Transcript Operating System Security

Operating system Security
By
Murtaza K. Madraswala
Protection
Control access by limiting file types accessed by different
users
Only authorized processes can operate on memory
segments, CPU and other resources
Security
• Protect information integrity by ensuring
authentication of system users
• Prevent unauthorized access
• Prevent malicious destruction of data
• Prevent accidental introduction of inconsistency
Security vs. Protection
Security takes into consideration the protection
system which is strictly internal, as well as the
external environment in which the system
operates
Security violations can be malicious or
accidental
Security (Contd.)
Malicious violations
•
•
•
•
Unauthorized reading of data
Unauthorized writing of data
Unauthorized destruction of data
Preventing legitimate system use (Denial of service)
Security (Contd.)
Four levels of security measures
1.
2.
3.
4.
Physical – Physical protection of the computer system
Human – Screening of users given access to the
computer system
Network
Operating System – OS must be capable of protecting
itself from accidental or intentional security breaches
Operating System Security
User authentication
Based on
- User possession (of key or card)
- User knowledge (user identifier + password)
- User attribute (fingerprint, retina pattern,
signature)
Passwords
• Password vulnerabilities
• Encrypted passwords
• One-Time passwords
Biometrics
Program Threats
A program written by one user and used by another may
cause unexpected behavior
Trojan horse –
This problem is created by the operating system which
allows the programs written by one user to be executed
by another
This is a code segment that can misuse it environment
Program Threats (contd.)
Trap door
Stack and buffer overflow
System threats
Most operating systems allow processes to
spawn other processes. This creates situations
in which operating system resources and files
are misused
System threats (Contd.)
Worms
Worms are programs that reduce system performance
by spawning copies of themselves repeatedly, locking
out system use by all other processes. In a network
worms may reproduce across systems and bring down
the entire network
System threats (Contd.)
Viruses
A virus is a fragment of code embedded in a
legitimate program. It is capable of
modifying/destroying files, causing program
malfunctions and system crashes.
System threats (Contd.)
Denial of Service
The focus of this attack is to disable the
legitimate use of a system/facility rather than
gaining information or stealing resources
Intrusion detection
Strives to detect attempted or successful intrusions
into a computer system, and initiate a proper
response.
Two approaches:
1. Signature-based detection – Here system input or
traffic is examined for specific behavior patterns
2. Anomaly detection – This approach attempts to detect
anomalous behavior within the computer system.
Intrusion detection (Contd.)
• Signature-based detection attempts to characterize
dangerous behavior and detects when such behavior
occurs
• Anomaly detection attempts to characterize normal
behaviors and detects when something abnormal occurs
Intrusion detection (Contd.)
Auditing and logging
In audit-trail processing, security relevant events are
logged to an audit trail and matched against attack
signatures (signature-based detection) or analyzed for
anomalous behavior (anomaly detection)
Intrusion detection (Contd.)
System-Call Monitoring
Process system calls are monitored to detect instances
when a process deviates from the expected system-call
behavior
Attacks that attempt to take over a process by exploiting
the buffer-overflow vulnerability, and execute the
attacker’s code rather than the original code can be
detected using this technique
References
• Silberschatz, Galvin & Gagne, Operating System
Concepts (6 ed.), John Wiley and Sons
• R. Summers, Secure Computing – Threats and
Safeguards, McGraw-Hill
• M. Milenkovic, Operating Systems – Concepts and
Designs, McGraw-Hill
• W. Stallings, Operating Systems – Internals and Design
Principles, Prentice Hall