CSCD 303Essential Computer SecuritySpring 2013

Lecture 8 - Desktop Security

OS Security ComparedReading: See References

Overview

• Briefly, Overview of Linux Security • OS Vulnerabilities

• Linux• Windows• Max OS X

Linux Security Model

• Linux’s traditional security model is– People or processes with “root”

privileges can do anything– Other accounts can do much less

• Hence attacker’s goal– Get root privileges !!!!

File System Security

• In Linux everything is a file• I/O to devices is via a special file

– Example: /dev/cdrom allows access to the cdrom drive which is a special file

• Have other special files like named pipes– A conduit between processes / programs

• Since almost everything is a file – security very important

Users and Groups

• Users and Groups are not files• Users

– Someone or something capable of using files– Can be human or process– e.g. lpd (Linux Printer Daemon) runs as user lp

• Groups– List of user accounts– User’s main group membership specified in

/etc/passwd– User can be added to additional group by editing

/etc/group– Command line -> useradd, usermod, and userdel

• User's details are kept in /etc/password maestro:x:200:100:Maestro Edward Hizzersands:/home/maestro:/bin/bash

x in password file means password is stored in the shadow file

Entry in /etc/shadow password file maestro:$1$fnfffc$pGteyHdicpGOfffXX4ow#5:13064:0:99999:7:::

• Additional group details in /etc/groupconductors:x:100:

pianists:x:102:maestro,volodya

Users and Groups

File Permissions

• Files have two owners: a user & a group– Each with its own set of permissions– With a third set of permissions for other

• Permissions are to read/write/execute in order user/group/other

rw-rw -r-- 1 maestro user 35414 Mar 25 01:38 baton.txt

• Permission can be changed using chmod command

88

ACL:Default Permission and Abbreviation

Example: UNIX

Three classes of users: owner, group, all others

Directory Permissions

• Permissions on folder slightly works different– read = list contents– write = create or delete files in directory– execute = use anything in or change working

directory to this directory

drwxr-x--- 8 biff drummers 288 Mar 25 01:38 extreme_casseroles

Comparing Operating Systems

• Researchers have spent a lot of time studying vulnerabilities in operating systems• Which is better? Linux vs. Windows vs. Mac? Who has the fewest serious vulnerabilities?

• Other metric used -- how many successful attacks on a particular OS

Windows Design Flaws/Poor Design Decisions

• Windows has evolved from a single-user design to a multi-user model few years back

• Windows is monolithic, not modular, by design

• Windows depends too heavily on an RPC model

• Windows focuses on its familiar graphical desktop interface

Windows Evolved from Single-User Design to multi-user model

• Windows has long been hampered by its origin as Single-user system

– Windows originally designed to allow both users and applications free access to entire system, which means anyone could tamper with a critical system program or file

• Windows XP was the first version of Windows to reflect a serious effort to isolate users from the system,

• Users each have their own private files and limited system privileges– This caused many legacy Windows applications to fail– Solution: Windows XP includes a compatibility mode - a

mode that allows programs to operate as if they were running in the original insecure single-user design

Linux Based on Multi-User Design• Linux does not have a history of being a

single-user system– Has been designed from ground-up to isolate

users from applications, files and directories that affect entire operating system

• Each user is given a user directory• All of user’s data files and configuration

files are stored– When a user runs an application, such as a

word processor, that word processor runs with restricted privileges of the user

National Vulnerability Database

National Vulnerability Database Classifies and organizes reported vulnerabilities

for various software programs and systems Mitre has the contract to maintain this

database

http://web.nvd.nist.gov/view/vuln/search?execution=e2s1

You can search this database for all the vulnerabilities associated with a system

Evaluation: Windows Vs. LinuxVulnerabilities• The United States Computer Emergency Readiness Team

(CERT) uses its own set of metrics to evaluate severity of any given security flaw

• Query CERT vulnerabilities notes database for “Windows” and “Linux” keywords to examine metrics for 40 most recent reported vulnerabilities

• A number between 0 and 180 expresses final metric, where number 180 represents the most serious vulnerability

• The ranking is not linear– In other words, a vulnerability ranked 100 is not

twice as serious as a vulnerability ranked at 50• CERT considers any vulnerability with a score of 40 or

higher to be serious enough to be a candidate for a special CERT Advisory and US-CERT technical alert

National Vulnerability Database

National Vulnerability Database Classifies and organizes reported

vulnerabilities for various software programs and systems

Mitre has the contract to maintain this database

http://web.nvd.nist.gov/view/vuln/search?execution=e2s1

CERT: Query Result for Keyword “Microsoft”

CERT: Query Result for Keyword “Microsoft” (continued)

CERT: Query Result for Keyword “Linux”

CERT: Query Result for Keyword “Linux” (continued)

CERT: Evaluation of Query Results for Microsoft and Linux• CERT web search capabilities do not produce

perfectly desirable results in terms of granularity or longevity

– Especially True for Linux• The “Linux” search results include a number of

Oracle security vulnerabilities that are common to Linux, UNIX, and Windows

– In Top 40 CERT results for “Microsoft”, • Top entry containing the severity metric of 78• 5 entries have a severity rating of 40 or greater

– In Top 40 CERT results for Linux• Top entry containing the severity metric of 26.52• None other entry have a severity rating 27 or greater

Vulnerabilities

http://blogs.zdnet.com/security/?p=758

• Recent years, lots of comparisons – 2007 brought improved security with

Windows Vista and Mac OS X Leopard – Compiled security flaws in Mac OS X and

Windows XP and Vista and placed them side by side– Vulnerability statistics from third party

vendor Secunia and broke them down by Windows XP flaws, Vista flaws, and Mac OS X flaws

Table of Flaws Windows vs. Mac

Windows XP, Vista, and Mac OS X vulnerability stats for 2007

XP Vista XP + Vista Mac OS X

Total extremely critical 3 1 4 0

Total highly critical 19 12 23 234

Total moderately critical 2 1 3 2

Total less critical 3 1 4 7

Total flaws 34 20 44 243

Average flaws/month 2.8 1.7 3.7 20.3

Analysis of Data

• Apple had more than 5 times number of flaws per month than Windows XP and Vista in 2007–Most of these flaws were serious– This seems to go against conventional

wisdom

• Noteworthy ... –Windows Vista showed fewer flaws than

Windows XP, Windows Defender and Sidebar added 4 highly critical flaws to Vista that weren’t present in Windows XP

Update - Pwn2Own 2009• Want to guess the results of 2009?– Charlie Miller has done it again– 2nd consecutive year, security researcher hacked

into a fully patched MacBook computer by exploiting a security vulnerability in Apple’s Safari browser

– Miller launched his drive-by attack and claimed the $10,000 top prize. He also got to keep the MacBook machine

– Miller said he came to the CanSecWest security conference with a plan to hack into Safari and had tested the exploit carefully to ensure “it worked the first time.”

http://www.zdnet.com/blog/security/pwn2own-2009-safarimacbook-falls-in-seconds/2917

Current results https://en.wikipedia.org/wiki/Pwn2Own

Microsoft Vulnerabilities

http://www.sans.org/top-cyber-security-risks/#trends

• September 2009• For past six months, over 90% of the attacks

recorded for Microsoft targeted the buffer overflow vulnerability described in the Microsoft Security Bulletin MS08-067

References

The Register Security Report: Linux vs. Windows

http://www.theregister.co.uk/2004/10/22/security_report_windows_vs_linux/#execsummary

http://blog.loaz.com/timwang/index.php/2008/03/30/security_vulnerability_showdown_mac_os_v

Security vulnerability showdown, Mac vs. Linux vs. Ubuntu

http://blog.loaz.com/timwang/index.php/2008/03/30/security_vulnerability_showdown_mac_os_v

IBM report: Vulnerabilities still going unpatched

http://news.cnet.com/8301-1009_3-10154662-83.html

Mac versus Windows vulnerability stats for 2007

http://blogs.zdnet.com/security/?p=758

The End