greatly improved. When setting the Kernel function, you only need to select the necessary functions. Do not accept all functions as per your order. Otherwise, the Kernel will become large, occupying both system resources and leaving hackers with an opportunity.

There are often the latest security patches on the Internet. Linux administrators should be well-informed and often patronize Security newsgroups to check new patches.

Iv. Enhanced security protection tools

SSH is short for Secure Sockets Layer. It is a set of program groups that can be safely used to replace public programs such as rlogin, rsh, and rcp. SSH uses public key technology to encrypt the communication information between two hosts on the network, and uses its key as an authentication tool.

Because SSH encrypts information on the network, it can be used to securely log on to a remote host and transmit information between the two hosts securely. In fact, SSH not only ensures secure communication between Linux Hosts, but also allows Windows users to Securely connect to Linux servers through SSH.

5. restrict the power of Super Users

As we mentioned above, root is the focus of Linux protection. Because it has unlimited power, it is best not to authorize super users easily. However, the installation and maintenance of some programs must require Super User Permissions. In this case, other tools can be used to grant these users the permissions of some super users. Sudo is such a tool.

The Sudo program allows a general user to log on again with the user's own password after the configuration is set, to obtain the permissions of the Super User, but only a limited number of commands can be executed.

6. Set the security level of the user account

In addition to passwords, user accounts also have security levels, because each account on Linux can be assigned different permissions. Therefore, when a new user ID is created, the system administrator should grant different permissions to the Account as needed and merge them into different user groups.

In tcpd on Linux, you can set the list of persons allowed or not allowed on the computer. You can set the host personnel list in/etc/hosts. allow. The host personnel list cannot be set in/etc/hosts. deny. After the configuration is complete, you need to restart the inetd program to take effect. In addition, Linux automatically records the results that allow or do not allow access to the/rar/log/secure file. The system administrator can identify suspicious access records accordingly.

A dedicated person is responsible for each account ID. In an enterprise, if the employee in charge of an ID leaves the company, the administrator should immediately delete the account from the system. Many intrusion events are borrowed from accounts that have not been used for a long time.

Among the user accounts, hackers prefer root accounts. Such Super Users have the right to modify or delete various system settings, so they can freely access the system. Therefore, you must carefully consider before granting root permissions to any account.

The/etc/securetty file in Linux contains a group of terminal names that can be logged on with the root account. For example, in the RedHatLinux system, the initial value of this file only allows the local virtual console (rtys) to log on with the root permission, but does not allow remote users to log on with the root permission. It is recommended that you do not modify the file. If you must grant the root permission from remote logon, you should first log on with a common account and then use the su command to upgrade to a Super User.

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