What Is Static Application Security Testing (SAST)?
Static Application Security Testing (SAST) is a code testing tool that analyzes application source code to identify security vulnerabilities. SAST has been a popular tool among developers for at least a decade. It helps discover vulnerabilities so developers can fix the source code before releasing the application.
SAST is a type of white box testing, analyzing applications from the inside—the testers know how the code works. Teams use SAST tools early in the software development lifecycle (SDLC) to source code, byte code, and binaries for design and coding flaws, as part of a DevSecOps work method.
While SAST is useful, it is not well suited to modern cloud-native applications. We’ll describe the benefits of SAST, explain its pros and cons in today’s IT environment, and show the difference between SAST and competing security technologies.
In this article:
What Security Problems Does SAST Solve?
SAST operates early in the software development lifecycle (SDLC)—it doesn’t need a working application and can work without running any code. This approach allows developers to identify vulnerabilities early in the SDLC and quickly fix them before introducing breaking changes or security vulnerabilities to production.
A SAST solution gives developers real-time feedback while coding and helps address issues before the code progresses to the next stage in the SDLC. It prevents teams from treating security issues as an afterthought. The SAST tool provides detailed information about security issues, helping developers and security teams navigate the code to easily discover and fix the issue.
Some SAST tools pinpoint vulnerabilities and identify insecure code. They can also give detailed instructions on what part of the code needs fixing and how to fix it. They do not require deep security expertise.
Developers can use a SAST tool to create the custom reports they need. They can export these reports offline and track them via a dashboard. By systematically tracking all security issues reported by the SAST solution, developers can quickly fix and bring applications to market with minimal issues. This process helps ensure a secure SDLC.
Continuous security requires regularly running SAST solutions on applications—for example, on a daily or monthly basis, during routine builds, whenever a developer checks in code, and before code releases.
Related content: Read our guide to DevSecOps tools
SAST Testing Pros and Cons
SAST tools are useful for detecting common vulnerabilities, offering important benefits such as:
- Early security testing—SAST can work without executable code, making it suitable for the early stages of the SDLC. Testing applications from the initial coding phase helps reduce the time and cost required to fix the identified vulnerabilities.
- Common vulnerability detection—SAST helps identify code patterns that may indicate a common vulnerability listed in the Common Vulnerabilities Enumeration (CVE) and OWASP Top 10 lists.
However, SAST solutions have the following limitations:
- Language-specific—SAST solutions read and analyze the application source code, so they must support its programming language. Finding a SAST tool that can read all the necessary languages is often a problem for organizations that use multiple or less popular languages.
- Limited detection capabilities—not all vulnerabilities are detectible using SAST. These tools only analyze source code, not running applications, making them blind to non-code vulnerabilities at runtime and configuration errors.
- False positives—SAST tools don’t analyze application performance at runtime, so there is no way to determine if a potential vulnerability is a false positive or a real threat. SAST results require further analysis to distinguish the real risks.
- Time-consuming—SAST testing often takes time and requires frequent scans. Each SAST report analyzes a code snapshot, so it can quickly become outdated.
Is SAST Suitable for Cloud Native Applications?
While SAST is a powerful tool for legacy applications, its characteristics make it a poor choice for cloud native applications, such as those based on container or serverless technology. Here are some of the drawbacks of SAST in cloud apps.
Lack of Context
Cloud applications typically comprise many components, with different teams handling each. The components can only communicate during runtime. Static testing doesn’t involve running the code, so the SAST tool cannot see how it behaves at runtime. Each component scan is independent, overlooking vulnerabilities that affect inter-component communication.
Scanning code before running the application in the cloud can lead to many false positives and overlooked vulnerabilities.
While SAST solutions scan lists of known vulnerabilities to determine if they are present in the code, they can’t tell which code the app uses. False positives often result from non-exploitable vulnerabilities, adding to the developers’ workload.
On the other hand, SAST tools cannot detect cloud-specific vulnerabilities. They don’t identify cloud configuration issues and often miss services and APIs interacting with cloud applications. Assessing the codebase alone provides limited insight into how cloud applications work.
Accumulated misconfigurations increase the application’s vulnerability risk.
Related content: Read our guide to cloud DevOps
SAST vs. Other Security Methods
SAST vs. DAST
DAST encompasses several techniques and tools for identifying vulnerabilities in active applications, usually web applications. DAST is a black box testing method, so there is no knowledge of the application’s code base. DAST tools feed or inject malicious or flawed data into the tested software.
DAST solutions often require more security expertise and take longer to run tests than a SAST tool. DAST does not involve conventional scanning methods, so measuring the test’s performance using standard metrics like lines per second is impossible. The solution only provides inputs or attempts actions at specific junctures in the app’s operation.
Another major difference is that SAST tools often generate many false positives. On the other hand, DAST tools usually have a low false-positive rate because they use sophisticated test criteria focussing on real, discoverable vulnerabilities.
SAST vs. IAST
Interactive Application Security Testing (IAST) combines some of the top features of DAST and SAST. Its purpose is to provide application security testing within the application, typically during the development phase. When configured correctly, IAST solutions offer the following capabilities:
- Accessing all the code in an application.
- Collecting runtime application information about data flow and control.
- Accessing configuration data.
- Monitoring network traffic.
- Accessing application components such as data, libraries, and frameworks in dependencies at the back end.
Compared to SAST and DAST, IAST processes more code, provides more reliable results, and generates a more comprehensive view of applications and their environments to identify security vulnerabilities.
IAST solutions can perform code scans like SAST products, allowing them to discover vulnerabilities quickly and support early code fixes. Developers can address coding issues sooner to avoid higher costs and delays.
However, the main problem with IAST is that it uses software agents. The instrumentation code snippets are usually small and generally harmless, but they can affect the behavior of applications and slow down performance. Applying IAST tools can cause problems for highly performance-sensitive apps—a long-term concern for agents.
SAST vs. SCA
Software Configuration Analysis (SCA) is an application security technique that enables developers to track and analyze the open source components introduced into a shared project. SCA solutions scan dependencies to identify security vulnerabilities.
While SAST is best suited for testing code during the writing stage, SCA can effectively analyze the open source software components and dependencies used in the application. Both methods allow organizations to address security issues frequently and early in the SDLC.
An approach that combines the two allows organizations to discover more vulnerabilities, given that each tool focuses on different types of threats. SCA offers a dynamic security testing approach to complement the static SAST approach, covering open source and native code.
Protecting the Software Supply Chain with Aqua Security
To combat the supply chain problem, security teams need to bolster collaboration with DevOps teams and implement automation of security within development processes. Aqua recommends adopting new security solutions that are designed to secure the software development process against this new wave of sophisticated attacks.
Aqua identified three primary areas of risk that companies should understand and address to improve software supply chain security:
- Vulnerable Packages Usage
- Compromised Pipeline Tools
- Code/Artifact Integrity