Navigating the World of SAST: What is Static Application Security Testing?

Static application security testing (SAST) is a core component of robust DevSecOps. By analyzing source code, bytecode, or binaries to pinpoint potential vulnerabilities before your application becomes live, you can significantly reduce the attack surface of your applications.

This white-box methodology is best applied early and throughout the software development lifecycle to reduce remediation costs and mitigate risks. But what is happening with SAST, where and why should you be using it, and what limitations mean you need to use other types of security testing? Let’s go through that here so you know where this technique fits in your security deployment.

What is SAST?

Static application security testing is a white-box method of finding security vulnerabilities in software by examining its source code while it's not running. SAST tools have complete visibility into the application's source code, enabling them to conduct deep security analysis. According to our recent State of Software Quality survey, static analysis security tools  are being used by just 42% of development teams. 

SAST scans analyze your source code, looking for patterns that match known security flaws. It traces how data moves through the application, pinpointing potential points where malicious input could be exploited. The tool then reports any suspicious patterns, like potential SQL injection risks or buffer overflow possibilities. Many SAST tools then offer suggestions on how to fix the identified vulnerabilities, streamlining the remediation process for developers.

Under the hood, SAST tools often use a combination of control-flow graphs (CFGs) and abstract syntax trees (ASTs). 

The AST provides the underlying structure of the code. An AST is a tree-like representation of your code's structure, breaking it into syntactic elements (like function calls, variable assignments, conditional statements, etc.). SAST tools analyze the AST to understand the relationships between different code elements. This helps to identify potential paths that malicious data could take and to trace how the application might process that data.

The CFG adds the crucial layer of understanding how the code will execute, including potential conditional behavior and looping possibilities. A CFG is a graphical representation of all the paths execution could take through your code. Its nodes represent blocks of code, and its edges depict potential jumps between blocks (like loops or conditional branches). SAST tools use CFGs to:

• Pinpoint Vulnerabilities: The tool looks for patterns in the CFG that correspond to known vulnerabilities, like a branch leading to unsanitized user input flowing into a database query.
  
  
• Assess False Positives: CFGs help SAST tools understand the context of potential flaws, reducing the chance of reporting harmless code segments as vulnerable.

Why You Should Use SAST in Your Deployment Pipeline

SAST offers a crucial layer of proactive security within modern software development lifecycles (SDLCs). By integrating SAST into your deployment pipeline, you can catch vulnerabilities at the source. SAST operates directly on the source code, enabling it to discover security flaws before they become exploitable problems in production. Since remediation costs escalate drastically the later issues are found, this significantly benefits efficiency and long-term security posture.

SAST goes beyond simple pattern matching. SAST is highly effective in spotting OWASP's Top 10 flaws like broken access control (A01) and SQL injection (A03). Let’s say you had the following code in your application:

def update_user_profile(request):
    userID = request.GET.get('userID') 
    # ... fetch profile data
    # ... update profile based on request 

A SAST tool would spot several concerns:

• Implicit Trust: It assumes the userID belongs to the currently logged-in user.
  
  
• Missing Authorization: No explicit check to confirm if the current user is authorized to edit the profile corresponding to userID. This opens the door to unauthorized profile changes.

Broken access control is tricky to catch with automated tools alone, but SAST offers crucial support. SAST analyzes how your application implements authorization controls (what various roles/users may or may not do).  It looks for conditional checks, function definitions, and access management structures within the code.

One core SAST focus is spotting areas where authorization checks are absent or bypassed. Think code paths leading to sensitive actions that lack a "should this user be allowed here?" step. Even if checks exist, SAST will highlight issues like:

• Overly permissive logic or role/permission definitions granting unintended access.
  
  
• Authorization decisions relying on easily manipulated client-side data.

SAST can also flag Insecure Direct Object References (IDORs), a classic BAC issue. SAST flags patterns where object IDs (e.g., user profile IDs, document IDs) are taken from input without verifying the user has ownership or access rights to that object.

For SQL injection, you might have issues with this type of pattern:

String username = request.getParameter("username"); 
String query = "SELECT * FROM users WHERE username = '" + username + "'";
// ... execute the query 

A static application security testing

 tool would spot the problems here, highlighting:

• User input (username) flows directly to the query string.
  
  
• String concatenation creates a vulnerable injection point.
  
  
• No evidence of input sanitization or parameterized queries.

SAST tools have an extensive library of 'known bad' coding patterns for SQL injection.  Using taint analysis, a clear vulnerability is reported when they find input from a dubious source (like HTTP parameters) flowing into queries that match this pattern.

Many SAST tools understand common database frameworks and libraries (e.g., Hibernate, Entity Framework). This lets them tailor the analysis for how queries are built, helping avoid false positives and improving the accuracy of SQL injection detection.

They can also find subtle logic errors, such as misunderstood API uses, dangerous configurations, and unsafe data flows (leading to deserialization attacks). These will often escape standard testing but are prime SAST targets.

Static application security testing should be embedded as an automated step within continuous integration pipelines for optimal results. Developers get valuable feedback early and often, fostering proactive remediation rather than costly fixes post-deployment. When SAST tools generate outdated reports, re-scans throughout the SDLC become essential to avoid shipping new code with potentially overlooked vulnerabilities.

The Key Considerations of SAST

Despite its advantages, SAST possesses inherent limitations. Code analyzed without its runtime context naturally produces false positives–identifying issues that aren't exploitable in the specific application.

Consequently, experienced security engineers should establish processes for triaging alerts reported by SAST tools. Prioritization should be driven by contextual evaluation, determining the genuine exploitability and the associated risk to the business.

Therefore, these considerations are vital:

• SAST is a part of a holistic approach: Do not rely on SAST as your sole security testing strategy. SAST's strength lies in static analysis; it cannot replicate the live conditions of a running application. To address runtime vulnerabilities, configuration weaknesses, and zero-day exploits, complement SAST with techniques like Dynamic Application Security Testing (DAST), Interactive Application Security Testing (IAST), and regular penetration testing.
  
  
• You need an in-depth understanding of SAST outputs: While SAST is invaluable in uncovering code-level flaws, interpreting its output requires expertise. Many tools suffer from false-positive rates. Security engineers must be able to sift through reported issues, validate their true exploitability based on the application's architecture, and prioritize fixes accordingly. Failure to do so can lead to wasted resources and misaligned security efforts.

But, SAST will become more and more crucial in the testing pipeline. When evaluating SAST tools, you want to consider the following:

• Developer Empowerment: Modern SAST tools go beyond reporting flaws; they can play a pivotal role in secure coding education. Look for solutions that seamlessly integrate with IDEs, offering developers immediate suggestions and remediation guidance. This proactive approach empowers developers to write secure code from the onset, reducing the likelihood of recurring vulnerability patterns.
  
  
• The Value of Customization: Predefined rulesets within SAST tools are invaluable but rarely cover every nuance of your unique codebase. Organizations should invest time refining those rulesets, creating custom patterns to match internal coding standards, and identifying organization-specific vulnerabilities. This fine-tuning minimizes false positives and improves the tool's overall effectiveness.
  
  
• Tool Maintenance and Overhead: SAST can introduce some overhead into development pipelines, particularly for large codebases. Monitor scan times and optimize tool configurations to avoid adversely impacting developer velocity. Additionally, be prepared for the ongoing maintenance of tool integrations and the constant refinement of security rulesets as your application and technological landscape evolve.

Using Codacy Security As Your Security Pipeline

SAST plays a vital role in modern application security (AppSec), empowering you to locate vulnerabilities earlier, where fixing them is more straightforward and less expensive. In the constant battle against malicious actors, SAST proactively strengthens your application's armor.

Static application security testing isn't a silver bullet: Security success involves a layered strategy. Pair SAST with DAST (Dynamic Application Security Testing), SCA for supply chain security, and penetration testing for robust risk mitigation.

Codacy Security excels in these areas, giving you an end-to-end security posture, providing deep code analysis, prioritizing developer support, and promoting flexible adaptation for maximum impact. By understanding the strengths and appropriate context of SAST, you move decisively towards a more secure software future.