tailieunhanh - Open Source Security Tools : Practical Guide to Security Applications part 16

Open Source Security Tools : Practical Guide to Security Applications part 16. Few frontline system administrators can afford to spend all day worrying about security. But in this age of widespread virus infections, worms, and digital attacks, no one can afford to neglect network defenses. Written with the harried IT manager in mind, Open Source Security Tools is a practical, hands-on introduction to open source security tools. | Page 129 Thursday June 24 2004 11 11 AM Identifying Security Holes in Your Systems 129 Table Useless Services Services Common Port Numbers Functions chargen 19 Sends a stream of standard characters when polled. Not only isn t this service used anymore but it can also be used to generate a denial of service by having it continually spit out character streams. daytime 13 Returns the time of day. Not really needed for any modern system functions. discard 9 Discards whatever is sent to it silently. Mainly used for testing purposes. echo 7 Replies back with whatever was sent to it. Like chargen echo can be used in denial-of-service attacks by sending it a steady stream of data to echo. finger 79 Much has been said about this service earlier. Very useful to hackers. qotd quote of the day 17 Sends out a little quote or phrase that the system administrator sets up when you log on. Information Leaks When hackers or crackers are looking to get into a system they start by doing some basic reconnaissance. They try to find out as much about your system and network before trying break in. Just like burglars casing a neighborhood they look for the electronic equivalent of lights off newspapers stacking up loose windows and so on. They do this with a number of tools like port scanners and other hacking tools available on the Internet. Unfortunately many operating systems are all too eager to help out these illicit information gatherers. Like chatty doormen they give out vital system information without so much as an ID card. Windows is particularly guilty of these transgressions. Because it was designed to be a plug-and-play network system it offers all kinds of information to any system that polls it with the right commands. As mentioned earlier incorrectly configured DNS servers can also expose a lot of information about your network configuration. Finally an amazing amount of information can be gleaned from using public search engines such as Google. People