CSCD 434 Network Security Spring 2014 Lecture 1 Course Overview.
CSCD 303 Essential Computer Security Winter 2014 Lecture 7 - Desktop Security Vulnerabilities...
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Transcript of CSCD 303 Essential Computer Security Winter 2014 Lecture 7 - Desktop Security Vulnerabilities...
CSCD 303Essential Computer SecurityWinter 2014
Lecture 7 -
Desktop Security VulnerabilitiesReading: References at end of Slides
Security Hole
Overview
• Learning Objectives• Introduce OS Vulnerabilities
• What are they• Why do they happen
• Study Access Control Vulnerabilities
• Users - Passwords
Security and Vulnerabilities• According to Merriam-Webster, Vulnerable
Defined Vulnerable means “exposed to possibility of being attacked
or harmed, either physically or emotionally: ‘we were in a vulnerable position’.”
• Computer Security, Vulnerability Defined Security Vulnerability refers to system flaw that can leave it open to attack
A vulnerability may also refer to any type of weakness in a
1. Computer system itself, 2. Set of procedures, or 3. Anything that leaves information security exposed
to a threat
OS Vulnerabilities
• What are some vulnerabilities common to all OS's?
OS Vulnerabilities
Look Common OS Vulnerabilities1. Buffer Overflow
2. Unvalidated input
3. Race conditions
4. Access-control problems
5. Weaknesses in authentication
Buffer Overflow
• Every program that allows input–Needs to store input in memory until it can use for its intended purpose
– Examples: Web form, enter your name Saving a file, enter file name, Search engine, enter search string
What is the definition of a buffer?
Buffer Defined
A temporary storage area, usually in RAM Purpose of most buffers is to act as holding
area, enabling CPU to manipulate data before transferring it to a device
Because processes of reading and writing data to a disk are relatively slow, many programs keep track of data changes in a buffer and then copy the buffer to a disk
For example, word processors employ a buffer to keep track of changes to files
Buffer overflow
• Program should check user input to make sure its correct length – Frequently programmer does not bother to check
length of input Programmer assumes user will not do anything unreasonable– Language allows him/her to overwrite buffer– For example
• Form asks you to enter your first name Has room for 12 characters First Name
• User's first name is really long, 15 characters Francessca-Ally F r a n c e s s c a - A lly
Overflow Chars
Buffer Overflows
• How are buffer overflows used to compromise your computer?– As part of long data input, attacker will
include some of his own code– Then, manipulates flow of program in memory
to execute his code ...more on this later– If program that is overflowing is running with
administrator privileges, attacker code has administrator privileges– Then, they can do anything to your
computer !!!
Microsoft Vulnerabilities
• Does anyone know about the vulnerability described in
Microsoft Security Bulletin MS08-067 ?
Buffer Overflow MS08-067
• Buffer overflow vulnerability in Windows Server Service– For systems running Windows 2000, XP, Windows
7 and Server 2003, remote, unauthenticated attacker could exploit this vulnerability• In Vista, attacker would need to be authenticated
– Since Server service runs with Administrator privileges, an attacker could take complete control of a vulnerable system– This IS the vulnerability that Conficker exploited!
Details of MS08-067• Specifically, this vulnerability is a buffer overflow
in an unauthenticated Windows SMB file sharing session
– SMB = Server Message Block, protocol for sharing server resources like files and printers
• Malicious client can bind to service and issue a request with an overly long argument
– Overflowing a buffer and possibly executing arbitrary code on the vulnerable server
• This is one way malware is getting onto systems
http://asert.arbornetworks.com/2008/10/ms08-067-server-service-vulnerabilities-redux-and-wormability/
What is the Server Message Block? Operates as an application-layer network
protocol Provides shared access to files, printers,
serial ports, and miscellaneous communications between nodes on a network
Also provides an authenticated inter-process communication mechanism
Linux Buffer Overflow Vulnerabilities Is Linux or Mac OS X immune to buffer overflows?
No. They have these too … Google search of “buffer overflow vulnerabilities
in linux 2013” Came back with 286,000 hits Among the problems
Stack based X-Windows vulnerability Affects all linux distributions
Adobe flash player – Linux Re-ran the search “buffer overflow vulnerabilities
in linux kernel 2013” Came back with 74,000 hits
Unvalidated Input Attacks
• Any input received by a program from an untrusted source is a potential target for attack– Hackers look at every source of input– Try to inject their own code or script to be
run by the system accepting the input– May allow them unauthorized access
Validating Input Input needs to meet programmer expectations For whatever input required:
• HTML, email, userid or valid database request Compare input to what is known to be acceptable Commonly use regular expressions, which are patterns of characters describe allowable input Bad input is either rejected or altered
Race Condition• A race condition exists when two events can occur
out of sequence … unexpected– If correct sequence is required for proper functioning
of program, potential vulnerability can be exploited– If attacker can cause correct sequence not to
happen and insert malicious code, change a filename, or otherwise interfere with normal operation
– Race condition is a security vulnerability• Attackers can sometimes take advantage of small time
gaps in processing of code– Interfere with sequence of operations– Which they then exploit
Race Conditions
• There are two basic types of race condition that can be exploited1. Time of check/time of use2. Interprocess communication
Race Condition: Time of Check/Time of Use• Application checks some condition before
undertaking an action• For example, it might check to see if file exists
before writing to it• Attacker, by continuously running program that
creates new temporary file can create file in gap between when application checked to make sure temporary file didn't exist and when it opens it for writing• Application then opens attacker's file and writes
to it ... • System routine opens an existing file if there is
one, and creates a new file only if there is no existing file
Race Condition:Interprocess Communication• Separate processes—either within a single
program or in two different programs—sometimes have to share information– For example, if two processes share same
data, potential attacker to alter data after one process sets it but before other reads it– Solution to race conditions of this type is
to use some locking mechanism to prevent one process from changing a variable until another is finished with it
Access Control
• Many OS security vulnerabilities are created by careless or improper use of access controls, or by failure to use them at all– Exploits involve an attacker somehow
gaining more privileges than they should have• Privileges, also called permissions, are
access rights granted by the operating system• Controls who is allowed to read and write
files, see directories, execute a program
Access ControlsOperating Systems Access controls provided with an operating
system typically authenticate users using some mechanism such as passwords or Kerberos, then mediate their access to files, communications ports, and other system resources
Their effect can often be modelled by a matrix of access permissions, with columns for files and rows for users.
Following Example ... We’ll write r for permission to read, w for
permission to write, x for permission to execute a program, and (–) for no access at all
Access ControlsOperating Systems Alice, the manager, needs to execute the operating
system and application, she mustn’t have the ability to tamper with them, She also needs to read and write the data.
Bob, the auditor, can read everything, and execute OS
Sam, the Accountant needs read, write and execute OS, Prog
Access ControlOperating Systems Individual and Group Access Control
So far, talked about individual Access Control
Group Access Control is another level of security
Typical to have several groups Users vs Administrators Could also be distinctive
roles Accountants Managers Sales Staff
Access Control Lists
Groups Implemented via Access Control Lists
Formally, can specify individual and group access with Access Control Lists
Store ownership and access along with resource
Example – Accounting DataSam and Alice can read and write – rwBob can only read - r
Access Control• Of particular interest to attackers is
gaining of root or administrator privileges– Unrestricted permission to perform any
operation on system• Application running with root privileges can
access everything and change anything–Many security vulnerabilities involve
programming errors that allow an attacker to obtain root privileges– Some involve taking advantage of buffer
overflows or race conditions ...
Authentication and Authorization• Access control enforced by applications,
requires users to authenticate before granting authorization to perform an operation
• Authentication can involve requesting a users credentials
1. User name and password
2. Digital certificates
3. Biometrics – Fingerprints, Iris/retina scan
4. Dynamic biometrics – signature, voice recognition
Authentication as Security Mechanism What is authentication?
Authentication is the process of determining whether someone or something is, in fact, who or what it is declared to be
How do we do this in the real world?
Digital Authentication
How do computers use authentication ?
Grant access to resources Typically, information, but also
access to hardware, printers, other systems
Also, access to being able to run certain programs
Users as Vulnerabilities
• Often weakest link in chain of security features protecting a user's data and software is the user himself
• Attackers increasingly concentrate on fooling users into executing malicious code, handing over passwords, credit-card numbers, and other private information
–Default Passwords, no passwords or weak passwords contribute to users as vulnerabilities
Passwordsas Authentication Mechanisms
Users and Passwords
• Fortunately or unfortunately ...• Users must be entrusted with security
of their own systems– Passwords still used extensively as way
to authenticate people–Why are they still used?– Easy to use, know how to use them,
people are familiar with them, cheap!!– Can be used both locally and remotely• On your home PC and over the Internet
Passwords
• While we may find them annoying, and even take them for granted, • Important to remember why
passwords are important– Passwords are often first and possibly
only defense against intrusion
Password Weaknesses
• If password is sent in clear, can be intercepted
• Password is encrypted, requires establishment of encryption key Where is key stored, can key be compromised?
• People choose bad passwords• Passwords are easily observed• Passwords can be sniffed by spyware
People Give away Passwords
http://news.bbc.co.uk/2/hi/technology/3639679.stm
• Security crumbles in the face of sweet bribes
• More than 70% of people would reveal their computer password in exchange for a bar of chocolate, according to a survey
• It also showed that 34% of respondents volunteered their password when asked without even needing to be bribed
Disadvantages ofPasswords
Note: Passwords are generally pretty
weak
• University of Michigan: 5% of passwords were goblue
• Passwords often used in more than one place
Disadvantages of Passwords
Attacker can access the hashed password
– Can guess and test passwords offline
“password cracking”
Lots of help– John the Ripper– Cain and Able – THC Hydra
• You will get to see how easy it is to use Cain and Able
How to Break Passwords
• Three main ways programs “crack” passwords1. Dictionary attack - tries thousands of words
from dictionary files as possible passwords– Every word from dictionary is tested in a
variety of modifications, cat – tac, cat1, cated– Encrypt words from list of English words,
compare each encryption against stored encrypted version of users' passwords
How to Break Passwords
2. Brute Force Attack• Finds passwords by checking all possible
combinations of characters from the Symbol Set– You can make a big Brute-Force-
Dictionary to implement Brute-Force attack– Actually, don't have to … these come
with automated tools !!!
How to Break Passwords
3. Guessing Attack – Guess based on something “known”– blank (none)– words "password", "passcode", "admin" and their
derivatives– a row of letters from the qwerty keyboard -- qwerty itself,
asdf, or uiop– user's name or login name– name of their significant other, a friend, relative or pet– birthplace or date of birth, or a friend's, or a relative's– automobile license plate number, or a friend's, or a
relative's– office number, residence number or most commonly, their
mobile number
Effectiveness of Password Guessing
How well do these work?Guessing ... • September 2008, Yahoo e-mail account of
Governor of Alaska and Vice President of the United States nominee Sarah Palin
• Accessed without authorization by someone who researched answers to two of her security questions– Zip code and date of birth and was able to
guess the third, where she met her husband!
Twitter Hacker Succeeded with Self-authored Tool Weak Password Brings ‘Happiness’
to Twitter Hacker An 18-year-old hacker with a history of
celebrity pranks has admitted to hijacking of multiple high-profile Twitter accounts, including President-Elect Barack Obama’s, and the official feed for Fox News – 2009
http://www.wired.com/threatlevel/2009/01/professed-twitt/
Effectiveness Password Guessing
• Another Example–Gary McKinnon, accused of perpetrating
"biggest military computer hack of all time",– Claimed that he was able to get into
military's networks by using Perl script that searched for blank passwords–His report suggests that there were
computers on these networks with no passwords at all!
Effectiveness of Password Cracking
Penn state CS Engineering Department• Ran John the Ripper on CSE authentications – 3500 in all
• In first hour, 25% were recovered – About half of these due to dictionary attacks – But, half using other heuristics and brute force
• Over 5 days, 35% were recovered – Steady state recovery due to brute force
Top Password cracking software listed here
http://sectools.org/crackers.html
Password Cracking Stats
Common Password Advice
Should be at least 8 charactersUse characters from each of the following four
classes: • English upper case letters • English lower case letters • Arabic numerals (0,1,2,…) • Non-alphanumeric (special) characters such as
punctuation symbolsDon’t use a proper name or any word in dictionary
without misspelling it in some wayDon’t reuse password you have used beforeDon’t use the same password for different types
of systems
Cat or Dog – BadQvmerx49z! - Good
How Passwords are Used• Windows Files On Windows systems password hashes are stored in the SAM (Security Accounts Manager)
database• Unix/Linux Files On Unix/Linux systems the password hashes are
stored in the /etc/shadow file
• Authentication Process • User enters password, Example: catdog • Hash is computed, Hash(catdog) = sMxYb7$og4uxH4oHXAVwf • The computed hash is compared to stored hash • Access granted or denied
Summary• Vulnerabilities are in ALL current popular
OS's– Hard to go beyond the “hype” to understand
how vulnerable you are given a certain OS– Try to discover for yourself how secure OS is
that you are using– Read bulletins, seek opinions of people you
trust and try to protect yourself– Buy add-on security products, disable OS
features, run with reduced privilege
References and Reading MaterialSecure Coding in Linux – Free Book
http://www.dwheeler.com/secure-programs/
Secure Coding Guidehttps://developer.apple.com/library/mac/
#documentation/security/Conceptual/SecureCodingGuide/Articles/TypesSecVuln.html
The End
Next Time: Specifics Windows vs. Linux, go over
Assignment