1. CIT 470: Advanced Network and System Administration
Security
CIT 470: Advanced Network and System Administration

2. CIT 470: Advanced Network and System Administration
Topics
Risk Management
Security Policies
OS Hardening
Authentication
PAM
Passwords
Incident Response
CIT 470: Advanced Network and System Administration

3. CIT 470: Advanced Network and System Administration
Risk Management
Risk is the relationship between your assets, the vulnerabilities characteristic to those assets, and attackers who wish to access or modify those assets.
CIT 470: Advanced Network and System Administration

4. CIT 470: Advanced Network and System Administration
Assets
Login account.
Network bandwidth.
Disk space.
Data.
Reputation.
CIT 470: Advanced Network and System Administration

5. CIT 470: Advanced Network and System Administration
Security Goals
Data confidentiality
Customer account data (credit cards, identity)
Trade secrets
Administrative data (passwords, configuration)
Data integrity
Administrative data
Software downloads (patches, free tools)
Web pages
CIT 470: Advanced Network and System Administration

6. CIT 470: Advanced Network and System Administration
Security Goals
System integrity
System binaries
Kernel
System/network availability
Network bandwidth
Network services (auth, file, mail, print)
Disk space
CIT 470: Advanced Network and System Administration

7. CIT 470: Advanced Network and System Administration
Threats
Financial motives
Identity theft
Phishing
Spam
Extortion
Botnets
Political motives
Danish sites hacked after Mohammed cartoons.
Personal motives
Just for fun.
Insider revenge.
CIT 470: Advanced Network and System Administration

8. CIT 470: Advanced Network and System Administration
Vulnerabilities
Bad/default passwords.
Unused services with open ports.
Unpatched software vulnerabilities.
Transmitting confidential data in cleartext.
Open modems or wireless networks.
Physical access to critical systems.
Uneducated users.
CIT 470: Advanced Network and System Administration

9. CIT 470: Advanced Network and System Administration
Attack Trees
CIT 470: Advanced Network and System Administration

10. CIT 470: Advanced Network and System Administration
Defense Types
Perimeter Security
Firewall off network to prevent intrusions.
What about wireless?
What about mobile computing?
Defense in Depth
Secure systems at all levels:
Network perimeter (firewall)
Intrusion detection
System hardening
CIT 470: Advanced Network and System Administration

11. CIT 470: Advanced Network and System Administration
Defenses
Vulnerability mitigation
Use secure authentication systems.
Deploy software in secure configuration.
Patch security flaws quickly.
Attack mitigation
Firewalls to prevent network attacks.
IDS to detect attacks.
Virus/spyware scanners.
CIT 470: Advanced Network and System Administration

12. CIT 470: Advanced Network and System Administration
Security Policies
User Level Policies
Users must sign before receiving resources.
Acceptable Use Policy
Monitoring and Privacy Policy
Remote Access Policy
Business Level Policies
Network Connectivity Policy
Log Retention Policy
CIT 470: Advanced Network and System Administration

13. CIT 470: Advanced Network and System Administration
OS Hardening
Secure the physical system.
Install only necessary software.
Keep security patches up to date.
Delete or disable unnecessary user accounts.
Use secure passwords.
Disable remote access except where necessary.
Use sudo instead of su.
Run publicly accessible services in a jail.
Check logs regularly.
Configure firewall on each host.
Run security scanner to check security.
Document security configuration.
CIT 470: Advanced Network and System Administration

14. Secure the physical system
Place servers in a physically secure location.
Physically secure the case.
Place ID tags on all hardware.
Password protect the BIOS.
Disable booting from removable media.
CIT 470: Advanced Network and System Administration

15. Install only Necessary Software
Put different services on different hosts.
A compromise in ftp shouldn’t compromise mail.
Improves reliability and maintainability too.
Common unnecessary packages
X-Windows
Software development (gcc, gdb, etc.)
CIT 470: Advanced Network and System Administration

16. CIT 470: Advanced Network and System Administration
Security Patches
Subscribe to vendor security patch list.
Or know vendor’s update schedule.
MS Windows updates on 2nd Tuesday.
Update test host first.
yum update
Patches can sometimes break services.
Update other hosts after that.
May need to schedule downtown if reboot required.
CIT 470: Advanced Network and System Administration

17. CIT 470: Advanced Network and System Administration
Jails
Complete isolation: virtual machines.
Partial isolation: chroot
chroot /var/httpd httpd
chroot filesystem needs:
/var/httpd/etc: limited /etc/{passwd,shadow,group}
/var/httpd/usr/lib shared libraries
/var/httpd/bin: extra binaries
/var/httpd/var/log: log space
/var/httpd/tmp: temporary space
CIT 470: Advanced Network and System Administration

18. CIT 470: Advanced Network and System Administration
Check Logs
Review logs every morning.
Better yet, have a program scan them.
logwatch
swatch
Send logs to a central server for
security: attacker can’t hide tracks by deleting
ease of use: you can read all logs in one place
CIT 470: Advanced Network and System Administration

19. CIT 470: Advanced Network and System Administration
Security Scanning
Scan host security
Run bastille on host.
Scan network security
Scan for open ports with nmap.
Scan for vulnerabilities with nessus.
CIT 470: Advanced Network and System Administration

20. CIT 470: Advanced Network and System Administration
Intrusion Detection
Host-based intrusion detection
Check if system files are modified.
Check for config / process modifications.
Tools: tripwrite, osiris, samhain
Network-based intrusion detection
NIDS = Sniffer + traffic analysis + alert system.
Check for suspicious activities: port scans, etc.
Check for attack signatures: worms, etc.
Tools: snort, p0f
CIT 470: Advanced Network and System Administration

21. CIT 470: Advanced Network and System Administration
Security Auditing
Internal and External Audits
Internal: by a group within organization.
External: by a group external to organization.
Audit areas
Check compliance with security policy.
Check physical security of building, data center.
Check that machines have up to date patches.
Scan networks to verify hosts + services.
Penetration testing.
CIT 470: Advanced Network and System Administration

22. CIT 470: Advanced Network and System Administration
Authentication
Binding of an identity to a subject
Based on:
What the entity knows (e.g., passwords)
What the entity has (e.g., access card)
What the entity is (e.g., fingerprints)
Where the entity is (e.g., local terminal)
Two-factor authentication
CIT 470: Advanced Network and System Administration

23. Purpose of Authentication
Access Control
Most systems base access rights on identity of principal executing the process.
Accountability
Logging and auditing functions.
Need to track identity across account/role changes (e.g., su, sudo).
CIT 470: Advanced Network and System Administration

24. CIT 470: Advanced Network and System Administration
Access Control Matrix
Group
Dev RE
Fin
Res HR
Ops
Infra
Sec
Developers W R
Release Engineers
Finance
Human Resources
Operations
System Administration A
Security
Dev = developer, RE = release engineering, Fin = finance,
Res = corporate resource (intranet), HR = human resources, Ops = operations,
Inf = infrastructure (mail/auth servers, etc.), Sec=security (firewalls, IDS)
A = administrative access, R = read, W = write
CIT 470: Advanced Network and System Administration

25. CIT 470: Advanced Network and System Administration
Single-sign on
Login once to access all computing resources
UNIX
Windows
Web Applications
Databases
Remote access
Difficult to achieve in practice.
Kerberos (Active Directory)
CIT 470: Advanced Network and System Administration

26. CIT 470: Advanced Network and System Administration
Use Secure Passwords
Attacks against Passwords
Password sniffing
Password guessing via login
Password cracking
Defences
Do not transfer passwords over the network.
Secure /etc/{passwd,shadow}
Configure password quality/aging rules.
Test your passwords by cracking them.
CIT 470: Advanced Network and System Administration

27. CIT 470: Advanced Network and System Administration
Password Quality
Use pam_cracklib.so in system-auth
Options
retry=#: Maximum # of retries.
minlen=#: Minimum password length.
lcredit=#: Min # of lower case letters.
ucredit=#: Min # of upper case letters.
dcredit=#: Min # of digits.
ocredit=#: Min # of other chars.
CIT 470: Advanced Network and System Administration

28. CIT 470: Advanced Network and System Administration
Password Aging
Configure /etc/login.defs before creating accounts.
PASS_MAX_DAYS: Max # of days before password expires.
PASS_MIN_DAYS: Min # of days before user can change pw.
PASS_WARN_AGE: # of days for pw change notice given.
Also configure /etc/default/useradd
INACTIVE: # of days after pw expiration that account is disabled.
EXPIRE: Account expiration date in format YYYY-MM-DD.
Remember old passwords with pam_unix.so
Prevents users from changing password back to old value.
Modify /etc/pam.d/system-auth
Set pam_unix.so option remember=26
Create /etc/security/opasswd to store old passwords.
CIT 470: Advanced Network and System Administration

29. CIT 470: Advanced Network and System Administration
One-Time Passwords
A password that’s invalidated once used.
Challenge: number of auth attempt
Response: one-time password
Problems
Generation of one-time passwords
Use hash or crytographic function
Synchronization of the user and the system
Number or timestamp passwords
CIT 470: Advanced Network and System Administration

30. CIT 470: Advanced Network and System Administration
Biometrics
Identify by physical chars
Fingerprint
Iris scan
Unique identifiers.
Not secrets.
Can’t be changed at will.
Possible outcomes:
Correct person accepted
Imposter rejected
Correct person rejected (False Rejection)
Imposter accepted (False Acceptance)
A tradeoff always exists
between false acceptances
and false rejections.
CIT 470: Advanced Network and System Administration

31. Disable Unnecessary Accounts
/etc/passwd contains application accounts.
Delete unnecessary application accounts.
ex: uucp, games, gdm, xfs, rpcuser, rpc
All should have locked passwords.
Set shell to /bin/noshell or /bin/false.
Disable user accounts immediately on termination of employment.
CIT 470: Advanced Network and System Administration

32. Disabling Remote Access
Disable cleartext protocols
telnet, ftp, rsh, rlogin
Disable root access via ssh.
Set PermitRootLogin to “no” in sshd_config
Remove root non-terminal consoles
Set in /etc/securetty
Disable password access via ssh
Use keys instead.
CIT 470: Advanced Network and System Administration

33. CIT 470: Advanced Network and System Administration
sudo
Login as root only for single-user mode.
Use sudo instead of su.
sudo command
Advantages:
Uses user password instead of root’s password.
Logs who executed what commands as root.
Can delegate limited powers to some users.
CIT 470: Advanced Network and System Administration

34. CIT 470: Advanced Network and System Administration
What is an Incident?
Violation of security policy:
Unauthorized access of information
Unauthorized access to machines
Embezzlement
Virus or worm attack
Denial of service attacks
spam or harassment
CIT 470: Advanced Network and System Administration

35. Incident Response Goals
Determine if a security breach occurred.
Contain intrusion to prevent further damage.
Recover systems and data.
Prevent future intrusions of same kind.
Investigate and/or prosecute intrusion.
Prevent public knowledge of incident.
CIT 470: Advanced Network and System Administration

36. CIT 470: Advanced Network and System Administration
Incident Response
Phases to restore system to site security policy:
Preparation for attack (before attack detected)
Identification of attack
Containment of attack (confinement)
Damage assessment
Preserve evidence (if necessary)
Eradication of attack (stop attack)
Recovery from attack (restore system to secure state)
Follow-up to attack (analysis and other actions)
CIT 470: Advanced Network and System Administration

37. CIT 470: Advanced Network and System Administration
References
Michael D. Bauer, Linux Server Security, 2nd edition, O’Reilly, 2005.
Aeleen Frisch, Essential System Administration, 3rd edition, O’Reilly, 2002.
Simson Garfinkel, Gene Spafford, and Alan Schartz, Practical UNIX and Internet Security, 3rd edition, O’Reilly & Associates, 2003.
Andrew Morgan, Linux PAM System Administrator’s Guide,
Evi Nemeth et al, UNIX System Administration Handbook, 3rd edition, Prentice Hall, 2001.
RedHat, Red Hat Enterprise Linux 4 Reference Guide,
CIT 470: Advanced Network and System Administration