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The less the number of accounts the less chances that something will going on undetected. That means that it make sense to delete redundant accounts and groups.
At the same time please be aware that there is a lot of stupid security advice about account security on the Web. Be selective and understand what are you doing. Excessive zeal can lead to making user life more difficult that it should and prompt them for finding workarounds. And usually that are very inventive in this activity...
Also for existing account there should be a set of rules as for permissions and scripts running to verify that those rules are followed. One useful precaution is to remove SUID privileges from the filesystem that holds /home directory.
The same is applicable to /tmp.
See some useful (although outdated) recommendations can be found in Practical UNIX & Internet Security, 2nd Edition Appendix A
Chapter 8: Defending Your Accounts
Unix System Security Checklist
The following is a partial checklist of actions that can be taken to improve security of your Unix system. This list is neither complete, nor can all of the steps be taken on a given system.
It is not sufficient to just go through this list once, as many of these things will change over time. You should periodically "audit" your network, or install tools that will automatically monitor some aspects of system security and notify you of anything that is discovered. Even then, there is still the potential for successful attacks (through modems or any network or terminal connections). You should never consider your systems 99.999% safe unless there is no way to get in besides the keyboard at the console (to be 100% safe, you must also remove the power supply!)
- Account Security
- Inform users of "good" password selection criteria, and use either a pro-active password checker or a password cracking program to verify that passwords are secure (e.g., ftp://sable.ox.ac.uk/pub/comp/security/software/crackers/)
- If desired, and your system supports it, implement a password generator which generates "good" passwords (avoid being too clear about how the program works, since this simplifies writing attack programs)
- If desired, and your system supports it, implement password aging
- If your system supports it, implement a shadow password file (e.g., Shadow from ftp://ftp.cs.widener.edu/pub/src/adm/)
- Place expiration dates on, and periodically "expire", all accounts to eliminate unused accounts
- Carefully restrict guest accounts, using restricted shells if possible
- Do not leave "idle" (i.e. unused) guest accounts enabled
- Password protect all well-known accounts that must be on the system; delete well-known accounts that are not needed
- Make sure all accounts have passwords or "*" in the password field
- Eliminate group and shared accounts, replacing them with groups instead
- Avoid placing the current directory (".") in your (especially root's) search path
- Make sure default file protections for newly created files do not allow group/world read/write access by using a "umask" value of 022, 027, or 077, especially on the root account
- Codify rules and policies for operating as the "super user"; use "su -" instead of logging in as root to monitor use of the root account--then monitor the log files to see when this account is used
- Write-protect the "root" account's startup files and home directory
- Disable message permission using the mesg command if you are using a terminal with block-mode transmission features or remotely programmable function keys
- Minimize the number of accounts on servers and "critical" hosts
- Minimize the number of users with "super user" privileges
- Check account security with a tool like COPS or Tiger
Unix security - Wikipedia, the free encyclopedia
Chapter 3 Computer System Security and Access Controls
Web Security, Privacy & Commerce, 2nd Edition Chapter 8 The Web's War on Your Privacy
You should also visit the CERT web site. There you will find :
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
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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
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 DOS : Programming Languages History : PL/1 : Simula 67 : C : History of GCC development : Scripting 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
The Peter Principle : Parkinson Law : 1984 : The Mythical Man-Month : How to Solve It by George Polya : The Art of Computer Programming : The Elements of Programming Style : The Unix Haterís Handbook : The Jargon file : The True Believer : Programming Pearls : The Good Soldier Svejk : The Power Elite
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