Silberschatz, Galvin and Gagne 2002 19.1 Operating System Concepts The Security Problem A system is secure iff its resources are used and accessed as.
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Silberschatz, Galvin and Gagne 2002 19.1 Operating System Concepts The Security Problem A system is secure iff its resources are used and accessed as intended under all circumstances Security must consider the external environment of the system, and protect it from: unauthorized access. malicious modification or destruction accidental introduction of inconsistency. Easier to protect against accidental than malicious misuse. Four levels of control Physical Human Network OS Hardware support for protection (internal) needed for security in the OS
Silberschatz, Galvin and Gagne 2002 19.2 Operating System Concepts Authentication Control access to resources by login User identity most often established through passwords Login and lower level access Basic mechanism of matching encrypted strings Passwords must be kept secret. Frequent change of passwords. Use of “non-guessable” passwords. Log all invalid access attempts.
Silberschatz, Galvin and Gagne 2002 19.3 Operating System Concepts Authentication Attacks User information (cat’s name) Brute force (try them all) Surveillance (shoulder surfing) Dummy logins (trojan horse) Sniffing (telnet) Offsite passwd file attacks Alternatives Password passing (system generated) Passcards (physical control) Biometrics (retina images) Signature (False negatives) Algorithms (Little danger if response is exposed) Challenges Onetime passwords Password generators (timed smartcards) Books of passwords
Silberschatz, Galvin and Gagne 2002 19.4 Operating System Concepts Program Threats Trojan Horse Exploits mechanisms for allowing programs written by users to be executed by other users, e.g., login, editor, passwd, ls Search paths as a way to invoke Trap Door Specific user identifier or password that circumvents normal security procedures. Could be included in a compiler. Stack and Buffer Overflow Exploits a bug in a program (overflow either the stack or memory buffers.)
Silberschatz, Galvin and Gagne 2002 19.5 Operating System Concepts System Threats Worms Standalone program Use spawn mechanism Internet worm Exploited UNIX networking features (remote access), and stack overflow in finger and debug features in sendmail. Grappling hook program uploaded main worm program.
Silberschatz, Galvin and Gagne 2002 19.6 Operating System Concepts System Threats Viruses – fragment of code embedded in a legitimate program. Mainly affect microcomputer systems. Downloading viral programs from public bulletin boards or exchanging floppy disks containing an infection. Macro viruses Safe computing, e.g., RTF Denial of Service Overload the targeted computer preventing it from doing any useful work. Change boot device
Silberschatz, Galvin and Gagne 2002 19.7 Operating System Concepts Threat Monitoring Check for suspicious patterns of activity Several incorrect password attempts may signal password guessing - limit attempts Cage rattlers - limit attempts from an IP address Unexpected long-running processes Rejected file accesses Audit log – records the time, user, and type of all accesses to an object; useful for recovery from a violation and developing better security measures.
Silberschatz, Galvin and Gagne 2002 19.8 Operating System Concepts Threat Monitoring (Cont.) Scan the system periodically for security holes; done when the computer is relatively unused. Short or easy-to-guess passwords Unauthorized set-uid programs Unauthorized programs in system directories Improper directory protections Improper protections on system data files Dangerous entries in the program search path (Trojan horse) Changes to system programs: monitor checksum values
Silberschatz, Galvin and Gagne 2002 19.9 Operating System Concepts Firewalls A firewall is placed between trusted and untrusted hosts. The firewall limits network access between these two security domains.