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Navigating Application Security Testing (AST): Methods and Best Practices

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The application layer remains a prime target for cyberattacks. In fact, nearly 50% of data breaches over the past several years originated at the web application layer. Why? The simplest explanation is humans make mistakes—and programmers are humans. A minor misconfiguration or lack of proper input validation in code can create an opportunity for attackers to exploit.

Therefore, it is essential to identify application security flaws early in the software development lifecycle (SDLC) to ensure that vulnerabilities in the application are remediated or mitigated before they are exploited.

Application Security Testing (AST) streamlines the process of identifying and remedying security flaws, thereby reducing the risk of security vulnerabilities. Therefore, a solid AST framework is critical for safeguarding the security and availability of software applications.

In this article, we delve into methods and best practices for implementing AST within your organization to ensure robust protection against potential threats.

What Is Application Security Testing?

Application security testing (AST) is the systematic process of identifying and evaluating security vulnerabilities within an application's code, design, and functionality. These methodologies and tools empower software development teams to create more secure source code with enhanced security measures, safeguarding applications from external and internal threats.

An effective AST program is an ongoing effort that utilizes a combination of tools, services, and human expertise to ensure that the deployed software is in compliance with predefined security criteria. 

Such a program should:

  • Reduce vulnerabilities: Actively work to decrease the number of vulnerabilities in applications released by the organization.

  • Address root causes: Identify and tackle underlying causes of vulnerabilities to prevent their recurrence in the future.

  • Enhance insight: Provide comprehensive insights into the organization's application security posture.

  • Mitigate impact: Lessen the potential impact of undetected or unassessed vulnerabilities.

Why Is Application Security Testing Important?

Software development teams today are not taking application security for granted. According to Codacy's 2024 State of Software Quality survey, 84% of development teams conduct regular security audits, and 88.4% have a dedicated security team or person. Application Security Testing (AST) plays a crucial role in mitigating security risks and ensuring compliance with regulatory standards. Here's why AST is important:

  • Identification of vulnerabilities: Through lack of experience, oversight, or carelessness, software developers can unintentionally introduce vulnerabilities like SQL injection, cross-site scripting (XSS), and broken authentication flaws into the software, making it a prime target for cyber attacks. AST reviews an application's code, design, and functionality to pinpoint these vulnerabilities for fixing before attackers exploit them.

  • Cost reduction: Dealing with security breaches after deployment can be financially crippling, leading to legal expenses, regulatory fines, remediation costs, and loss of reputation. Organizations can avoid the hefty expenses associated with security incidents and breaches by identifying and addressing vulnerabilities early through AST.

  • Compliance assurance: Various industries have regulatory requirements concerning application security, such as PCI DSS, HIPAA, and GDPR. AST helps organizations ensure compliance by detecting and rectifying security vulnerabilities, safeguarding sensitive data, and maintaining regulatory adherence.

Types of Automated Application Security Testing Methods 

With the rapid pace of software development, identifying vulnerabilities in a large code base amidst frequent deployments can be challenging. Automated AST tools can significantly simplify the process of identifying vulnerabilities in code. Let's review some of them.

1. Static Application Security Testing (SAST)

SAST is a "white-box" testing method that analyzes an application's source code, bytecode, or binary code for security vulnerabilities without executing it. SAST tools use static analysis techniques to scan the codebase for coding and design flaws that could allow for a security attack, such as insecure coding practices, hardcoded credentials, SQL injection, XSS, and other OWASP Top 10 vulnerabilities.

String username = userInput;
String password = "password123";
String query = "SELECT * FROM users WHERE username='" + username + "' AND password='" + password + "'";

In this code snippet, the userInput variable is directly concatenated into the SQL query string without any validation or sanitization. This code is vulnerable to SQL injection attacks, where an attacker can manipulate the userInput variable to inject malicious SQL code and potentially gain unauthorized access to the database. 

A SAST tool can point out this error along with the line in which it occurred, helping the developer correct it.

Strengths of SAST

  • Early detection: SAST operates early in the SDLC, catching vulnerabilities at the code level before deployment.

  • White-box testing: Being a "white-box" testing method, SAST has full access to the source code, enabling comprehensive analysis.

  • Line-of-code feedback: SAST tools offer developers real-time feedback and line-of-code navigation during the coding process, enabling them to address issues before advancing to the next phase of the SDLC.

Weaknesses of SAST

  • False positives: SAST tools may generate false positives, requiring manual verification and potentially delaying development.

  • Limited scope: SAST tools are not capable of identifying vulnerabilities outside the code or issues that only occur during runtime. For instance, vulnerabilities within a third-party API would elude detection by SAST tools and would require Dynamic Application Security Testing (DAST).

2. Dynamic Application Security Testing (DAST)

DAST is a type of application security testing that is used to detect security vulnerabilities by simulating attacks against an application in its running state. DAST examines the application as a “black box,” meaning it does not require access to the application's source code. Instead, it interacts with the application like a malicious user would through its front-end or external interfaces, such as HTTP requests. 

DAST typically employs a crawler or spidering mechanism to navigate through the application's functionalities, injecting malicious payloads and inputs into the application's input fields, URLs, and request parameters to test how the application handles and processes these inputs. After this simulation, DAST tools look for indications of successful attacks, such as error messages, unexpected behavior, or unauthorized access.

DAST can detect a Cross-Site Scripting (XSS) vulnerability in the following HTML form:

<form action="login.php" method="post">
    <input type="text" name="username" value="<script>alert('XSS');</script>">
    <input type="password" name="password">
    <input type="submit" value="Login">

Here, DAST tools would simulate an attack by injecting a malicious script into the username input field, such as <script>alert('XSS');</script>. If the application fails to sanitize or escape this input properly, it would render the script and execute it in the context of other users' browsers, leading to an XSS vulnerability.

DAST tools often maintain databases of known vulnerabilities and attack patterns, allowing them to compare the application's behavior against known attack signatures and patterns to identify potential security issues. 

Strengths of DAST

  • Real-world simulation: By interacting with the application in its running state, DAST provides insights into how an application will behave in real-world malicious conditions.

  • Black-box testing: DAST’s "black-box" testing method makes it programming language agnostic and suitable for testing third-party or legacy applications.

  • Detection of runtime vulnerabilities: DAST detects vulnerabilities that may only manifest during runtime, such as input validation failures and configuration errors.

Weaknesses of DAST

  • Black-box approach: Because DAST does not have access to the source code, it cannot pinpoint the exact location or root cause of vulnerabilities.

  • Limited context: While DAST is good for simulating real-world attacks, it cannot be used in real time (most DAST tools take several hours or days to completely scan an application). This is where Interactive Application Security Testing (IAST) helps.

3. Interactive Application Security Testing (IAST)

IAST is an approach to application security testing that combines the advantages of both SAST (static analysis of code) and DAST (testing of the running application) to provide real-time security analysis during an application's runtime.

Unlike traditional testing methods that analyze code statically (SAST) or interact with the running application externally (DAST), IAST continuously monitors the application's internal behavior during “real user” interactions. It focuses on detecting vulnerabilities based on how the application processes user input rather than waiting for scheduled scans. 

Imagine an e-commerce application that offers a single-use discount coupon to new users upon signing up. 

public class CouponValidator {
    public boolean validateCoupon(String couponCode, boolean isNewUser) {
        if (isNewUser && isValidCouponCode(couponCode)) {
            return true; // Coupon is valid for new users
        } else {
            return false; // Coupon is invalid

    private boolean isValidCouponCode(String couponCode) {
        // Logic to check if the coupon code is valid

        return true;

In this code snippet, the CouponValidator class validates a coupon code (couponCode) based on whether the user is new (isNewUser) and if the coupon code is valid.

During real-time usage, an IAST tool injects a sensor into the running application to monitor the application's behavior and interactions, including coupon code validations. If an existing user successfully applies and benefits from the new user discount coupon, the IAST tool would detect this anomaly. It would raise an alert or report indicating the business logic failure or misconfiguration, allowing developers to investigate and rectify the issue promptly.

Strengths of IAST

  • Real-time detection: IAST detects vulnerabilities as they occur during user interactions, providing faster remediation.

  • Context-specific alerts: IAST can pinpoint the exact location of the vulnerability within the code, along with the user input that triggered it.

  • Focus on user input: IAST excels at finding vulnerabilities related to how the application handles user data, business logic, and validation flaws.

Weaknesses of IAST

  • Reliance on user interactions: IAST is interactive and requires actual user activity to identify vulnerabilities, which can be limited in early development stages.

  • Integration complexity: Setting up IAST might involve instrumenting the application code with sensors, requiring some development effort.

4. Software Composition Analysis (SCA)

SCA involves scanning an application to find all the software components from which it is made. This analysis includes both open-source code and, in some cases, third-party components from vendors.

Once SCA identifies these components, it checks them against databases of known security vulnerabilities to discover if any of the libraries have weaknesses that attackers could exploit.

SCA can also identify potential licensing issues with the open-source components in your application. This ensures you're compliant with the license terms and avoids legal complications.

Beyond security and licensing, SCA considers operational risks associated with the components and libraries. This includes assessing the stability, maintenance status, community support, and update frequency of the libraries to evaluate potential risks to the application's functionality and reliability.

Best Practices for Application Security Testing 

Cyberattacks are constantly evolving. With increasing reliance on web applications, ensuring application security is more important than ever before. Here's how to elevate your application security testing strategy to safeguard sensitive data and minimize the risk of costly breaches.

  1. Shift security left: Integrate security testing throughout the SDLC, not just at the end. DevSecOps practices encourage incorporating various application security testing tools into specific development phases. This allows for early vulnerability detection and correction, saving time and resources.

  2. Go beyond external applications: Don't just focus on externally facing applications. Internal applications can also be vulnerable to attacks. Phishing campaigns targeting employees or unauthorized access to sensitive information due to weak access controls are some potential threats internal applications face.

  3. Lean on human experience: While automation plays a vital role, certain vulnerabilities require human experience to be accurately identified and verified. Business logic flaws or cryptographic misuse are areas where a tester and code reviewer's understanding of the application's functionality and proper security practices can be invaluable.

  4. Combine testing methods: A holistic security approach utilizes different testing methods for comprehensive coverage. SAST analyzes code for vulnerabilities early on. DAST simulates real-world attacks against the running application. IAST monitors the application's internal behavior during user interactions to detect vulnerabilities in real time.

  5. Integrate AST into CI/CD:  Streamline your workflow by integrating automated security testing tools directly into your Continuous Integration and Continuous Delivery (CI/CD) pipeline. This allows for automated vulnerability detection and remediation as part of the development process.

  6. Test frequently: Implement a proactive testing schedule to conduct security tests frequently, especially after code changes, updates, or new feature implementations. Regular testing helps identify and address vulnerabilities promptly, reducing the risk of security breaches.
  7. Monitor third-party code: The Log4j vulnerabilitya critical security flaw that allowed remote attackers to execute arbitrary code on affected systems via specially crafted log messagesis a stark reminder of the risks associated with third-party code. Regularly monitor your dependencies for known vulnerabilities and keep them updated.

  8. Conduct regular penetration testing: Penetration testing, or pen testing, is a proactive security measure that involves simulating real-world attacks on your applications and infrastructure to identify vulnerabilities before malicious actors exploit them. Penetration tests uncover vulnerabilities that may not be detected by automated tools or traditional security measures.

  9. Perform Red Team security exercises: Red Team application security exercises simulate real-world cyber attacks to evaluate an organization's application defense capabilities. These exercises go beyond identifying known vulnerabilities (as done by AST) and assess the effectiveness of security measures against sophisticated attack scenarios. Red Team exercises provide valuable insights into the application's resilience against targeted attacks and help organizations enhance their overall security posture.

Enhance Your Application Security Testing Workflow With Codacy

A solid application security testing program requires a strategic approach that integrates best practices and utilizes the right tools. Selecting the right AST tools can significantly enhance your application security workflow.
Codacy Security offers access to static application security testing across over 40 programming languages, Software Composition Analysis (SCA) for dependency management, and automated security code reviews. This comprehensive approach empowers your developers to write and ship secure code faster.
Take your application security testing to the next level by signing up for a free trial today


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