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Analyze the inevitability of security vulnerabilities in Unix host systems

◆Security risks of operating system architecture

   This is the root cause of the vulnerability of computer systems. For example, many versions of Unix systems are upgraded and developed by patching, which can also be used by hackers. In addition, operating system programs can be dynamically linked, including I/O drivers and system services, but this also provides opportunities for hackers. For example, hackers can modify the soft link point /dev/rmt/0 of the tape device and add some kind of backdoor program. Then when the user executes tarcvf/dev/rmt/0* commands, the backdoor program may be activated. The occurrence of loopholes. However, the operating system supports program dynamic linking and data dynamic exchange, which are necessary functions for modern operating system integration and expansion, so there are contradictions.

  ◆Procedure creation and remote procedure call (RPC) security risks

   On the one hand, the Unix operating system supports remote loading procedures, on the other hand, it can create processes. Supports the creation and activation of remote processes on network nodes, and the created process can inherit the permissions of the parent process. The combination of these two points makes it possible for hackers to install "spy" software on remote servers.

  ◆The security risks of system daemons

  Daemons are actually a group of system processes. They always wait for the appearance of corresponding conditions. Once the conditions are met, the process continues. Go down. These process characteristics can be exploited by hackers. It is worth noting that the key is not the daemon itself, but whether this daemon has the same rights as the core layer software of the operating system.

   In fact, when Unix was first developed, security was not its main concern. Its security model is designed for small or medium-sized working groups in a local area network environment. The Internet worm incident in 1988 is an obvious evidence: the security measures at the system level are very inadequate. Although the worm incident led to the establishment of the Computer Emergence Response Team (CERT) of Carnegie Mellon University and strengthened the security awareness of system vendors and system administrators, people’s awareness and preparation for security issues still lag far behind. The ability and determination of professional or amateur hackers. Fortunately, there are now many OEM additional security components and third-party products that can provide adequate protection for risk-bearing WWW, FTP, and EmailUnix servers.

  ◆Application software’s lag in security design

   Many applications currently running on the Internet were initially designed with little or no consideration to resist hacker attacks. . The application program of Client/Server structure designed for local area network is directly connected to the Internet environment without any modification, and then faces the attack. Even if these software are protected by firewalls and other security measures, this danger still exists. Practice has shown that no matter how secure an application software may seem, the tools used to develop and run the program and even the components used to protect it may have security vulnerabilities, making the software's security very vulnerable. In other words, software security is a system engineering, and the interacting components of the system must be measured, developed, used and maintained on the unified scale of security. For example, for the system call function get(), if you examine it in isolation, there is no fatal security hole. But when a hacker uses a privileged program to use the get() function to not check the defect of the parameter length, create a buffer overflow, and execute a Shell instead, the ordinary user becomes the root user. It can be seen that in an interactive system, small design flaws can lead to fatal loopholes.

  ◆Difficulties in security assessment of application software

   Due to the large scale and complex design of service software such as WWW and Email running on the Internet, it must be based on theory The above proves that the safety of such complex programs is still a world problem that needs to be broken through with current technical means. Nowadays, the common method of evaluating software security is to detect it in specific use, and even use hackers' attacks to discover software security vulnerabilities and fix them.

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