Overly broad permissions can turn one compromised account into a much larger security problem. Learn how to reduce unnecessary access, review privileges, and apply least privilege across modern Linux systems. Review Linux Privileges×
Looking to improve the security of your Linux server to protect against vulnerabilities and attacks? Here's a checklist to live by. . This article includes a collection of commands and best practices that you can use to improve the security of your Linux servers (RHEL/CentOS). If you have more suggestions, please mention them in the comments. Enjoy the read! . Explore valuable strategies and optimal methods to strengthen your Linux server protection and reduce vulnerabilities.. Linux Server Best Practices, Security Enhancement Tips, Risk Management. . Brittany Day
This article is excerpted from The Official Ubuntu Book by Benjamin Mako Hill, Jono Bacon, Corey Burger, Jonathan Jesse and Ivan Krstic, copyright Prentice Hall. Reprinted with permission of Prentice Hall, all rights reserved. . As a system administrator, one of your chief tasks is dealing with server security. If your server is connected to the Internet, for security purposes, it's in a war zone. If it's only an internal server, you still need to deal with (accidentally) malicious users, disgruntled employees and the guy in accounting who really wants to read the boss's secretary's e-mail. The link for this article located at Computer World is no longer available. . As a system operator, discover crucial strategies to bolster your Ubuntu Linux server's defenses against potential risks.. Ubuntu Server Security,System Administration Tips,Server Protection. . LinuxSecurity Contributors
Here's a really good article by Steve Bellovin and others from CERT that attempt to provide "risk management" instead of "risk avoidance" . . Here's a really good article by Steve Bellovin and others from CERT that attempt to provide 'risk ma. here's, really, article, steve, bellovin, others, attempt, provide, 'risk. . Anthony Pell
This document describes another method for intrusion detection. It is based on a proactive ruleset as opposed to reactive ruleset.. . This document describes another method for intrusion detection. It is based on a proactive ruleset a. document, describes, another, method, intrusion, detection, based, proactive, ruleset. . Anthony Pell
Reducing the risk of intrusion can be achieved by eliminating many of the known common problems. . The vast majority of attacks on done by script kiddies who scan massive IP blocks looking for a vulnerable computer, then run a program which they don't understand, to exploit the vulnerability they've just discovered. To block these script kiddies just fix the common vulnerabilities that the programs they use rely on. Buffer Overflow A buffer overflow attack is when the attacker sends malformed packets to a service that causes the memory buffer to overflow. The cracker hopes this will cause the program to crash and defaulting into a root prompt. Buffer overflows happen because of programming errors where input was not checked to be valid. To prevent buffer overflows, all code must be meticulously hand checked multiple times by multiple people. Since this is not often possible, to limit the chances of being successfully cracked by a buffer overflow attack, make sure you keep your systems up to date and get rid of all excess services. Reducing the number of total services your server is offering, the less amount of code that could have a potential buffer overflow. Also, there are kernel patches that prevent some forms of buffer overflow. Denial of Service A Denial of Service, DoS, attack can come in many shapes and forms. The Blue Screen of Death from Windows can be one if it is caused by someone and not just poor programming. Also, the infamous DDoS attacks from earlier this year are an example where multiple 'zombie' computers coordinate together to attack a host all at the same time. A DoS attack is anything that maliciously prevents the computer from doing what was intended. This is usually accomplished by errors in code that will cause the program to eat up all the system resources. Preventing DoS attacks in like preventing buffer overflows, but a firewall will also help with this, unlike buffer overflows. Another page with firewall information can be found here Trojan Horse A Trojan Horseis a program that purports to do something useful when in fact it really does something malicious such as send off the password file to a remote system. It must first be explicitly placed there by a malicious user. This is typically done to ensure that once a cracker has exploited a weakness in your system he has a way back into the system at a later date, even after the initial vulnerability has been fixed. If a trojan is on the system, chances are the system has been cracked and needed to be wiped and reinstalled. The only way to prevent trojans is with a good firewall. A firewall works for blocking trojans only if the firewall is set to default deny and only essensial services are allow through the firewall. If a Linux system is cracked with mal-intent, and not just to see if the cracker could, then there will most likely be a root kit on the system. A very common trojan port is 31337; it should probably be blocked on all systems, with email notification if anyone tried to connect to it. IP Session Hi-Jacking IP Session Hi-Jacking, also known as a man in the middle attack, is a sophisticated attack which can now be done using tools circulating in the script kiddie community. With an IP Session Hi-Jacking, an user connects to a system using a service like telnet, then a cracker intercepts the packets and tricks the system into thinking that the cracker's machine is actually the user's machine. The user will think her connect got dropped, when in actuality, it is still going, but it has been taken over by the cracker. With this form of attack, there is no way to block it, but there are checks that can be done to prevent it. Telnet is the type of service that crackers want to hi-jack; it has shell access, is unencrypted, and doesn't perform many checks to make sure the person really is who they say they are. SSH, on the other hand, would be very hard to hi-jack; it has strong encryption, multiple checks of an identity, and can have its shell access limited. Most services can't really be hi-jacked, butthe ones that can, like telnet, usually have a secure replacement, like SSH, that can be used instead. IP Spoofing IP Spoofing attacks involves the attacker falsifying the sender IP address so that other computers think the packet came from a different system. This type of attack can be useful in two different ways. First, if an service uses only IP-based authentication, then with IP spoofing, an attacker could use a service that isn't designated for him to use. The second way this type of attack could be used is similar to the first, but is different because it is used in conjunction with another form of attack. For example, a script kiddie knows there is a FTP server running that has a DoS vulnerability in it, but only the company's president's home computer's IP is allowed past the firewall to access the FTP server. With IP spoofing, the script kiddie could trick the firewall into thinking the packets are from the president's home computer and activate the DoS vulnerability. Conclusion While fixing these problems can be time consuming, great programs like Bastille Linux are around to make it much easier. This overview of Bastille Linux and also a walkthrough to installing it. But even with Bastille Linux and programs like it, security will always be a process not a program, and it will always take time to properly secure a system. Resources CERT IP Spoofing Attacks and Hijacked Terminal Connections -- This document summarizes both the IP spoofing technique that can lead to root access on a system and the tool that intruders are using to take over open terminal and login connections after they get root access. CERT smurf IP Denial of Service Attacks -- This document provides some background on ICMP and describes the two main components to the smurf denial-of-service attack, the use of forged ICMP echo request packets and the direction of packets to IP broadcast addresses. CERT TCP SYN Flooding and IP Spoofing Attacks -- This document provides a brief outline of the problem and apartial solution. daemon9, Project Neptune -- A comprehensive analysis of TCP SYN flooding. daemon9, IP-spoofing Demystified -- explain IP-spoofing to the masses. It assumes little more than a working knowledge of Unix and TCP/IP. Oh, and that yur not a moron... Ten Security Measures Against DDoS Bennet Todd's Distributed Denial of Service Attacks document. . Enhance security and minimize intrusion risks by adopting a multi-faceted approach that targets common vulnerabilities with effective strategies.. Intrusion Prevention Strategies, Cyber Threat Mitigation, System Security Tips. . Anthony Pell
The BIOS is the lowest level of software that configures or manipulates your x86-based hardware.. LILO and other Linux boot methods access the BIOS to determine how to boot up your Linux machine. Other hardware that Linux runs on has similar software (OpenFirmware on Macs and new Suns, Sun boot PROM, etc...). You can use your BIOS to prevent attackers from rebooting your machine and manipulating your Linux system. Most PC BIOSs let you set a boot password. This doesn't provide all that much security (the BIOS can be reset, or removed if someone can get into the case), but might be a good deterrent (i.e. it will take time and leave traces of tampering). Similarly, on SPARC/Linux (Linux for SPARC(tm) processor machines), your EEPROM can be set to require a boot-up password. This might slow attackers down. Many PC BIOSs also allow you to specify various other good security settings. Check your BIOS manual or look at it the next time you boot up. For example, most BIOSs disallow booting from floppy drives and some require passwords to access some BIOS features. Note: If you have a server machine, and you set up a boot password, your machine will not boot up unattended. Keep in mind that you will need to come in and supply the password in the event of a power failure. ;(. To secure the BIOS and Linux boot process, adopt strategies like BIOS password protection, boot order configuration, and secure boot features for enhanced safety. BIOS Security, Linux Boot Process, Security Strategies, System Protection. . Anthony Pell
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