Softpanorama

May the source be with you, but remember the KISS principle ;-)
Home Switchboard Unix Administration Red Hat TCP/IP Networks Neoliberalism Toxic Managers
(slightly skeptical) Educational society promoting "Back to basics" movement against IT overcomplexity and  bastardization of classic Unix

Logging access attempts with TCP Wrappers

TCP_wrappers write a message into your system logs every time a connection is requested, whether it is granted access or not. These entries in the logs above are reason enough to have TCP_wrappers installed on your system. The messages are written through the standard syslog facility and by default go to the same place as mail transactions. On my Linux distribution, Caldera Network Desktop based on Red Hat Linux, the default has been changed so that the messages are written to the same log file as other daemons (LOG_DAEMON facility).

Option fields let administrators easily change the log facility and priority level for a rule by using the severity directive.

In the following example, connections to the SSH daemon from any host in the example.com domain are logged to the the default authpriv facility (because no facility value is specified) with a priority of emerg:

sshd : .example.com : severity emerg

It is also possible to specify a facility using the severity option. The following example logs any SSH connection attempts by hosts from the example.com domain to the local0 facility with a priority of alert:

sshd : .example.com : severity local0.alert

In any event, when someone accesses my machine via telnet, a message like this is placed in the /var/log/messages:

Apr 9 17:24:58 ads in.telnetd[15339]: connect from somewhere.else.com

If the connection was refused, the message would read:

Apr 9 17:25:15 ads in.telnetd[15604]: refused connect from someother.place.com
If I want to see all the telnet attempts in my log, I can simply type the command:
grep telnetd /var/log/messages
TCP_wrappers can give me even more information through the use of “booby traps”. TCP_wrappers can be configured to run shell commands when certain services are requested. Let's assume I have reason to suspect someone at nasty.badguy.com is trying to use the Trivial FTP program (TFTP) to steal my password file. In my /etc/hosts.deny file, I can put the following line (this example is straight from the hosts_access(5) man page that comes with TCP_wrappers):
in.tftpd : nasty.bad-guy.com : ( /usr/sbin/safe_finger -l @%h |\ /bin/mail -s %d->%h root) &
Access to TFTP is denied to all users from nasty.badguy.com. In addition, the command:
safe_finger @nasty.badguy.com
is run, and the results are piped into a mail message sent to the root user with the subject line:
in.tftpd->nasty.bad-guy.com
safe_finger is a command provided along with the TCP_wrappers that strips out any “bad” characters, like control sequences and data overruns. Running safe_finger @hostname generates a list of everyone currently logged into that system. The strings %h and %d are called expansions, and tcpd replaces them with the corresponding text for the host name and daemon process, respectively. Other expansions include %a for the client Internet address and %u for the client user name.

Now, this isn't a perfect solution, since our cracker friend may have disabled his finger service or altered it to give false information; however, this example does show us the power of the TCP_wrappers program.

NEWS CONTENTS

Old News ;-)

Configuring and using tcpwrappers

Logging Denied Connections

The logging of attempted (and failed) logins is done using the syslog facility.

By examining /etc/syslog.conf, you'll see

# The authpriv log file should be restricted access; these
# messages shouldn't go to terminals or publically-readable
# files.
authpriv.*;remoteauth.*                         /var/log/secure.log
This line will cause tcpwrappers to log any attempted logins to /var/log/secure.log.

Another option, is to add a line as follows:

*.info                                                  /var/log/allmessages

This will log any and all notifications of actions on your system. You can then use one of the common log sifting programs to notify you of any unusual activity. This will be covered in a future article on Stepwise - Editor

Note that any time you make changes to syslog.conf, you'll need to notify the syslogd process by sending it a -HUP signal, as shown above with inetd.

It is also worth repeating that you should never use tabs in the /etc/syslog.conf file, only spaces.



Etc

Society

Groupthink : Two Party System as Polyarchy : Corruption of Regulators : Bureaucracies : Understanding Micromanagers and Control Freaks : Toxic Managers :   Harvard Mafia : Diplomatic Communication : Surviving a Bad Performance Review : Insufficient Retirement Funds as Immanent Problem of Neoliberal Regime : PseudoScience : Who Rules America : Neoliberalism  : The Iron Law of Oligarchy : Libertarian Philosophy

Quotes

War and Peace : Skeptical Finance : John Kenneth Galbraith :Talleyrand : Oscar Wilde : Otto Von Bismarck : Keynes : George Carlin : Skeptics : Propaganda  : SE quotes : Language Design and Programming Quotes : Random IT-related quotesSomerset Maugham : Marcus Aurelius : Kurt Vonnegut : Eric Hoffer : Winston Churchill : Napoleon Bonaparte : Ambrose BierceBernard Shaw : Mark Twain Quotes

Bulletin:

Vol 25, No.12 (December, 2013) Rational Fools vs. Efficient Crooks The efficient markets hypothesis : Political Skeptic Bulletin, 2013 : Unemployment Bulletin, 2010 :  Vol 23, No.10 (October, 2011) An observation about corporate security departments : Slightly Skeptical Euromaydan Chronicles, June 2014 : Greenspan legacy bulletin, 2008 : Vol 25, No.10 (October, 2013) Cryptolocker Trojan (Win32/Crilock.A) : Vol 25, No.08 (August, 2013) Cloud providers as intelligence collection hubs : Financial Humor Bulletin, 2010 : Inequality Bulletin, 2009 : Financial Humor Bulletin, 2008 : Copyleft Problems Bulletin, 2004 : Financial Humor Bulletin, 2011 : Energy Bulletin, 2010 : Malware Protection Bulletin, 2010 : Vol 26, No.1 (January, 2013) Object-Oriented Cult : Political Skeptic Bulletin, 2011 : Vol 23, No.11 (November, 2011) Softpanorama classification of sysadmin horror stories : Vol 25, No.05 (May, 2013) Corporate bullshit as a communication method  : Vol 25, No.06 (June, 2013) A Note on the Relationship of Brooks Law and Conway Law

History:

Fifty glorious years (1950-2000): the triumph of the US computer engineering : Donald Knuth : TAoCP and its Influence of Computer Science : Richard Stallman : Linus Torvalds  : Larry Wall  : John K. Ousterhout : CTSS : Multix OS Unix History : Unix shell history : VI editor : History of pipes concept : Solaris : MS DOSProgramming Languages History : PL/1 : Simula 67 : C : History of GCC developmentScripting Languages : Perl history   : OS History : Mail : DNS : SSH : CPU Instruction Sets : SPARC systems 1987-2006 : Norton Commander : Norton Utilities : Norton Ghost : Frontpage history : Malware Defense History : GNU Screen : OSS early history

Classic books:

The Peter Principle : Parkinson Law : 1984 : The Mythical Man-MonthHow to Solve It by George Polya : The Art of Computer Programming : The Elements of Programming Style : The Unix Hater’s Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite

Most popular humor pages:

Manifest of the Softpanorama IT Slacker Society : Ten Commandments of the IT Slackers Society : Computer Humor Collection : BSD Logo Story : The Cuckoo's Egg : IT Slang : C++ Humor : ARE YOU A BBS ADDICT? : The Perl Purity Test : Object oriented programmers of all nations : Financial Humor : Financial Humor Bulletin, 2008 : Financial Humor Bulletin, 2010 : The Most Comprehensive Collection of Editor-related Humor : Programming Language Humor : Goldman Sachs related humor : Greenspan humor : C Humor : Scripting Humor : Real Programmers Humor : Web Humor : GPL-related Humor : OFM Humor : Politically Incorrect Humor : IDS Humor : "Linux Sucks" Humor : Russian Musical Humor : Best Russian Programmer Humor : Microsoft plans to buy Catholic Church : Richard Stallman Related Humor : Admin Humor : Perl-related Humor : Linus Torvalds Related humor : PseudoScience Related Humor : Networking Humor : Shell Humor : Financial Humor Bulletin, 2011 : Financial Humor Bulletin, 2012 : Financial Humor Bulletin, 2013 : Java Humor : Software Engineering Humor : Sun Solaris Related Humor : Education Humor : IBM Humor : Assembler-related Humor : VIM Humor : Computer Viruses Humor : Bright tomorrow is rescheduled to a day after tomorrow : Classic Computer Humor

The Last but not Least Technology is dominated by two types of people: those who understand what they do not manage and those who manage what they do not understand ~Archibald Putt. Ph.D


Copyright © 1996-2020 by Softpanorama Society. www.softpanorama.org was initially created as a service to the (now defunct) UN Sustainable Development Networking Programme (SDNP) without any remuneration. This document is an industrial compilation designed and created exclusively for educational use and is distributed under the Softpanorama Content License. Original materials copyright belong to respective owners. Quotes are made for educational purposes only in compliance with the fair use doctrine.

FAIR USE NOTICE This site contains copyrighted material the use of which has not always been specifically authorized by the copyright owner. We are making such material available to advance understanding of computer science, IT technology, economic, scientific, and social issues. We believe this constitutes a 'fair use' of any such copyrighted material as provided by section 107 of the US Copyright Law according to which such material can be distributed without profit exclusively for research and educational purposes.

This is a Spartan WHYFF (We Help You For Free) site written by people for whom English is not a native language. Grammar and spelling errors should be expected. The site contain some broken links as it develops like a living tree...

You can use PayPal to to buy a cup of coffee for authors of this site

Disclaimer:

The statements, views and opinions presented on this web page are those of the author (or referenced source) and are not endorsed by, nor do they necessarily reflect, the opinions of the Softpanorama society. We do not warrant the correctness of the information provided or its fitness for any purpose. The site uses AdSense so you need to be aware of Google privacy policy. You you do not want to be tracked by Google please disable Javascript for this site. This site is perfectly usable without Javascript.

Last modified: March 12, 2019