Threat modelling 101

Using abstractions to think about risks is a useful technique to identify the ways an attacker could compromise a system.

There are various approaches to perform threat modelling but at the core, it’s about understanding what we are building, what can go wrong with it and what we should do about it.

Here is a good video by SAFECode introducing the concept:

Software and Security Engineering


The Software and Security Engineering course taught at the University of Cambridge is available for free online. It includes video lectures, slide decks, reading materials and more.

Whether you are new to information security or a seasoned professional, this course will help you build solid foundations.

Lecture 9 covering critical systems is my favourite. It bring together previous discussions on psychology, usability and software engineering in the context of safety. It adds to the array of the case studies from Lecture 6, focusing on software failures and what we can learn from them. It also offers a fascinating analysis of the Therac-25 accidents and Boeing 737 Max crashes.

AWS Security Hub: all your security alerts in one place

Security Hub

If you are following my blog, you’ve probably noticed that I’ve been focusing on security-specific AWS services in my previous several posts. It’s time to bring them all together into one consolidated view. I’m talking, of course, about the AWS Security Hub.

Security Hub allows you to aggregate and centrally analyse security alerts and findings from Config, GuardDuty, IAM, Inspector, Firewall Manager and more.

Security Hub findings

You can group, filter and prioritise findings from these services in many different ways. And, of course, you can visualise and make dashboards out of them.

CIS exampleApart from consolidating findings from other services, it also assesses your overall AWS configuration against PCI DSS and/or the CIS Amazon Web Services Foundations Benchmark, which covers identity and access management, logging, monitoring and networking, giving you the overall score (example below) and actionable steps to improve your security posture.

CIS score

Similar to the many other AWS services, Security Hub is regional, so it will need to be configured in every active region your organisation operates. I also recommend setting up your security operations account as a Security Hub master account and then inviting all other accounts in your organisation as members for centralised management (as described in this guidance or using a script).

If you are not a big fan of the Security Hub’s interface or don’t want to constantly switch between regions, the service sends all findings to CloudWatch Events by default, so you  can forward them on to other AWS resources or external systems (e.g. chat or ticketing systems) for further analysis and remediation. Better still, you can configure automated response using Lambda, similar to what we did with Inspector findings discussed previously.

Setting up a Web Application Firewall in AWS


I wrote about automating application security testing in my previous blog. If you host your application or API on AWS and would like an additional layer of protection agains web attacks, you should consider using AWS Web Application Firewall (WAF).

It is relatively easy to set up and Amazon kindly provide some preconfigured rules and tutorials. AWS WAF is deployed in front of CloudFront (your CDN) and/or Application Load Balancer and inspects traffic before it reaches your assets. You can create multiple conditions and rules to watch for.

WAF conditions

If you’ve been configuring firewalls in datacentres before the cloud services became ubiquitous, you will feel at home setting up IP match conditions to blacklist or whitelist IP addresses. However, AWS WAF also provides more sophisticated rules for detecting and blocking known bad IP addresses, SQL Injections and Cross Site Scripting (XSS) attacks.

Additionally, you can chose to test your rules first, counting the times it gets triggered rather than setting it to block requests straight away. AWS also throw in a standard level of DDoS protection (AWS Shield) with WAF at no extra cost, so there is really no excuse not to use it.

Automating the detection and remediation of security vulnerabilities in AWS

Inspector dashboard

If you rely on EC2 instances in at least some parts of your cloud infrastructure, it is important to reduce the attack surface by hardening them. You might want to check out my previous blogs on GuardDuty, Config, IAM and CloudTrail for other tips on securing your AWS infrastructure. But today we are going to be focusing on yet another Amazon service – Inspector.

To start with, we need to make sure the Inspector Agent is installed on our EC2 instances. There are a couple of ways of doing this and I suggest simply using the Inspector service Advance Setup option. In addition, you can specify the instances you want to include in your scan as well as its duration and frequency. You can also select the rules packages to scan against.

Inspector setup

After the agent is installed, the scan will commence in line with the configuration you specified in the previous step. You will then be able to download the report detailing the findings.

Inspector findings

The above setup gives you everything you need to get started but there is certainly room for improvement.

It is not always convenient to go to the Inspector dashboard itself to check for discovered vulnerabilities. Instead, I recommend creating an SNS Topic which will be notified if Inspector finds new weaknesses. You can go a step further and, in the true DevSecOps way, set up a Lambda function that will automatically remediate Inspector findings on your behalf and subscribe it to this topic. AWS kindly open sourced a Lambda job (Python script) that automatically patches EC2 instances when an Inspector assessment generates a CVE finding.

You can see how Lambda is doing its magic installing updates in the CloudWatch Logs:

Commadn line update

Or you can connect to your EC2 instance directly and check yum logs:

yum update

You will see a number of packages updated automatically when the Lambda function is triggered based on the Inspector CVE findings. The actual list will of course depend on how many updates you are missing and will correspond to the CloudWatch logs.

You can run scans periodically and still choose to receive the notifications but the fact that security vulnerabilities are being discovered and remediated automatically, even as you sleep, should give you at least some peace of mind.

How to prevent committing secrets in code


Committing passwords, SSH keys and API keys to your code repositories is quite common. This doesn’t make it less dangerous. Yes, if you are ‘moving fast and breaking things’, it is sometimes easier to take shortcuts to simplify development and testing. But these broken things will eventually have to be fixed, as security of your product and perhaps even company, is at risk. Fixing things later in the development cycle is likely be more complicated and costly.

I’m not trying to scaremonger, there are already plenty of news articles about data breaches wiping out value for companies. My point is merely about the fact that it is much easier to address things early in the development, rather than waiting for a pentest or, worse still, a malicious attacker to discover these vulnerabilities.

Disciplined engineering and teaching your staff secure software development are certainly great ways to tackle this. There has to, however, be a fallback mechanism to detect (and prevent) mistakes. Thankfully, there are a number of open-source tools that can help you with that:

You will have to assess your own environment to pick the right tool that suits your organisation best.

If you read my previous blogs on integrating application testing and detecting vulnerable dependencies, you know I’m a big fan of embedding such tests in your Continuous Integration and Continuous Deployment (CI/CD) pipeline. This provides instant feedback to your development team and minimises the window between discovering and fixing a vulnerability. If done right, the weakness (a secret in the code repository in this case) will not even reach the production environment, as it will be caught before the code is committed. An example is on the screenshot at the top of the page.

For this reason (and a few others), the tool that I particularly like is detect-secrets, developed in Python and kindly open-sourced by Yelp. They describe the reasons for building it and explain the architecture in their blog. It’s lightweight, language agnostic and integrates well in the development workflow. It relies on pre-commit hooks and will not scan the whole repository – only the chunk of code you are committing.

Yelp’s detect-secrets, however, has its limitations. It needs to be installed locally by engineers which might be tricky with different operating systems. If you do want to use it but don’t want to be restricted by local installation, it can also run out of a container, which can be quite handy.

How to integrate application security testing in the CI/CD pipeline


In this blog I’m going to build on my previous posts on agile security, DevSecOps culture and managing vulnerabilities in open source libraries to talk about automating application security testing.

Read the rest of this entry »

Agile security. Part 2: User stories


In the previous blog, I wrote about how you as a security specialist can succeed in the world of agile development, where the requirements are less clear, environment more fluid and change is celebrated not resisted.

Adjusting your mindset and embracing the fact that there will be plenty of unknowns is the first step in adopting agile security practices. You can still influence the direction of the product development to make it more resilient, safe and secure by working with the Product Owner and contributing your requirements to the product backlog.

Simply put, product backlog is a list of desired functionality, bug fixes and other requirements needed to deliver a viable product. There are plethora of tools out there to help manage dependencies and prioritisation to make the product owner’s job easier. The image at the top of this post is an example of one of such tools and you can see some example requirements there.

As a security specialist, you can communicate your needs in a form of user stories or help contribute to existing ones, detailing security considerations. For example, ”Customer personal data should be stored securely” or “Secure communication channels should be used when transmitting sensitive information”. Below are a couple more examples from different categories.

Ticket 2Ticket 1

When writing security user stories, you should try and elaborate as much as possible on the problem you are trying to solve, what value it will provide if solved and the acceptance criteria. Each story will then have points assigned which signifies how much effort a particular functionality will require. The process of arriving to the final number is quite democratic and usually involves playing planning (sometimes also called Scrum) poker in which every developer will estimate how long each story is going to take with some discussion and eventual consensus. You can do it with an app as on the image below, or the old school way with a deck of cards. 

Scrum poker

You don’t have to use the above number pattern, and opt-in instead for the Fibonacci sequence or T-shirt sizes.

It’s important that the security team is involved in sprint planning to contribute to the estimates and help the product owner with prioritisation. Other Scrum meetings, like backlog refinement and daily stand-ups are also worthwhile to attend to be able clarify your requirements (including value, risk, due dates and dependencies) and help remove security related impediments.

A culture of collaboration between teams is essential for the DevSecOps approach to be effective. Treating security as not something to workaround but as a value adding product feature is the mindset product and engineering teams should adopt. However, it’s up to security specialists to recognise the wider context in which they operate and accept the fact that security is just one of the requirements the team needs to consider. If the business can’t generate revenue because crucial features that customers demand are missing, it’s little consolation that security vulnerabilities have been addressed. After all, it’s great to have a secure product, but less so when nobody uses it.

How to manage vulnerabilities in your open source packages. Part 2: Integrating Snyk in your CI/CD pipeline

We learnt how to detect vulnerable packages in your projects using Snyk in the previous blog. Here, in the true DevSecOps fashion, I would like outline how to integrate this tool in your CI/CD pipeline.

Although the approach described in the previous blog has its merits, it lacks proactivity, which means you might end up introducing outdated packages in your codebase. To address this limitation, I’m going to describe how to make Snyk checks part of your deployment workflow. I’ll be using CircleCI here as an example, but the principles can be applied using any CI tool.

A step-by-step guidance on configuring the integration is available on both the Snyk and CircleCI websites. In the nutshell, it’s just about adding the Snyk Orb and API to CircleCI.

After the initial set-up, an additional test will be added to your CircleCI workflow.


If vulnerabilities are identified, you can set CircleCI to either fail the build to prevent outdated libraries to be introduced or let the build complete and flag.


Both methods have their pros and cons and will depend on the nature of your environment and risk appetite. It’s tempting to force the build fail to prevent more vulnerable dependencies being introduced but I suggest doing so only after checking with your developers and remediating existing issues in your repositories using the method described in the previous blog.


Snyk’s free version allows you only a limited number of scans per month, so you need to also weigh costs agains benefits when deploying this tool in your development, staging and production environments.

This approach will allow you to automate security tests in a developer-friendly fashion and hopefully bring development and security teams closer together, so the DevSecOps can be practiced.

How to manage vulnerabilities in your open source packages. Part 1: Using Snyk

We rely on open source libraries when we write code because it saves a lot of time (modern applications rely on hundreds of them), but these dependencies can also introduce vulnerabilities that are tricky to manage and easy to exploit by attackers.

One way of addressing this challenge is to check the open source packages you use for known vulnerabilities.

In this blog I would like to discuss how to do this using an open source tool called Snyk


The first thing you want to do after creating an account is to integrate Snyk with your development environment. It supports a fair amount of systems, but here I would like to talk about GitHub as an example. The process of getting the rest of the integrations are pretty similar.

Snyk’s browser version has an intuitive interface and all you need to do is go to the Integrations tab, select GitHub and follow the instructions.

After granting the necessary permissions and selecting the code repositories you want tested (don’t forget the private ones too), they will be immediately scanned.

You will be able to see the results in the Projects tab with issues conveniently ordered by severity so you can easily prioritise what to tackle first. You can also see the dependency tree there which can be quite handy.


A detailed description of the vulnerability and some recommendations on how to remediate it are also provided.

Most vulnerabilities can be fixed through either an upgrade or a patch and that’s what you should really do, or ask someone (perhaps by creating a ticket) if you don’t own the codebase. Make sure you test it first though as you don’t want the update to break your application.

Some fancy reporting (and checking license compliance) is only available in the paid plan but the basic version does a decent job too.

You can set up periodic tests with desired frequency (daily or weekly) which technically counts as continuous monitoring but it’s only the second best option compared to performing tests in your deployment pipeline. Integrating Snyk in your CI/CD workflow allows to prevent issues in your code before it even gets deployed. This is especially useful in organisations where code gets deployed multiple times a day with new (potentially vulnerable) libraries being introduced. And that’s something we are going to discuss in my next blog.