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This presentation is part of one of talk, I gave in Microsoft .NET Bootcamp. The contents are slightly edited to share the information in public domain. In this presentation, I covered the significance and all related theory of Threat modeling and analysis.This presentation will be useful for software architects/Managers,developers and QAs. Do share your feedback in comments.
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Application Security-IIThreat Modeling and AnalysisLalit Kale
http://lalitkale.wordpress.com
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Overview
• Introduction• Why Threat Modeling?• Application Decomposition• Threat Mapping• Calculating Risks• Planning Threat Response & Risk Mitigations• Best Practices in Threat Modeling• Tools• Resources
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Introduction-Basic Terminology
• Asset: A resource of value, such as the data in a database or on the file system. A
system resource.
• Threat: A potential occurrence, malicious or otherwise, that might damage or
compromise your assets.
• Vulnerability: A weakness in some aspect or feature of a system that makes a
threat possible. Vulnerabilities might exist at the network, host, or application
levels.
• Attack (or exploit): An action taken by someone or something that harms an
asset. This could be someone following through on a threat or exploiting a
vulnerability.
• Countermeasure: A safeguard that addresses a threat and mitigates risk.
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What is Threat Modeling?
• A Strategic framework for planning application security aspect in system design phase
• Identify, understand, and mitigate threats most likely to affect the system
• Can be practiced for both new applications as well as on existing ones
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Why Threat Modeling?• Cannot build a secure system until you understand threats to
system
• Find security bugs early (and complex bugs)
• Address threats in logical order according to greatest risk
• Reduce overall risk by mitigating important threats
• How do you know when application is “secure enough”?
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Why Threat Modeling?
• Helps better understand your application
• Justification for security features and relation to identified threat
• Clearly documented assumptions and/or consequences
• Testers can specifically test against known threats
• Helps prevent duplication of security efforts
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Threat Modeling in Microsoft SDL
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Types of Threat Modeling• Attacker Centric
• Starts with an attack and evaluates the goals and how attackers might achieve them
• Software Centric• Starts from the design of system and attempts to step through a model
of system, looking for types of attacks against each element of the model
• Asset Centric• Involves starting from assets entrusted to a system, such as a collection
of sensitive personal information
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Threat Modeling Phases
Application Decomposition
Threat Mapping
Threat / Risk Rating
Threat Response & Mitigations
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Application Decomposition• Use modelling diagrams for a
visual representation of how the subsystems operate and work together
• The type of diagram is not important, but it should focus on data and how it flows through the system
• For instance, DFDs and Use Cases are useful
• But don’t go too deep - 2 or 3 levels is enough
Application Decomposition
Threat Mapping
Threat / Risk Ratin
g
Threat
Response & Mitigations
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Application Decomposition
1. Define scope
2. Create an architecture overview
3. Function
4. Logical architecture
5. Physical deployment
6. Technologies
7. Identify assets
8. Mark trust boundaries
9. Identify data flows, entry points, and assumptions
10. Make note of privileged code
Application Decomposition
Threat Mapping
Threat / Risk Ratin
g
Threat
Response & Mitigations
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Identifying Threats• Analyse each aspect of the architecture/design
• Ask questions with regards to attacker goals• Can the user’s identity be spoofed?• Can data be accessed without authorization?• Can the system be easily blocked?• …
• Compare application to common threats• Are Cross-Site Scripting (XSS) attacks relevant?• Is canonicalization an issue?• Can user sessions be hijacked?• …
• Use structured methods to identify threats
Application Decomposition
Threat Mapping
Threat / Risk Ratin
g
Threat
Response & Mitigations
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Identifying Threats• To identify threats or goals, ask the following questions:
• How can the adversary use or manipulate the asset to modify or control the system?
• Retrieve information within the system?• Manipulate information within the system?• Cause the system to fail or become unusable?• Gain additional rights?
• Can the adversary access the asset - • Without being audited?• And skip any access control checks?• And appear to be another user?
Application Decomposition
Threat Mapping
Threat / Risk Ratin
g
Threat
Response & Mitigations
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STRIDE Model• A common model for classifying attacker goals is the STRIDE model:
• Spoofing – Posing as another user, component, or external system that should be identified by the system
• Tampering – Unauthorized modification of data
• Repudiation – Denying performing an action without the system being able to prove otherwise
• Information Disclosure – Exposure of protected data to an unauthorized user
• Denial of Service – Disallowing valid users to access the system
• Elevation of Privileges – Gaining privileged access by a lower privileged user
Application Decomposition
Threat Mapping
Threat / Risk Ratin
g
Threat
Response & Mitigations
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Threat Tree• Method to explore valid attack paths
• Represents conditions needed to exploit the threat
• Determine all the combined vulnerabilities associated with a threat
• Focus on mitigating the vulnerabilities that form the “path of least resistance”
Application Decomposition
Threat Mapping
Threat / Risk Ratin
g
Threat
Response & Mitigations
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Documenting Threats• Each threat should be documented with
1. Title2. Target component3. Vulnerability Categorization(s) (e.g. STRIDE)4. Attack techniques (e.g. threat tree)5. Risk6. Mitigation
Application Decomposition
Threat Mapping
Threat / Risk Ratin
g
Threat
Response & Mitigations
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Calculating Risks: RPD Model• How do I measure risk?
• Use a structured methodology• Predefine general values to avoid confusion
• Record the calculated risk
• Simple formula:• Risk = Probability * Damage Potential• Define expected damage for each value• Divide scale in three bands: High, Medium, Low• Simple, yet lacking dimension • Not always easy to agree…
Application Decomposition
Threat Mapping
Threat / Risk Ratin
g
Threat
Response & Mitigations
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Calculating Risks: DREAD Model
• Another method for determining risk is DREAD model
• Damage potential – How great is the damage if the vulnerability is exploited?
• Reproducibility – How easy is it to reproduce the attack?
• Exploitability – How easy is it to launch an attack?
• Affected users – As a rough percentage, how many users are affected?
• Discoverability – How easy is it to find the vulnerability?
• Risk = Min(D, (D+R+E+A+D) / 5)
• Agree beforehand on values of each factor
Application Decomposition
Threat Mapping
Threat / Risk Ratin
g
Threat
Response & Mitigations
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Threat Resolution & Risk Mitigation
• Threats can be resolved by• Risk Acceptance - doing nothing• Risk Transference - pass risk to an externality• Risk Avoidance - removing the feature/component that causes the risk• Risk Mitigation - decrease the risk
• Mitigation strategies should be examined for each threat
• Mitigations should be chosen according to the appropriate technology
• Resolution should be decided according to risk level and cost of mitigations
Application Decomposition
Threat Mapping
Threat / Risk Ratin
g
Threat
Response & Mitigations
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Best Practices in Threat Modeling
• Use structured & consistent methodologies
• Predefine and agree on risk ratings that work for you
• Include all relevant shareholders in TM discussions:• Security• Architecture / Design• Coding
• Testing
• Don’t let TM discussions to degenerate to finding solutions before
the threats have been fully identified
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Best Practices in Threat Modeling• Don’t model too deep – don’t get carried away in the details
• Document TM results so they could be used later on for:• Next versions• Similar products / systems• Education
• Use common attack libraries / patterns for consistency and additional ideas e.g.
http://www.owasp.org/index.php/Category:Attack
• Always remember – its never too late for Threat Modeling!
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Threat Modeling Tools
• The Threat Analysis and Modeling Tool (TAM):
• is an asset-focused tool designed for LOB applications.
• It is used for applications for which business objectives,
deployment pattern, and data assets and access control are
clearly defined.
• The focus of the tool is to understand the business risk in the
application, help identify controls needed to manage that
risk, and protect the assets.
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Threat Modeling Tools
• The SDL Threat Modeling Tool:
• is a software-focused tool designed for rich client/server
application development (for example, Windows and SQL
Server, among others)
• The tool assumes the final deployment pattern of the product is
unknown (that is, if it will be used to manage business-critical
applications with customer credit cards or not), so the focus of
the tool is to ensure security of the software’s underlying code.
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Application Decomposition
• Define scope• Create an
architecture overview
• Function• Logical architecture• Physical deployment• Technologies• Identify assets • Mark trust
boundaries• Identify data flows,
entry points, and assumptions
• Make note of privileged code
Threat Mapping
• Identifying Threats• Use STRIDE Model• Creating Threat Tree• Documenting each
Threat
Calculate Risks
• Use Risk = Probability * Damage Potential
• Use Risk = Min(D, (D+R+E+A+D) / 5)
Threat Resolution and Risk Mitigation
• Risk Acceptance - doing nothing
• Risk Transference - pass risk to an externality
• Risk Avoidance - removing the feature/component that causes the risk
• Risk Mitigation - decrease the risk
• Mitigation strategies should be examined for each threat
• Mitigations should be chosen according to the appropriate technology
• Resolution should be decided according to risk level and cost of mitigations
Summary
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Resources• OWASP (Open Web Application Security Project):
https://www.owasp.org
• Microsoft Security:
http://www.microsoft.com/security
http://www.Microsoft.com/sdl
• Wikipedia:
http://en.wikipedia.org/wiki/Threat_model
.
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http://creativecommons.org/licenses/by-nc-sa/4.0/
All trademarks are the property of their respective owners. Lalit Kale makes no warranties, express, implied or statutory, as to the information in this presentation.
Lalit [email protected]
http://lalitkale.wordpress.com
