SAST vs DAST: An Expert‘s Guide to Choosing the Right Application Security Testing Approach

Application security is more crucial than ever with web apps accounting for 43% of reported breaches. As your business digitally transforms adopting cloud and containers, your risks multiply. So rigorously testing apps using methods like SAST and DAST becomes critical.

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But between Static Application Security Testing (SAST) and Dynamic Application Security Testing (DAST), how do you pick the right approach? Both aim to uncover vulnerabilities after all.

Well as a cybersecurity expert with over 15 years of experience, I can tell you it depends! Each technique has unique strengths ideal for certain situations as we’ll see.

In this comprehensive guide, we’ll unpack:

  • What SAST and DAST are in-depth
  • How they work from a technical perspective
  • Key feature differences head-to-head
  • Real-world scenarios suited to SAST vs DAST
  • Using SAST and DAST together for robust security
  • Tips for choosing SAST vs DAST

Let‘s dig in!

What is SAST?

SAST or Static Application Security Testing analyzes application source code, configs and architecture diagrams for security flaws – before runtime.

By scrutinizing software internals for weaknesses, SAST takes a white-box approach. It enjoys full visibility into data flows, message calls, variable usage etc. across components. This allows uncovering vulnerabilities like:

  • SQL injections
  • Cross-site scripting
  • Memory leaks
  • Improper error handling

And more flaws arising from insecure code.

How SAST Security Testing Works

Modern SAST solutions like Checkmarx often include multiple engines for static analysis, software composition analysis, infrastructure-as-code scanning and more. But the core static testing workflow is:

  1. Parsing Code: The SAST engine decompiles application source code if needed and creates an intermediate representation for analysis.

  2. Data Flow Analysis: SAST traces data flows across app components to build a semantic understanding of the app’s logic and construction.

  3. Rule-based Analysis: The parsed code is then checked against a huge database of known vulnerabilities using customized rules. These evolving rules keep pace with new weakness classes and variants.

  4. Reporting: Finally, identified vulnerabilities are detailed out with risk grades and referenced code locations to support remediation.

Advanced SAST solutions also auto-confirm some identified issues using sophisticated logic. The whole process is automated using CI/CD integration.

Why Use SAST for Application Security?

SAST as an internally-focused white box testing method offers unique strengths:

  • Finds issues early during development when cheaper to fix
  • Scans all application code including rarely tested parts
  • Provides precise results with few false positives
  • Can be tuned to the tech stack and frameworks used
  • Integrates into coding sprints and CI/CD pipelines
  • Encourages developers to adopt secure coding best practices

These drive compelling security and efficiency benefits for custom-built applications.

What is DAST?

Unlike SAST, Dynamic Application Security Testing analyzes applications in a live running state – simulating how attackers see them.

DAST treats applications as black boxes. It scans fully assembled and deployed applications to uncover security holes like:

  • Cross-site scripting
  • SQL injections
  • Path traversal
  • Insecure configurations
  • Invalid session handling

And more flaws exposing confidentiality, integrity and availability.

How DAST Application Security Testing Works

DAST solutions like IBM AppScan focus strongly on automation. The high-level DAST flow is:

  1. Spider Crawl: DAST scans ingress pages and endpoints to discover exposed assets building an attack surface map. APIs, transactional flows etc. are learned.

  2. Attack Injection: Varied attacks like cross-site scripting, SQL injections, command injections etc. are fuzzer tested against the app to force unusual behavior.

  3. Vulnerability Analysis: Using sophisticated analytics, the app’s runtime responses are analyzed to detect security flaws, and security regression.

  4. Risk-based Reporting: Security issues finally show up on developer, business and compliance dashboards by risk levels and affected application functionalities.

DAST supports continuous scanning for DevSecOps via public cloud, private cloud, on-prem and hybrid options.

Why Use DAST Security Testing?

As black-box testing placing apps in a staging or production harness, DAST offers unique advantages:

  • Tests apps as users experience them exposing business risks
  • Catches issues that depend on run-time environments
  • Highlights insecure configurations and platform dependencies
  • Easy integration into both CI and post-deployment regression testing
  • No access to source code needed making it ideal for IaaS apps
  • Provides operational visibility critical for patch and host hardening prioritization

This makes DAST a versatile choice for staging and production application security testing.

SAST vs DAST Side-by-Side Comparison

While SAST and DAST serve the same goal of eliminating application vulnerabilities, they take very different approaches as we’ve seen.

Let‘s compare some key aspects head-to-head:

Parameter SAST DAST
Testing Style White box – internal code focused Black box – externally focused
Stage Tested Mainly development and code integration Later QA and pre-production staging
Visibility Full code visibility as white box No environment or code access as black box
Issue Coverage Strongest for pure coding flaws Catches more operational configuration issues
Team Impact Changes required from developers Limited disruption for app teams
False Positives Fewer due to internal context More common without internal insight

When SAST Security Testing Works Best:

  • For internally developed business applications
  • Need for very early and frequent security testing
  • Ability to scan regularly through integration with CI/CD pipelines
  • Full accessibility to source code for analysis
  • Benchmarking internal code quality versus security best practices

When to Rely on DAST Security Testing:

  • Validating security for external web apps or purchased software
  • Testing complicated configuration-dependent vulnerabilities
  • Paired with penetration testing to validate production readiness
  • Post-release regression testing of critical applications
  • Quick testing needed without waiting for new builds

So in summary, SAST takes an inward-facing developer-centric view focused on building apps securely. DAST looks outward validating externally visible security from an attacker mindset.

Using Both SAST and DAST for Comprehensive Application Security

While often positioned as competing choices, SAST and DAST can combine beautifully together!

They tackle complementary problem areas during application security testing. SAST finds more issues earlier from code, while DAST reveals deployment and configuration risks later. Using both ensures comprehensive assessment.

Let‘s see how to implement layered SAST plus DAST testing for end-to-end security.

SAST/DAST Layering in Practice

Typical steps are:

  • Run SAST scans natively during coding or through CI/CD integration
  • Use SAST for functional security testing confirming positives
  • Push vetted builds into QA systems for DAST scans
  • Establish DAST checks as part of staging testing gates before production
  • Treat DAST as final security verification safeguarding production
  • Remediate findings from both sources consistently

This cascading model测试 enables interlocking feedback loops:

sast dast application security testing together

Image source: GeekFlare

Developers gain visibility into coding risks plus operational impacts with tied findings. Testing teams handle validation before committing changes.

Together SAST and DAST provide comprehensive:

  • Code quality verification for developers
  • Infrastructure risk assessment for IT Ops
  • End-user mimicking validation for QA
  • Executive view of application security posture

This allows managing vulnerabilities across the entire application lifecycle.

SAST vs DAST: Expert Recommendations

With dozens of application security projects under my belt from design to deployment, here’s what I can tell you:

For Custom Application Development

  • Make SAST part of your secure coding checklist to build in security earlier
  • Integrate SAST wherever possible into your CI/CD pipeline through hooks offered by your provider
  • Establish SAST score standards and track them as code quality KPIs
  • Use integrated SAST to enforce uniform policies across distributed teams
  • Empower developers to be the first line of defense securing their code

For Application Operations

  • Use DAST SECURITY 测试 for final security verification before production deployment
  • Continuously test production apps using DAST to catch issues arising from configuration drift
  • Integrate next-gen Web Application Firewall (WAF) to production systems for run-time protection
  • Follow DevSecOps principles with security automation spanning across functional silos
  • Maintain always-on scanning with alerts aligned to your response workflows

For Leadership

  • Evaluate both SAST and DAST to align with internal development and deployment flows
  • Enhance risk visibility into application debt and technical lag across portfolios
  • Carefully assess findings to balance security investments versus modernization needs
  • Build unified dashboards for multi-layered insights into code quality and production vulnerabilities

When Getting Started

  • Kickstart using either SAST or DAST then expand to both for layered security over time
  • SAST offers faster setup while DAST provides quicker time-to-value from a security perspective
  • Integrate DAST with next-gen WAF like Imperva for run-time protection
  • For CI/CD adoption choose SAST aligned solutions like Checkmarx or Veracode
  • If cloud migration is planned ensure your vendor supports distributed teams with centralized management

Over time, plan towards continuous security assurance across build, deploy and run stages for resilient threat protection.

SAST vs DAST: Key Takeaways

Let’s recap the salient differences between SAST and DAST:

  • SAST offers internal code analysis from a developer lens
  • DAST validates externally visible security from an attack perspective
  • SAST finds more issues earlier in development
  • DAST reveals deployment and configuration weaknesses later
  • Use SAST for custom dev environments and compliance
  • Rely on DAST when no code access or for production security
  • Employ both SAST and DAST together for robust security

Now you have an expert perspective on picking SAST vs DAST approaches!

The key is using both tools as evolving application security demands cannot be met through just one testing method. Combining SAST and DAST testing establishes interlocked feedback loops so dev can remediate findings before ops inherits risk. This DevSecOps model places security assurance responsibility on those best positioned to fix issues early.

To conclude, SAST and DAST while competing solutions, actually work far better together! Using both across the SDLC helps identify more critical application flaws faster from both outside-in and inside-out. This allows holistic security visibility closing blindspots.

What questions do you still have on selecting either SAST or DAST security testing for your needs? Let me know in the comments!

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