What is Security Testing? Complete Guide to Application Security

Parul Dhingra13+ Years ExperienceHire Me

Senior Quality Analyst

Updated: 1/22/2025

Security testing is a software testing practice that identifies vulnerabilities, weaknesses, and potential attack vectors in applications. The goal is straightforward: find security flaws before malicious actors do.

Unlike functional testing that validates features work correctly, security testing validates that applications resist attacks, protect sensitive data, and maintain integrity under hostile conditions.

This guide covers practical security testing approaches, from automated scanning to manual penetration testing, with actionable strategies for integrating security into your development workflow.

Understanding Security Testing Fundamentals

Security testing evaluates applications against six core principles:

Confidentiality ensures sensitive data remains accessible only to authorized users. Testing validates that encryption, access controls, and data handling prevent unauthorized disclosure.

Integrity confirms data remains accurate and unaltered during storage and transmission. Testing checks for vulnerabilities that could allow unauthorized modifications.

Availability verifies the application remains accessible to legitimate users. Testing includes resilience against denial-of-service attacks and resource exhaustion.

Authentication validates that user identity verification works correctly. Testing examines login mechanisms, password policies, multi-factor authentication, and session management.

Authorization confirms users can only access resources they have permission for. Testing validates role-based access controls and privilege boundaries.

Non-repudiation ensures users cannot deny their actions. Testing validates audit logging, transaction records, and accountability mechanisms.

Why Security Testing Matters

The consequences of security failures are severe:

• Financial impact: Data breaches result in direct costs (incident response, legal fees, regulatory fines) and indirect costs (lost business, remediation)
• Reputation damage: Security incidents erode customer trust and brand value
• Regulatory compliance: Industries like healthcare (HIPAA), finance (PCI-DSS), and any organization handling EU citizen data (GDPR) face mandatory security requirements
• Business continuity: Successful attacks can disrupt operations for days or weeks

Security testing shifts the cost equation. Finding vulnerabilities during development costs a fraction of addressing them after a breach.

Security Testing vs Functional Testing

Both testing types are essential. Functional tests ensure the application works. Security tests ensure it does not break under attack.

Types of Security Testing

Security testing encompasses several distinct approaches, each addressing different aspects of application security.

Overview of Testing Types

Static Application Security Testing (SAST) analyzes source code without executing the application. It finds vulnerabilities in code patterns, configuration files, and dependencies.

Dynamic Application Security Testing (DAST) tests the running application by sending malicious inputs and observing responses. It simulates external attacks.

Interactive Application Security Testing (IAST) combines SAST and DAST by instrumenting the application to monitor behavior during testing.

Penetration Testing involves security professionals manually attempting to exploit vulnerabilities, simulating real-world attack scenarios.

Vulnerability Scanning uses automated tools to identify known vulnerabilities in systems, networks, and applications.

Security Audits are systematic reviews of security policies, configurations, and controls against established standards.

Each approach has strengths and limitations. Effective security programs combine multiple methods for comprehensive coverage.

Static Application Security Testing (SAST)

SAST tools analyze source code, bytecode, or binaries to identify security vulnerabilities without running the application. This approach is also called "white-box testing" because it examines the internal structure of the code.

How SAST Works

SAST tools perform several types of analysis:

Data Flow Analysis tracks how data moves through the application, identifying where untrusted input reaches sensitive operations without proper validation.

Control Flow Analysis examines the paths code execution can take, finding conditions that could lead to security issues.

Pattern Matching compares code against known vulnerable patterns, such as SQL concatenation or unsafe deserialization.

Configuration Analysis checks configuration files for insecure settings like debug modes enabled or weak encryption algorithms specified.

SAST Strengths

• Early detection: Finds vulnerabilities as code is written, before deployment
• Complete coverage: Analyzes all code paths, including error handlers rarely exercised
• Specific remediation: Points to exact line numbers and code patterns causing issues
• Scalable: Automated analysis handles large codebases efficiently
• Language-specific: Understands language idioms and framework conventions

SAST Limitations

• False positives: Reports issues that are not actually exploitable, requiring manual review
• No runtime context: Cannot detect configuration issues or vulnerabilities that emerge only at runtime
• Build integration required: Needs access to source code and build environment
• Language/framework support: Coverage varies by programming language and framework

SAST Tools

SAST Best Practices

Integrate into development workflow: Run SAST on every commit or pull request to catch issues immediately.

Tune rules to reduce noise: Disable rules that generate excessive false positives for your codebase. A tool that produces too many false alarms gets ignored.

Prioritize findings: Focus on high-severity issues in critical code paths first. Not all vulnerabilities carry equal risk.

Track trends over time: Monitor vulnerability counts across releases to ensure security is improving, not degrading.

Dynamic Application Security Testing (DAST)

DAST tests applications from the outside while they are running, simulating attacks an external attacker might perform. This approach is called "black-box testing" because the tool does not see the internal code.

How DAST Works

DAST tools follow a general process:

1. Crawling/Spidering: Discover application pages, forms, and endpoints by following links and analyzing responses
2. Attack Simulation: Send malicious payloads to discovered inputs (forms, URL parameters, headers, cookies)
3. Response Analysis: Examine application responses for signs of vulnerabilities (error messages, unexpected behavior, data leakage)
4. Reporting: Document discovered vulnerabilities with reproduction steps

DAST Strengths

• Runtime context: Tests the actual deployed application with real configurations
• Technology agnostic: Does not matter what language or framework the application uses
• Low false positives: Confirms vulnerabilities are actually exploitable
• No source code required: Can test third-party applications and APIs
• Realistic testing: Simulates actual attack scenarios

DAST Limitations

• Limited coverage: Only tests paths the crawler discovers; authenticated areas need configuration
• No code-level details: Reports that a vulnerability exists but not exactly where in the code
• Slower execution: Requires a running application and network communication
• Environment required: Needs a test environment that mirrors production

DAST Tools

DAST Best Practices

Configure authentication: Ensure the scanner can access authenticated areas. Most vulnerabilities hide behind login screens.

Use a dedicated test environment: Never run DAST against production without explicit authorization and safeguards. Scans can cause data corruption or service disruption.

Provide a starting point: Give the scanner a sitemap or list of URLs to ensure complete coverage.

Schedule regular scans: Run DAST weekly or before each release to catch new vulnerabilities.

Penetration Testing

Penetration testing (pen testing) goes beyond automated scanning. Security professionals manually attempt to exploit vulnerabilities, chaining multiple weaknesses to demonstrate real-world attack impact.

Penetration Testing Approaches

Black Box Testing: Testers have no prior knowledge of the system. They approach it as an external attacker would, discovering information and vulnerabilities through reconnaissance and testing.

White Box Testing: Testers have full access to source code, architecture documentation, and system credentials. This enables thorough testing of specific components.

Gray Box Testing: Testers have partial knowledge, perhaps user-level credentials and basic architecture information. This balances realism with efficiency.

Penetration Testing Phases

1. Planning and Reconnaissance: Define scope, gather information about targets, identify potential attack surfaces
2. Scanning: Use automated tools to discover vulnerabilities and map the attack surface
3. Exploitation: Attempt to exploit discovered vulnerabilities to gain access or extract data
4. Post-Exploitation: Once access is gained, explore what an attacker could achieve (lateral movement, privilege escalation, data access)
5. Reporting: Document findings with severity ratings, evidence, and remediation recommendations

When to Conduct Penetration Testing

• Before major releases or significant architectural changes
• After implementing new security controls to validate effectiveness
• Following a security incident to assess scope and residual risk
• To meet compliance requirements (PCI-DSS requires annual pen tests)
• When onboarding new third-party integrations

Penetration Testing vs Vulnerability Scanning

Note: Penetration testing and vulnerability scanning complement each other. Scanning provides broad coverage efficiently. Pen testing provides depth and validates real-world exploitability.

Vulnerability Scanning

Vulnerability scanning uses automated tools to identify known security weaknesses in systems, networks, and applications. Scanners maintain databases of known vulnerabilities and check targets against them.

Types of Vulnerability Scanners

Network Vulnerability Scanners examine network infrastructure: servers, firewalls, routers, and network services. They identify missing patches, misconfigurations, and exposed services.

Web Application Scanners test web applications for common vulnerabilities like SQL injection, XSS, and insecure configurations.

Database Scanners check database systems for vulnerabilities, weak configurations, and excessive permissions.

Container Scanners analyze container images for vulnerable dependencies, misconfigurations, and compliance issues.

Dependency Scanners examine application dependencies (npm packages, Python libraries, etc.) for known vulnerabilities.

Vulnerability Scanning Tools

Scanning Best Practices

Scan regularly: Weekly scans catch new vulnerabilities as they are disclosed.

Authenticate scans: Authenticated scanning discovers more vulnerabilities than unauthenticated scans.

Prioritize by context: A critical vulnerability in an internal tool differs in risk from the same vulnerability in a public-facing application.

Track remediation: Vulnerability management is not just finding issues but ensuring they get fixed.

Validate findings: Some scanner findings are false positives. Verify before investing remediation effort.

The OWASP Top 10

The Open Web Application Security Project (OWASP) Top 10 represents the most critical security risks to web applications. Updated periodically based on real-world data, it serves as the industry baseline for web security testing.

OWASP Top 10 (2021 Edition)

A01: Broken Access Control - Users can act outside their intended permissions. Examples include accessing other users' data, modifying access rights, or bypassing authorization checks.

Testing approach: Verify access controls at every function. Test horizontal privilege escalation (accessing another user's data) and vertical escalation (accessing admin functions as a regular user).

A02: Cryptographic Failures - Weaknesses in cryptography that expose sensitive data. Includes using weak algorithms, improper key management, and transmitting data in clear text.

Testing approach: Check for HTTPS enforcement, examine encryption algorithms in use, verify sensitive data is encrypted at rest and in transit.

A03: Injection - Untrusted data sent to an interpreter as part of a command or query. SQL injection remains common, but also includes NoSQL, OS command, LDAP, and expression language injection.

Testing approach: Test all input points with payloads designed to break out of the intended context. Use both automated scanners and manual testing with application-specific payloads.

A04: Insecure Design - Missing or ineffective security controls at the design level. No amount of implementation fixes can address fundamental design flaws.

Testing approach: Review threat models, validate security requirements exist for each feature, check for defense-in-depth patterns.

A05: Security Misconfiguration - Insecure default configurations, incomplete configurations, open cloud storage, misconfigured HTTP headers, or verbose error messages.

Testing approach: Review configurations against security baselines. Check for unnecessary features enabled, default credentials, and information disclosure.

A06: Vulnerable and Outdated Components - Using libraries, frameworks, or other software with known vulnerabilities.

Testing approach: Maintain a software bill of materials (SBOM). Use dependency scanning tools to identify vulnerable components.

A07: Identification and Authentication Failures - Weaknesses in authentication and session management. Includes weak passwords, credential stuffing vulnerabilities, and session fixation.

Testing approach: Test password policies, brute force protections, session handling, and multi-factor authentication implementations.

A08: Software and Data Integrity Failures - Code and infrastructure that does not protect against integrity violations. Includes insecure CI/CD pipelines and auto-update mechanisms without verification.

Testing approach: Review code signing, verify update mechanisms check integrity, examine CI/CD pipeline security.

A09: Security Logging and Monitoring Failures - Insufficient logging, detection, monitoring, and response. Attackers rely on the lack of monitoring to achieve their objectives.

Testing approach: Verify security events are logged, logs are protected from tampering, and alerting mechanisms exist for suspicious activity.

A10: Server-Side Request Forgery (SSRF) - Applications that fetch remote resources without validating user-supplied URLs. Attackers can make the server send requests to unintended destinations.

Testing approach: Test URL input fields with internal addresses, cloud metadata endpoints, and other SSRF payloads.

Using OWASP Top 10 for Testing

The OWASP Top 10 should inform your security testing strategy:

1. Create test cases covering each risk category
2. Configure scanners to check for Top 10 vulnerabilities
3. Train developers on each risk and secure coding practices
4. Measure coverage - track what percentage of the Top 10 your testing addresses

Security Testing Tools

Integrated Security Testing Platforms

OWASP ZAP (Zed Attack Proxy): The most popular open-source web security scanner. Features include:

• Automated scanning and manual testing support
• Active scan for vulnerability detection
• Passive scan for reconnaissance
• Fuzzing capabilities
• API testing support
• CI/CD integration via automation API

Burp Suite: The industry-standard platform for web security testing. The Professional edition adds:

• Advanced scanning with proven accuracy
• Out-of-band application security testing
• Extensive extensibility via BApp Store
• Collaboration features for teams

Specialized Security Tools

Choosing the Right Tools

Consider these factors when selecting security testing tools:

Coverage needs: What types of applications do you test? Web apps, APIs, mobile, infrastructure?

Team expertise: Some tools require security expertise. Others are designed for developers.

Integration requirements: Does the tool integrate with your CI/CD pipeline, issue tracker, and existing workflow?

Budget: Open-source tools provide strong capabilities. Commercial tools add features, support, and reduced maintenance.

Compliance: Some regulations specify acceptable testing tools or methodologies.

When and How to Perform Security Testing

Security testing should occur throughout the development lifecycle, not just before release.

Security Testing Timing

During Development

• SAST on every commit or pull request
• IDE plugins that flag security issues as code is written
• Code review with security checklist

Before Merge

• SAST scan on the complete codebase
• Dependency vulnerability check
• Security-focused code review for sensitive changes

In Test Environment

• DAST scan against deployed application
• Integration testing of security controls
• Security regression tests

Before Release

• Comprehensive security scan
• Penetration testing for major releases
• Security signoff from stakeholders

In Production

• Continuous monitoring for attacks
• Regular vulnerability scanning
• Periodic penetration testing

Creating a Security Test Plan

A security test plan should address:

1. Scope: What applications, APIs, and infrastructure are in scope?
2. Objectives: What security requirements must be validated?
3. Approach: What combination of SAST, DAST, and manual testing?
4. Tools: Which tools will be used and why?
5. Environment: Where will testing occur? How will test data be handled?
6. Schedule: When will testing occur? What triggers additional testing?
7. Roles: Who performs testing? Who reviews results? Who owns remediation?
8. Reporting: How are vulnerabilities documented and tracked?

Security Testing in CI/CD Pipelines

Integrating security testing into CI/CD pipelines catches vulnerabilities early and prevents insecure code from reaching production.

Pipeline Integration Approaches

Shift-Left Security: Move security testing earlier in the pipeline:

Commit → SAST Scan → Build → DAST Scan → Deploy to Test → Security Tests → Deploy to Prod

Security Gates: Define pass/fail criteria for security checks:

• No critical or high severity vulnerabilities
• No new vulnerabilities introduced
• All security tests pass

Incremental Scanning: Scan only changed files on commits, full scans on merges or schedules.

Pipeline Configuration Considerations

Scan Time: Fast scans enable developer feedback. Schedule comprehensive scans for off-hours.

False Positive Management: Provide mechanisms to suppress false positives without hiding real issues.

Failure Handling: Decide whether security failures block deployment or generate alerts for review.

Secret Management: Ensure credentials for security tools are properly secured.

Example Pipeline Stages

1. Pre-Commit: IDE security plugins, pre-commit hooks for secrets detection
2. Build Stage: SAST analysis, dependency vulnerability check, container image scan
3. Test Stage: DAST scan, security unit tests, authentication/authorization tests
4. Pre-Production: Full security regression suite, compliance checks
5. Production: Continuous monitoring, scheduled vulnerability scans

Common Security Vulnerabilities and How to Test for Them

SQL Injection

What it is: Attackers insert SQL commands into input fields, which the application executes against the database.

Testing approach:

• Input SQL syntax characters: ' " ; --
• Try basic payloads: ' OR '1'='1 in login forms
• Use time-based detection: '; WAITFOR DELAY '0:0:5'--
• Automated tools like sqlmap for comprehensive testing

Prevention: Parameterized queries, prepared statements, input validation.

Cross-Site Scripting (XSS)

What it is: Attackers inject malicious scripts that execute in other users' browsers.

Testing approach:

• Inject script tags: <script>alert('XSS')</script>
• Try event handlers: <img src=x onerror=alert('XSS')>
• Test in different contexts: HTML, JavaScript, URL parameters, JSON responses
• Check for proper encoding in each output context

Prevention: Context-aware output encoding, Content Security Policy headers.

Authentication Weaknesses

What it is: Flaws allowing attackers to compromise credentials, sessions, or authentication mechanisms.

Testing approach:

• Attempt default credentials
• Test password complexity requirements
• Check for brute force protections
• Validate session token randomness and expiration
• Test "remember me" functionality
• Verify secure password reset process

Prevention: Strong password policies, account lockout, MFA, secure session management.

Authorization Flaws

What it is: Users accessing resources or functions beyond their permissions.

Testing approach:

• Access resources belonging to other users (IDOR - Insecure Direct Object References)
• Try admin functions as regular user
• Modify request parameters that indicate user role or permissions
• Test API endpoints directly, bypassing UI restrictions

Prevention: Server-side authorization checks on every request, principle of least privilege.

Security Misconfiguration

What it is: Insecure settings, unnecessary features, default accounts, or verbose errors.

Testing approach:

• Check for default credentials
• Review HTTP security headers
• Look for exposed admin interfaces
• Test for directory listing
• Check error messages for information disclosure

Prevention: Hardening guides, configuration management, regular security reviews.

Security Testing Best Practices

Integrate Security Early

Waiting until release to test security is expensive. Finding a SQL injection vulnerability on the day of launch creates pressure for hasty fixes or risky deployments.

• Include security requirements in user stories
• Train developers on secure coding
• Run automated security scans on every build
• Conduct threat modeling during design

Combine Automated and Manual Testing

Automation catches known vulnerability patterns at scale. Human testers find business logic flaws and chain vulnerabilities in ways scanners cannot.

• Use automated scanning for comprehensive coverage
• Reserve penetration testing for critical applications and major releases
• Conduct manual testing of authentication, authorization, and business logic

Prioritize Findings

Not all vulnerabilities are equal. Prioritize based on:

• Severity: What is the potential impact if exploited?
• Exploitability: How easy is it to exploit? Are public exploits available?
• Exposure: Is this in a public-facing system or internal tool?
• Data sensitivity: What data could be compromised?

Track and Measure

Security testing generates findings. Effective security programs track them to completion.

• Maintain a vulnerability backlog
• Set SLAs for remediation based on severity
• Track mean time to remediate
• Monitor vulnerability trends over time

Test the Full Stack

Modern applications span multiple layers. Each needs security testing:

• Frontend: XSS, sensitive data exposure, client-side controls
• APIs: Authentication, authorization, injection, rate limiting
• Backend: Server configuration, dependencies, database security
• Infrastructure: Network security, cloud configuration, container security
• Third-party integrations: Supply chain risks, API security

Challenges in Security Testing

False Positives and Alert Fatigue

Automated scanners report potential issues, not confirmed vulnerabilities. High false positive rates lead teams to ignore findings.

Solutions:

• Tune scanner rules to your application
• Triage findings before assigning to developers
• Use tools with better accuracy, even if slower
• Provide context with findings so developers can evaluate quickly

Coverage Limitations

No single tool or approach finds all vulnerabilities.

Solutions:

• Combine multiple testing methods (SAST + DAST + manual)
• Use different tools that find different vulnerability classes
• Ensure authenticated scanning for complete coverage
• Supplement with penetration testing

Keeping Up with Threats

New vulnerabilities and attack techniques emerge constantly.

Solutions:

• Subscribe to security advisories for your technology stack
• Update scanner signatures and rules regularly
• Include security training in professional development
• Participate in security communities

Testing Modern Architectures

Microservices, serverless, and cloud-native architectures create distributed attack surfaces.

Solutions:

• Test each service independently and as part of the whole
• Validate inter-service authentication and authorization
• Include infrastructure-as-code in security scanning
• Test cloud configurations and permissions

Resource Constraints

Security testing competes with other priorities. Teams may lack time, budget, or expertise.

Solutions:

• Automate routine security checks in CI/CD
• Focus manual testing on highest-risk areas
• Build security into the development process, not as an afterthought
• Use risk-based prioritization to maximize impact

Conclusion

Security testing is not optional. Applications that handle user data, process transactions, or connect to networks face continuous attack attempts. Finding vulnerabilities before attackers do is the only viable strategy.

Effective security testing combines multiple approaches:

• SAST catches vulnerabilities in code during development
• DAST validates the running application resists attacks
• Vulnerability scanning identifies known weaknesses across the stack
• Penetration testing demonstrates real-world exploitability

The OWASP Top 10 provides a baseline, but security testing should address risks specific to your application and threat model.

Integrate security testing into your CI/CD pipeline to catch issues early when they are cheapest to fix. Combine automated scanning with manual testing to balance coverage and depth. Track findings, prioritize by risk, and measure improvement over time.

Security is not a destination but an ongoing process. As applications evolve and new threats emerge, security testing must evolve with them.

Continue Reading

Frequently Asked Questions (FAQs) / People Also Ask (PAA)