CIT 470: Advanced Network and System Administration. Topics. Risk Management. Security

Transcription

1 CIT 470: Advanced Network and System Administration Security CIT 470: Advanced Network and System Administration Slide #1 Topics 1. Risk Management 2. Security Policies 3. OS Hardening 4. Authentication 5. PAM 6. Passwords 7. Incident Response CIT 470: Advanced Network and System Administration Slide #2 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 Slide #3 1

2 Assets 1. Login account. 2. Network bandwidth. 3. Disk space. 4. Data. 5. Reputation. CIT 470: Advanced Network and System Administration Slide #4 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 Slide #5 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 Slide #6 2

3 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 Slide #7 Vulnerabilities 1. Bad/default passwords. 2. Unused services with open ports. 3. Unpatched software vulnerabilities. 4. Transmitting confidential data in cleartext. 5. Open modems or wireless networks. 6. Physical access to critical systems. 7. Uneducated users. CIT 470: Advanced Network and System Administration Slide #8 Attack Trees CIT 470: Advanced Network and System Administration Slide #9 3

4 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 Slide #10 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 Slide #11 Security Policies User Level Policies Users must sign before receiving resources. 1. Acceptable Use Policy 2. Monitoring and Privacy Policy 3. Remote Access Policy Business Level Policies 1. Network Connectivity Policy 2. Log Retention Policy CIT 470: Advanced Network and System Administration Slide #12 4

5 OS Hardening 1. Secure the physical system. 2. Install only necessary software. 3. Keep security patches up to date. 4. Delete or disable unnecessary user accounts. 5. Use secure passwords. 6. Disable remote access except where necessary. 7. Use sudo instead of su. 8. Run publicly accessible services in a jail. 9. Check logs regularly. 10. Configure firewall on each host. 11. Run security scanner to check security. 12. Document security configuration. CIT 470: Advanced Network and System Administration Slide #13 Secure the physical system 1. Place servers in a physically secure location. 2. Physically secure the case. 3. Place ID tags on all hardware. 4. Password protect the BIOS. 5. Disable booting from removable media. CIT 470: Advanced Network and System Administration Slide #14 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 Slide #15 5

6 Security Patches Subscribe to vendor security patch list. Or know vendor s update schedule. MS Windows updates on 2 nd 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 Slide #16 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 Slide #17 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 Slide #18 6

7 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 Slide #19 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 Slide #20 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 Slide #21 7

8 Authentication Binding of an identity to a subject Based on: 1. What the entity knows (e.g., passwords) 2. What the entity has (e.g., access card) 3. What the entity is (e.g., fingerprints) 4. Where the entity is (e.g., local terminal) Two-factor authentication CIT 470: Advanced Network and System Administration Slide #22 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 Slide #23 Group Access Control Matrix De v RE Fin Re s Developers W R R Release Engineers R W R Finance W R Human Resources R W Operations R R W HR Ops Infra Se c System Administration A A A A A A A Security A A A A A A A A Dev = developer, RE = release engineering, Fin = finance, Res = corporate resource (intranet), HR = human resources, Ops = operat Inf = infrastructure (mail/auth servers, etc.), Sec=security (firewalls, IDS) A = administrative access, R = read, W = write CIT 470: Advanced Network and System Administration Slide #24 8

9 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 Slide #25 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 Slide #26 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 Slide #27 9

10 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 Slide #28 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 Slide #29 Biometrics Identify by physical chars Fingerprint Iris scan Unique identifiers. Not secrets. Can t be changed at will. Possible outcomes: 1. Correct person accepted 2. Imposter rejected 3. Correct person rejected (False Rejection) 4. Imposter accepted (False Acceptance) A tradeoff always exists between false acceptances and false rejections. CIT 470: Advanced Network and System Administration Slide #30 10

11 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 Slide #31 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 Slide #32 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 Slide #33 11

12 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 Slide #34 Incident Response Goals 1. Determine if a security breach occurred. 2. Contain intrusion to prevent further damage. 3. Recover systems and data. 4. Prevent future intrusions of same kind. 5. Investigate and/or prosecute intrusion. 6. Prevent public knowledge of incident. CIT 470: Advanced Network and System Administration Slide #35 Incident Response Phases to restore system to site security policy: 1. Preparation for attack (before attack detected) 2. Identification of attack 3. Containment of attack (confinement) 4. Damage assessment 5. Preserve evidence (if necessary) 6. Eradication of attack (stop attack) 7. Recovery from attack (restore system to secure state) 8. Follow-up to attack (analysis and other actions) CIT 470: Advanced Network and System Administration Slide #36 12

13 References 1. Michael D. Bauer, Linux Server Security, 2 nd edition, O Reilly, Aeleen Frisch, Essential System Administration, 3 rd edition, O Reilly, Simson Garfinkel, Gene Spafford, and Alan Schartz, Practical UNIX and Internet Security, 3 rd edition, O Reilly & Associates, Andrew Morgan, Linux PAM System Administrator s Guide, Evi Nemeth et al, UNIX System Administration Handbook, 3 rd edition, Prentice Hall, RedHat, Red Hat Enterprise Linux 4 Reference Guide, Manual/ref-guide/, CIT 470: Advanced Network and System Administration Slide #37 13