Uncovering Supply Chain Risks with Penetration Testing

When you build a modern web application, how much of the code did your team actually write? 50%? 20%? Less?

And no, I’m not talking about “vibe coding” or features built on pure intuition. I’m talking about the code you didn’t write at all.

Your application’s attack surface isn’t just the code you commit. It’s a complex network of open-source libraries, third-party APIs, SaaS integrations, and cloud infrastructure. This is your software supply chain, and it’s full of hidden risks.

Standard vulnerability scanning can find outdated libraries, but it often misses the real-world impact of a weak link. This is where penetration testing moves from a theoretical checklist to a practical risk-finding mission. A pentest doesn’t just ask “Is this library old?” It asks, “Can I leverage this third-party integration to compromise your data?”

Here’s how web app penetration testing and infrastructure penetration testing uncover these deep, interconnected risks.

1. Third-Party Dependencies: The Code You Trust Implicitly

Modern development is built on open-source packages and third-party scripts. Your package.json, requirements.txt, or pom.xml file is a direct map of external code running with the full trust of your application.

The most obvious risk here is a vulnerable component. A pentester won’t just report an old library version; they will actively try to exploit its known vulnerability or at least develop a good proof of concept that demonstrates what attackers could do, giving you a clear way to prioritize based on real-world risk.

This concept extends to the build process itself, where a pentester might attempt a dependency confusion attack, tricking your system into downloading a malicious package from a public repository, which can lead to a compromise of your build pipeline.

The risk also lives on the client side. A web app penetration testing engagement will scrutinize those third-party marketing, analytics, or support chat scripts. If one of them is compromised in a Magecart-style attack, they can capture user data and session cookies directly from your customers’ browsers.

2. Misconfigured Integrations: The “Trusted” Connections

Your application does not live in isolation. It talks to Stripe for payments, SendGrid for emails, and dozens of other microservices and APIs. Each of those connections can become an entry point.

These risks often start with leaked API keys and over-privileged tokens. Pentesters hunt for keys hard-coded in JavaScript, mobile apps, or code repositories. More importantly, they test the permissions of those keys. We might find that a key meant only for sending emails is also privileged to read all company emails, a massive data leak waiting to happen.

Another classic supply chain attack is Server-Side Request Forgery (SSRF). A pentester may find a feature, like a “check stock” or “generate PDF from URL” function, that forces your server to make a request to an arbitrary URL. This can be used to scan your internal network from the inside, query internal-only services, or extract sensitive metadata from your cloud provider.

This vulnerability also applies to incoming data. If your application accepts incoming webhooks from a third-party service, a pentester will test if they can spoof a “payment successful” or “user verified” message from that trusted partner, potentially bypassing business logic and security controls.

3. Infrastructure Dependencies: The Foundation You Build On

Your application also relies on the infrastructure supporting it. It runs on a complex stack of cloud services, containers, and orchestration tools. A single misconfiguration in this foundational layer can undermine your entire security posture.

This is where an infrastructure penetration testing engagement becomes critical, as the findings are often the most common and high-impact. This includes issues like public S3 buckets, exposed database snapshots, and overly permissive IAM (Identity and Access Management) roles.

An infrastructure pentest will test if an IAM role intended for one EC2 instance can be used to access data in a “secure” S3 bucket, demonstrating a critical failure in segmentation.

This scrutiny also applies to the CI/CD pipeline, your supply chain’s assembly line. Pentesters will probe it for vulnerabilities, such as a developer with read-only access being able to inject code into the main branch or a compromised build-server’s secrets being used to pivot into the production environment.

Finally, the test examines container insecurity. Your application code may be secure, but the test will analyze the base Docker image it’s built on for known vulnerabilities, hard-coded secrets, and misconfigurations that allow for container escape or privilege escalation.

From “Maybe” to “Demonstrable” Risk

A software supply chain is all about trust. You trust your open-source libraries, your SaaS providers, and your cloud platform. A penetration test is the process of verifying that trust.

It provides the concrete, demonstrable evidence you need to prioritize fixes. It changes the conversation from “We have 200 medium-risk vulnerable packages” to “We used this single outdated library to gain access to your production server.”

A comprehensive web app penetration testing engagement, supported by regular infrastructure penetration testing, is a critical part of a healthy program to manage these complex, interconnected risks. Whether you’re preparing for a SOC 2 audit or securing a new product, a practical test is the only way to see the full picture.

Our free guide, Audit-Proof Your Pentest, gives you 17 questions that reveal whether you’re working with a true security partner or just another checkbox provider.

Learn how to identify red flags in communication, spot outsourced testing behind polished project managers, and choose a penetration testing company that values collaboration, clarity, and direct access to the people doing the work.