Protecting Web services and Web
applications against security threats
OWASP
AppSec
Europe
May 2006
Rix Groenboom
Support Manager
Parasoft UK Ltd
[email protected]
Copyright © 2006 - The OWASP Foundation
Permission is granted to copy, distribute and/or modify this document
under the terms of the GNU Free Documentation License.
The OWASP Foundation
http://www.owasp.org/
What We Will Explore
What threats we see today
Practices for securing Web Services and SOA
Use of a Policy based Approach:
 “Inside Out & Outside In”
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Structure of this presentation
Problems, Threats, and Solutions
“Testing Security Into The Application”
A Four-Step Approach To Securing SOAP
Examples of Threats Prevented
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Problems: Size and Complexity
3 MLOC of SW
50 lines
= 25 cm
100
= 50 cm
200
=1m
1,000
=5m
10 kloc
= 50 m
100 kloc
= 500 m
1 Mloc
= 5 km
3 Mloc
= 15 km
8 Mloc
= MARATHON
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Problems: Examples
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Problems: Examples
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Problems: XML Bomb
bomb.xml
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Problems: XML Bomb
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE SOAP-ENV:Envelope [
<!ELEMENT SOAP-ENV:Envelope ANY>
<!ATTLIST SOAP-ENV:Envelope entityReference CDATA #IMPLIED>
<!ENTITY x0 "Bomb!">
<!ENTITY x1 "&x0;&x0;">
<!ENTITY x2 "&x1;&x1;">
...
<!ENTITY x20 "&x19;&x19;">
<!ENTITY x21 "&x20;&x20;">
…
<!ENTITY x99 "&x98;&x98;">
]>
299 = 633825300114114700748351602688
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What is wrong with this picture ?
 Enterprise network
protected by
firewall
 Application is the
only way in
 Must keep
application open for
business
 User (potential
hackers) must have
access to the
application
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Software as a Service: Security Challenges
Legacy
Application
Logic
Database
Server
Application
Server
Thin
Client
Web
Site
Presentation
Layer
Web
Services
= Serious Security risks
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Software as a Service: Security Challenges
 Web services vulnerabilities can be present in the:
 Operating system or the applications that ship with it
 Network
 Database
 Web server
 Application server
 XML parser or Web services implementation / stack
 Application code
 XML appliance
 And, yes, that post-it note with the password under your
drawer or keyboard…
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Software as a Service: Security Challenges
Problems with Web services and SOA
Cut through firewall
 SOAP messages often travel over HTTP port 80
Business processes on the web
 Expose internal APIs to anonymous users
New technology, new mistakes
 Once web apps are locked tighter, guess who’s next?
Implied assumptions, external dependence
 “I can’t see it, neither can a hacker”
 “We can trust that service to work properly”
 “The use of the service is constrained by the client
application”
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Software as a Service: Security Challenges
 The Year2000 problem revisited !
 Gary McGraw (at CMU/SEI meeting)
 Y2K problem:
 Applications never designed to work > 30,40 years
 Source code contains root cause of the problems
 One defect (bug) is enough to cause serious problems
 And now with security:
 Applications never designed to be connected to networks /
internet
 Source code contains root cause of the problems
 One vulnerability is enough to cause serious risk
 And worse, people hunt for them !
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Securing Web Services – Solutions So far
 General Practices
 Define acceptable protocols
 Shut down other services
 Lock down firewall (change port)
 Enforce security mechanisms




Authentication
Access Control
Auditing
… to Z
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Securing Web Services – Solutions So far
 SOA Security Mechanisms
 WS-Security





XML Encryption
XML Signature
X509
Username Tokens
SAML
 WS-Trust
 WS-SecureConversation
 WS-SecurityPolicy
 WS-Federation
 WS-Privacy
 WS-*
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General Web Services Threats
Common to all Web applications
SQL Injections
 Special characters in queries
Capture and Replay Attacks
 Man in the middle attacks
DoS (resulting from a large load)
 Blow up application from inside
Improper Error Handling
 Dump of stack trace etc
Broken Access Control
 Take over earlier sessions tokens etc
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General Web Services Threats
Specific to XML Web services
Large Payloads
 Send huge XML load, or generate huge responses
XPath Injections
 Query XML documents for certain nodes
External Entity Attacks
 Misuse pointed to XML data using URI
XML Bombs
 Recursive XML entity declaration
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General Web Services Threats
However, threats also come from within:
Since 1999, the percentage of companies reporting a
computer-security incident from inside is almost the
same as those reporting it from the outside
28.9% of of security incidents come from employees
Source:
The Wall Street Journal Online (Feb 13, 2006)
http://online.wsj.com/article/SB113926053552466409
.html
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Challenge - Properly Addressing Security
Testing security “into” the Web service
application:
 Common “end-of-cycle” security testing can detect some standard
application security vulnerabilities, however…
 Approaching security merely as a “bug finding” exercise is inefficient and
costly
 It is impossible to cover all possible execution paths with testing!
Architect
Assumptions
Develop
Test
Need to be
able to detect
GAP
vulnerabilities as early as
possible.
Monitor
Audits
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Why More Testing Does Not Help ?
String username = request.getParameter("USER");
String password = request.getParameter("PASSWORD");
String query = “SELECT user_id FROM Users WHERE username=‘” +
username + “’ AND password=‘” + password + “’”;
Statement.execute(query);
An attacker passes ' or 1=1 #
for usersname
SELECT user_id FROM Users
WHERE username='' or 1=1 #' AND password=‘foo’
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Securing Web Services
A different approach is needed
A preventive, policy-based approach rather than a
reactive one
Security, like quality, must be built into the application
and cannot be tested in
Application are large and complex
We propose a combined approach:
Outside In
Inside Out
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Securing Web Services: Step 1
Assessment: Impact & Risk
Analyze the business process
 Assets, users, entry points
 What needs to be protected? How?
 Outsource for expertise before implementation
Define security threats
 CIA: Confidentiality, Availability, Integrity
 Risk = Threat x Vulnerability x Expected Loss
– Threat = Motivated Attacker with Path to Valuable Asset
– Vulnerability = Weakness in system
– Expected Loss = Impact of threat realization
 Misusage, the general WS threats, etc.
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Securing Web Services: Step 1
Assessment: Penetration Testing
Find a few general vulnerabilities
Many penetration activities can be automated
 Generate injection attacks, XSS, scan for broken access
control, etc.
 Simulate large loads, generate big messages, etc.
Penetration testing is not exhaustive
But, a vulnerability you find
 Is like a real bug: if you see one, there are 1000 you do not
see !
 “where smoke is, is fire” & “tip of the iceberg”
 Helps you in Step 2
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Securing Web Services: Step 2
Develop a Security Policy:
A security policy is a set of guidelines that are an
overall strategy for application security
Secure implementation guidelines:
Use trusted libraries
Adhere to coding and XML standards
 Release IO resources in the code
 Turn off DTD support in XML parsers
 Constrain schema types
Review implementation for errors
Turn off features by default
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Securing Web Services: Step 2
 However, security policy also covers applications code
 Key areas that need are required:
 Access control and Authentication
 Denial of Service
 Command Injection
 Concurrency
 Cryptography
 Error Handling
 Input Validation
 Logging
 Malicious Code
 Memory and Session Management
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Securing Web Services: Step 2
 Securing input to the application:
 Identify all input routines (like getparameter)
 Implement validation functions
 Check that all security related inputs are done from a
wrapper environment
 Securing output of the application:
 Identify all the output routines (like DB access)
 Write logging routines
 Check that all output routines are followed by logging
routine
 Make sure application does not through exceptions
etc
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Securing Web Services: Step 2
 Security Example: SQL Injection
String s = "SELECT User_id, Username FROM USERS
WHERE Username = '" + sUsername + "' AND
Password = '" + sPassword + "'";
…
Statement queryStatement =
connection.createStatement();
queryStatement.executeQuery(s);
 Imagine:
sUsername = ‘ or 1=1 #
sPassword = (ANY)
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Securing Web Services: Step 2
 Security Example: SQL Injection
PreparedStatement queryStatement = null;
try {
queryStatement = connection.prepareStatement(
"SELECT User_id FROM USERS WHERE
Username = ? AND Password = ?");
queryStatement.setString (1, user);
queryStatement.setString (2, password);
…
} catch { …
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Securing Web Services: Step 2
“Avoid Public
Data members”
class A {
public:
int a;
};
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Securing Web Services: Step 3
 Enforce Security Policy Throughout SDLC
 A policy without an automated enforcement mechanisms is
like law without police
 Available techniques:
 Static / Dynamic Code analysis
 Map policies to executable rules
 Configure the rules based on the policies and projects at hand
 Compliance SOA Development Governance in SDLC
 Like: SOAP, WSDL, Schema, XML Metadata.
 Runtime SOA Governance
 Management, Registry, Orchestration
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Securing Web Services: Step 4
Regression Testing
Software development is an iterative process
An iterative development process fails without
regression testing. The same applies to security
Fixing a security vulnerability should be coupled with a
policy and an enforcement mechanism to prevent it
from reoccurring again
Regression testing practices results in a visible quality
process that reinforces trust
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General Web Services Threats Prevented
SQL Injections
Policy: Validate user input; strip potentially malicious
characters like ‘ and “ as soon as you get them
Test: Penetrate, regression test
Capture and Replay Attacks
Policy: Use signed random nonce values and
Timestamps
Test: Penetrate, regression test
DoS (resulting from a large load)
Policy: Secure coding standards
Test: Simulate attacks, regression test
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General Web Services Threats Prevented
Improper Error Handling
Policy: Catch/handle all exceptions
Test: Penetrate, regression test
Broken Access Control
Policy: Baseline/extended security policies
Test: Positive & negative conditions, regression test
 Large Payloads
Policy: Constrain schema types
Test: Simulate attacks, regression test
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General Web Services Threats Prevented
XPath Injections
Policy: Validate user input at the entry point
Test: Simulate attacks, regression test
 External Entity Attacks
Policy: Disable DTD processing in XML parser
Test: Simulate attacks, regression test
 XML Bombs
Policy: Disable DTD processing in XML parser
Test: Simulate attacks, regression test
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Securing Web Services
 Old tricks for new dogs…
 Start from the beginning
 Assume the worst
 Use standards rather than “build your own”
 Be proactively consistent
 Consider external and internal threats
 Develop and enforce a security policy
 Compliance vs. Audit
 “Build it in”, not “test it in”
 Security is not a bug finding exercise (one is enough)
 Remember: Security is Y2K revisited
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Conclusion
Thank you
Resources
http://www.cgisecurity.com/ws/
http://www.oasisopen.org/committees/tc_cat.php?cat=ws
http://www.soaleaders.org/
Commercial
http://www.parasoft.com/
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