Today, application security must be built in from the outset and reinforced continually throughout the software lifecycle. Even organizations with mature development practices need automated tools to successfully secure their software in complex, fast-changing environments. This post compares three widely used categories of AppSec tools: static application security testing (SAST), dynamic application security testing (DAST), and interactive application security testing (IAST). We explain how these tools work, explore the strengths and tradeoffs, and help you select tools that work for your unique organization.
Why you need AppSec tools
Multiple converging trends are making software harder to secure – and increasing the risks for users. Code bases keep growing larger and more complex, with more internal and external interactions than ever. Cloud-native and microservice-based development approaches present new challenges. Software draws on components from more sources, in multiple languages, with varying provenances.
All this adds up to security complexity that’s beyond the abilities of any dev team to manage manually. Teams need automation and smarter tools to help identify and understand problems earlier and fix them faster.
Attackers know how vulnerable you are, which is why they’re especially focused on web application software. In Verizon’s 2022 Data Breach Investigations Report, roughly 45% of attacks and 70% of incidents were associated with web application hacking. With that ominous statistic in mind, let’s turn to your options for tools that promise to help you avoid becoming the next data breach headline.
Different types of web security tools
No single category of tool can cover every aspect of web application security, so organizations typically combine multiple AppSec tools to protect applications throughout their lifecycle. Security testing is the crucial foundation of application security, allowing you to find and remediate issues all across the development and operations pipeline. We’ll consider the major categories of application security testing tools in turn.
Static application security testing (SAST)
SAST tools automatically review source code, bytecode, or binaries before the application is deployed to identify vulnerabilities so they can be fixed long before they cause damage. SAST tools may also be used to help software teams make sure all code conforms to their own internal coding standards and guidelines. SAST is also sometimes called white box testing or inside-out testing – referring to the fact that it is looking inside the code to pinpoint the exact location of vulnerabilities. By automating code security reviews, SAST tools make it practical to check both complete code bases and individual parts of an application. Developers can see the exact location of each potential issue and get feedback even if the code in question isn’t yet part of a live, running system. This facilitates more rapid fixes and can help prevent developer mistakes in the future.
Being tied to source code also imposes some limitations on SAST tools. For one thing, they require access to the code, and sometimes that can’t be provided, especially for third-party modules or products. They also have little visibility into the context where software operates and have developed a reputation for generating false positives. They are tied to specific languages, which can present problems when software combines code in multiple languages. And finally, SAST cannot find issues that only appear at runtime, such as misconfigurations, business logic vulnerabilities, or vulnerabilities introduced by dynamic dependencies.
Dynamic application security testing (DAST)
DAST tools check the security of running applications in real-world environments, probing them from the outside in by safely mimicking attacker behaviors. Since DAST works from the outside with no visibility into source code, it’s sometimes called black box testing.
Because DAST doesn’t require access to source code, it can be used with applications written in virtually any language or combination of languages. In web applications, DAST tools can uncover misconfigurations, encryption or authentication problems, and exploitable vulnerabilities to attacks such as server-side request forgeries and SQL injection. Since DAST requires a running application, it’s typically used during the later stages of software development.
Running DAST as early as possible in the pipeline, for instance on build candidates, helps with catching issues before they become harder to fix, but not all tools support that kind of process. Because they don’t have source code access, most DAST tools will also struggle to pin down the exact location and cause of a vulnerability. While DAST is far easier to set up compared to SAST and can theoretically run on any environment, running tests in production requires careful tuning to avoid performance problems, especially with less advanced tools. The best practice is thus to test a clone of the production environment.
Interactive application security testing (IAST)
IAST tools or gray box testing systems draw on elements of both SAST (white box) and DAST (black box) approaches, aiming to combine their respective strengths. IAST typically links to a running app and provides insight into its internal workings via a separate set of test results. IAST might be triggered by a test suite during the build process or by a DAST scanner.
When analyzing a running app, IAST can potentially draw on runtime information such as configurations, calls, HTTP traffic, data and control flow, infrastructure data, and the behavior of middleware services. It simultaneously analyzes the app’s source code, attempting to connect these external and internal views to identify additional vulnerabilities and where they occur in the code. Some IAST tools can also perform software composition analysis (SCA) to identify open-source code components within the application, highlight known vulnerabilities, and ensure license compliance.
To be fully interactive, an IAST tool should actively provide and respond to information throughout the entire testing process. For example, Invicti’s Shark IAST module attaches to the application runtime and as the DAST scan engine detects vulnerabilities, the IAST sensor fills out the details – from line numbers to injected payloads, exploit results to stack traces. This is crucial additional information that developers can act on immediately.
How to choose the right tools for your team
As you plan investments in AppSec tooling, there are many factors to consider. Here are just a few of them, with examples for various types of tools:
- Effectiveness. How do the tools you’re considering stack up on authoritative industry measurements? Taking DAST as an example, how did the tool perform in tests such as Shay Chen’s web vulnerability scanner benchmark? Can the tool find everything you need to see, including unlinked and hidden files that some scanners miss?
- False positives. If your security engineers or developers can’t trust a tool’s alerts, they must manually validate everything it tells them. That’s expensive and fundamentally incompatible with rapid development. How can you prevent this for a tool like DAST? How well does it succeed? For example, with Invicti’s Proof-Based Scanning, vulnerabilities are examined by safely executing finely-tuned test attacks: 94% of direct-impact vulnerabilities are confirmed automatically, and fewer than 0.02% of vulnerabilities confirmed turn out to be false positives.
- Ease of deployment, use, and management. Some early IAST tools required complex integration and generated sizable performance impacts. What will it take to get started and then go live with the tool? Is it easy to integrate with your issue tracking system? Does it balance usability with capabilities?
- Compatibility. As mentioned earlier, SAST tools are necessarily language-specific and might not cover all the technologies, libraries, or frameworks in your environments. Will the tool work for you out of the box, or at least with easily available add-ons? Or will you need to purchase, set up, and manage multiple tools?
- Team empowerment. Will the tool help you move towards DevSecOps or other modern methodologies? Will it help you embed AppSec earlier (“shift left”) and throughout your SDLC? Will it help improve collaboration and eliminate silos? Will it make developers more productive and effective? When you’re using a DAST scanner with no access to the source code, is it going to deliver vague information that triggers finger-pointing, or will you get detailed bug reports accompanied by proof?
The importance of choosing the right AppSec tools
All AppSec tools are not equal. The wrong AppSec tools can add complexity and frustration to an already challenging development environment. But the right tools can give you confidence that your software is as attack-resistant as possible, as early as possible – and that your teams are continually learning, improving, and collaborating.