SAST vs DAST: An In-Depth Technical Comparison for Application Security Testing

Applications have become prime targets for hackers as digital transformation accelerates across every industry. The shift to web and mobile apps has vastly increased attack surfaces available for exploitation. At the same time, software development practices like agile and DevOps emphasize speed over security, unintentionally introducing vulnerabilities.

The stakes for application security couldn‘t be higher. A recent study found the average cost of a data breach is now $4.35 million, a record high. Over 85% of breaches target web applications, exploiting vulnerabilities like injection attacks, authentication flaws, and misconfigurations.

To combat these risks, organizations must test applications for security continuously throughout the entire software development lifecycle (SDLC). Two proven methods for finding vulnerabilities during app testing are static application security testing (SAST) and dynamic application security testing (DAST).

This comprehensive, hands-on guide examines SAST and DAST in-depth. We‘ll compare how each works, strengths and limitations, optimal use cases, and how they can be combined for robust AppSec. Let’s dive in!

Understanding Static Application Security Testing

Static application testing, or SAST, analyzes application source code, binaries, and dependencies to uncover vulnerabilities without executing code. SAST solutions scan at rest before applications are running to provide insights early in development so flaws can be fixed quickly and cheaply.

According to Gartner, SAST tools are responsible for driving a 30% reduction in security defect resolution timelines and a 40% decrease in costs for remediation compared to finding bugs post-release. The earlier vulnerabilities can be detected, the better.

How SAST Works

SAST tools analyze source code using techniques like:

Control flow analysis – maps out all possible execution paths in a program to detect missing authorization checks, unhandled exceptions, and other logical flaws.
Data flow analysis – tracks how input data flows through an application to uncover potential misuse, like injection attacks.
Pattern matching – searches code for dangerous functions, insecure methods, blacklisted terms, and other undesirable patterns.
API modeling – understands legitimate use cases for libraries and APIs to detect potential misuse.

For example, static analysis could alert that user-supplied input is being passed unchecked into a dangerous method like Runtime.exec(), indicating a potential injection vulnerability.

SAST solutions can integrate directly into developer IDEs like Visual Studio, Eclipse, and IntelliJ for instant feedback on code flaws as developers write. SAST can also be incorporated into continuous integration and delivery (CI/CD) pipelines to automate security testing.

SAST Strengths

Analyzes source code, binaries, and dependencies for a wide range of vulnerabilities
Provides rapid feedback to developers early in SDLC when fixes are cheaper
Pinpoints the exact location of flaws in code to accelerate remediation
Significantly reduces susceptability to common attacks like XSS, SQLi, and buffer overflows
Low overhead scanning minimally impacts development speed

SAST Limitations

Only examines source code – cannot detect run-time configuration issues
Generates some false positives requiring manual verification
Advanced analysis like data flow modeling can slow down builds
Frequent tool updating required to maintain high detection rates
Limited vulnerability coverage for logical flaws and business logic

While extremely powerful, SAST testing also has blindspots that demand complementary approaches like dynamic analysis. Security teams should not rely solely on static testing to catch all issues.

Understanding Dynamic Application Security Testing

Dynamic application security testing, or DAST, analyzes applications while they are running to detect vulnerabilities missed by static analysis. DAST solutions simulate attacks against software by manipulating inputs and exploring execution paths to uncover runtime risks.

DAST scanner techniques include:

Fuzzing – injecting invalid, unexpected, or random data into parameters to crash apps and reveal failures in handling edge cases correctly.
Input manipulation – modifying API, URL, form, and other input values to uncover crashes, lack of validation, or system weaknesses.
Authentication testing – attempting common default credentials or exploring authorization bypasses.
API exploration – probing API endpoints to uncover unprotected access to data, functions, and resources.

For example, a DAST tool may remove authentication tokens or session IDs from requests to test if protected operations can still be accessed anonymously. If successful, the tool will warn the associated access control issue.

DAST solutions can generate and monitor traffic between all application components to detect vulnerabilities across an entire software ecosystem. DAST scanners simulate the perspective of an external attacker with no visibility into source code or internal workings.

DAST Strengths

Tests applications in dynamic production-like environments
Assesses attack surface exposed in real-world deployed usage
Detects functional and configuration issues missed by static scanning
Requires no source code access making it ideal for black box testing
Identifies weaknesses introduced at runtime like memory corruption

DAST Limitations

Can potentially crash or disrupt applications under test
High false positive rates requiring extensive manual verification
Ineffective at analyzing complex workflows and business logic
Provides limited detail on where code flaws originate
Resource intensive scanning can slow applications and CI/CD pipelines

Like SAST, DAST testing alone cannot provide complete test coverage. Organizations need layered testing and multiple perspectives to achieve robust security.

Comparing SAST and DAST Side-by-Side

Testing Method	SAST	DAST
Approach	White-box, internal analysis	Black-box, external attack perspective
Needs source code?	Yes	No
Analyzes	Source code, binaries, dependencies	Running application
When used?	Development and CI/CD pipelines	Staging, production
Techniques	Data flow, control flow, fuzzing, patterns	Fuzzing, input manipulation, auth testing
Finds	Coding flaws like XSS, injection, auth, encryption	Functional and configuration issues
Strengths	Early detection, actionable results, low overhead	Tests production deployments, no source required
Weaknesses	No runtime contexts, false positives	Disruptive, limited visibility into code, false positives

SAST vs. DAST by Vulnerability Class

Vulnerability	SAST Detection	DAST Detection
Injection (SQLi, command)	Excellent, analyzes data flows	Good, manipulation attacks
Broken authentication	Limited, some logic flaws	Excellent, auth bypass testing
XSS, injection	Excellent, patterns and analysis	Good, confirms exploitable flaws
Insecure design	Good, control flow flaws	Limited, some logic issues
Exposed resources	Limited,Some access controls	Excellent, probes for misconfigured ACLs
Cryptographic issues	Good, uses APIs incorrectly	Limited, confirms crypto operated
Config errors	None, requires runtime context	Excellent, assesses production config

Hybrid Analysis with Interactive Application Security Testing

Interactive application security testing (IAST) combines SAST and DAST capabilities for more comprehensive testing. IAST instruments application code and monitors execution to link runtime behavior back to code.

IAST provides benefits like:

Code-level visibility into vulnerabilities like DAST
Low overhead like SAST while testing running software
Eliminates many false positives by validating findings in code
APIs allow IAST integration into CI/CD workflows

However, IAST requires application changes for instrumentation. Organizations may prefer traditional SAST and DAST solutions.

Determining When to Use SAST vs DAST

Choosing whether to implement SAST or DAST depends on your application security objectives:

Use SAST For:

New development – embed into coding before bad habits form. Uncover flaws early.
Code reviews – augment human code reviews with automated scanning
Regulated environments – meet compliance requirements for static code analysis
CI/CD integration – embed into devops pipelines to automate security testing

Use DAST For:

Existing applications – assess operational software with no code changes
Acquired applications – test 3rd party purchased code and binaries
Production systems – evaluate actual attack surface and configuration
Defense in depth – complement SAST with runtime validation

Using SAST and DAST Together for Comprehensive Testing

While often positioned as competing alternatives, SAST and DAST are actually complementary when used as part of an overarching application security program.

Organizations should leverage both SAST and DAST across the software development lifecycle:

Use SAST during development to uncover coding flaws early when cheaper to fix
Confirm weaknesses with DAST against staged builds before release
Follow up with ongoing DAST scans of production apps to detect new threats

SAST finds flaws earlier in code. DAST confirms which manifest at runtime. This layered approach delivers comprehensive results.

For example, SAST can identify injection vulnerabilities like SQLi in code before applications are even built. DAST then validates those issues are exploitable in practice. This eliminates false positives.

An Integrated Approach with DevSecOps

To fully unify security into modern CI/CD pipelines, organizations are adopting DevSecOps models. DevSecOps tightly integrates security tools like SAST and DAST into automated workflows.

DevSecOps Pipeline

In a DevSecOps pipeline, SAST and DAST testing can be implemented continuously:

SAST scans executed on code commits and pull requests to provide rapid feedback on flaws
DAST scans performed against staging deployments to catch configuration and runtime issues
Security gates prevent release if critical vulnerabilities are detected
Issues tracked and remediation enforced using application lifecycle management
Results integrated into developer workflows through IDE plugins and fail-fast builds

This automated process shifts security left, enabling collaborative development and security teams to find and resolve bugs at speed.

Open Source vs. Commercial SAST and DAST Tools

There are a wide variety of both open source and commercial SAST and DAST tools available:

Open Source AppSec Tools

SAST

SpotBugs – static analysis for Java code. Fast and incrementally scan code.
Checkstyle – code style enforcement for Java. Plugins for IDE integration.
FindSecBugs – open source security auditing plugin for Java applications.

DAST

OWASP ZAP – top open source web app scanner with automated and manual modes.
OWASP Dependency-Check – detects publicly disclosed vulnerabilities in application dependencies.
W3af – extensible scanning framework with web app fuzzing, SQLi detection, and more.

Commercial AppSec Tools

SAST

Fortify – end-to-end SAST solution part of MicroFocus. Deep data flow analysis and IDE integration.
Checkmarx – adapter-based code scanning with extensive vulnerability coverage and compliance reporting.
Veracode – on-demand and CI/CD-integrated SAST scanning. Supports 25+ languages.

DAST

Burp Suite – advanced web vulnerability scanner with an integrated proxy for manual testing.
Rapid7 InsightAppSec – DAST combining passive and active scanning to reduce disruption and false positives.
Contrast Security – DAST solution combining external vulnerability testing and runtime application monitoring.

Commercial tools like Fortify and Burp Suite offer a level of sophistication unmatched by most free options. Organizations with rigorous security requirements may require advanced capabilities.

However, open source AppSec tools have improved considerably over the years. Feature gaps have narrowed making open source a viable option for teams operating on limited budgets.

Which Is Better for Application Security – SAST or DAST?

Based on their complementary strengths, both SAST and DAST testing should be leveraged as part of an end-to-end AppSec program.

Relying on any single testing method will leave coverage gaps. Organizations need layered security utilizing different techniques and perspectives.

For the strongest application security posture:

Perform SAST testing during development to uncover flaws early and promote secure coding habits
Validate findings with DAST against staged releases to confirm vulnerabilities
Follow-up with ongoing DAST scans against production apps
Pursue DevSecOps integration to automate SAST and DAST testing in CI/CD pipelines

SAST and DAST work hand-in-hand to find vulnerabilities, reduce risk, and secure critical application workloads throughout their lifecycle.

Key Takeaways from Our In-Depth SAST and DAST Comparison

SAST analyzes source code for bugs, while DAST tests running apps for functional and configuration issues.
SAST testing during development uncovers flaws earlier when cheaper to fix. DAST assess attack surface exposed at runtime.
Organizations should use SAST and DAST together across the entire app lifecycle for layered security.
Integrate SAST and DAST into CI/CD pipelines as part of DevSecOps programs to automate security.
Both commercial and open source SAST and DAST tools are available depending on needs and budget.
For optimal application security, utilize SAST plus DAST instead of choosing only one approach.

Now over to you – do you have experience using SAST, DAST, or both? Which application security testing approach has been most effective for your organization? Share your lessons learned!