Practical Threat modelling

In Agile Projects

Chris Rutter

choss@outlook.com

Platform Security Engineer

Payments / Retail Banking / Government

https://www.linkedin.com/in/chris-rutter-1b74a8b0

Transformation Agile Project

  • New, shiny, market-driven functionality
  • Use Agile - Feedback from business each week
  • Hire DevOps engineers - All skills in team
  • Brand New Cloud IaaS / PaaS - Quick provision and scales up
  • Deliver MVPs and iterate - Quick Time to Market

Goal: Deliver an MVP in 12 weeks

Unique Security Challenge

Project Plan

Let's be Agile!

 

  • MVP Features defined
  • Create Feature-driven user stories
  • Estimate stories
  • Undocumented whiteboard designs
  • Work for 11 weeks
  • 1 week for security sign-off

Project Workflow

Week 10

Week 16

  • Security Design Review found high impact architectural issues
  • App Penetration Test found severe vulnerabilities
  • Secret management does not follow company standards
  • Review, fixes and verification are thrown over the wall and take weeks
  • Business Executive signs off on risk acceptance

Delivered 4 weeks late

Less Secure

Everyone hates/blames Security

Let's try that again

  • Threat modelling with developers at whiteboard stage
  • Identify risks and controls early
  • Design security into our architectures
  • Reduce sign-off time
  • Build trust between dev, ops and security
  • Educate developers & encourage to take security ownership

Threat Modelling as a collaborative exercise

Our Teams

DevSecOps Engineer / Security SME

  • Threat Models every sizeable design
  • Works with BAs to negotiate security user stories
  • Technical security knowledge resource
  • Faster change needs more of these!
  • Active feature Software developer
  • Part of every architectural design whiteboard
  • Point of contact for SME

Security SME

Devsecops / Security Champion

Personal Finance Insights App

Project Epic Backlog

Initial Internal Beta

Story Name Story Description Estimate
US-001 User can create account and log in with username and password 1 week
US-002 User can grant access to bank account using Open Banking / OIDC 2 weeks
US-003 User bank account information can be retrieved and stored 1 week
US-004 Mobile app can retrieve and display account information 1 week
US-005 Bank account transactions for last 3 months can be obtained async 1 week
US-006 Transactions can be viewed on mobile app 1 week
US-007 User can view total incomings and outgoings based on transaction type 1 week
US-008 Transactions can be categorised by purchase type 2 weeks
US-009 User can view total spending per purchase category for each month 1 week
total 11 weeks

Threat Model Triage

Sprint 0 - Project Epic Workshop

Story Name Story Description
US-001 User can create account and log in with username and password
US-002 User can grant access to bank account using Open Banking / OIDC
US-003 User bank account information can be retrieved and stored
US-004 Mobile app can retrieve and display account information

Triage continues for all new user stories

Sprint 1

Whiteboard Designs

  • Developers and SME whiteboard designs
US-001 User can create account and log in with username and password
  • Communcation Diagram
  • Sequence Diagram

Sprint 1

Threat Model

  • DevSecOps/SME document flows
  • Perform threat model with IT Security Function
  • STRIDE Analysis
  • Identify Vulnerabilties and controls
US-001 User can create account and log in with username and password

Sprint 1

Define Standards

  • IT Security confirm or define standards for controls
  • IT Security give initial indication of risk
  • Identify specific standards for controls
  • Early indication of highest security priorities
US-001 User can create account and log in with username and password

Sprint 1

Create Libraries and Implement Controls

  • DevSecOps engineer writes a small re-usable library to perform hashing complying with standards.  Implements in user story
  • Session storage on mobile app is reviewed with front-end developers so that keychain is used and session protected

All Controls are documented and verified instantly

Sprint 1

Create Security User Stories

Based on controls identified during threat modelling

Given: The authentication service requires a database user and credentials at runtime
Then: User permissions will be agreed and defined in code
And: Credentials will be generated and provided to app securely

Result

  • Security concerns are identified before code is written
  • Controls are pre-approved by IT Security
  • All reviews and controls are documented in parallel
  • Security is implemented with each user story (when possible)
  • Security-specific user stories are added to backlog immediately
  • IT Security gain valuable project knowledge each week
  • IT Security seen as experts rather than blockers

Huge reduction in unknown security work

Secure By Design

 

Questions?

Practical Micro Threat Modelling - DevSecOps Anniversary

By Chris Rutter

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Practical Micro Threat Modelling - DevSecOps Anniversary

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