Understanding Security Scanners
How DAST and SAST Work Under the Hood
Security scanners are automated tools that detect vulnerabilities in applications. They come in two main categories: Dynamic Application Security Testing (DAST) and Static Application Security Testing (SAST).
Both approaches are essential for comprehensive security coverage, but they work in fundamentally different ways and catch different types of vulnerabilities.
π―Why Security Scanners Matter
β‘ Speed and Scale
Automated scanners can test thousands of attack vectors in minutes, something impossible with manual testing alone.
π Continuous Security
Integrate into CI/CD pipelines to catch vulnerabilities before they reach production.
π Comprehensive Coverage
DAST finds runtime vulnerabilities, SAST catches code-level issues - together they provide complete coverage.
π° Cost Effective
Finding vulnerabilities early in development is 100x cheaper than fixing them in production.
πDAST: Dynamic Application Security Testing
DAST tools test running applications from the outside, simulating how an attacker would probe your web application. They don't need access to source code - they work like a hacker, sending malicious payloads and analyzing responses.
How DAST Works: Technical Workflow
1. Crawling / Spidering
The scanner discovers all endpoints, pages, and functionality in your application.
- Starts from a seed URL (usually the homepage)
- Follows all links, forms, and JavaScript-generated content
- Builds a complete sitemap of URLs, parameters, and entry points
- Discovers hidden directories and files (robots.txt, sitemap.xml)
- Identifies API endpoints and AJAX calls
- Maps out the application's attack surface
2. Authentication & Session Management
Handles login and maintains authenticated sessions to test protected areas.
- Records authentication flows (login, OAuth, SSO)
- Maintains session cookies and tokens
- Handles multi-step authentication (2FA, CAPTCHA bypass in test environments)
- Tests session timeout and logout functionality
- Checks for session fixation and hijacking vulnerabilities
- Verifies proper session invalidation
3. Active Vulnerability Scanning
Sends malicious payloads to every input point discovered during crawling.
- SQL Injection: Tests database query manipulation with special characters, UNION attacks, boolean/time-based blind injection
- Cross-Site Scripting (XSS): Injects JavaScript payloads to test reflection, storage, and DOM manipulation
- Command Injection: Tests OS command execution through input fields
- Path Traversal: Attempts to access files outside web root using ../ sequences
- XXE: Tests XML parsers for external entity injection
- SSRF: Attempts to make the server request internal/external resources
- Authentication Bypass: Tests for broken authentication and authorization
- CSRF: Checks for missing anti-CSRF tokens
4. Response Analysis
Analyzes server responses to determine if vulnerabilities exist.
- Checks HTTP status codes and error messages
- Looks for database error messages indicating SQL injection
- Detects reflected payloads in HTML responses (XSS)
- Measures response times for blind injection attacks
- Analyzes HTTP headers for security misconfigurations
- Validates SSL/TLS certificates and cipher suites
- Checks for sensitive data exposure in responses
5. Reporting & Verification
Generates detailed reports and reduces false positives.
- Categorizes findings by severity (Critical, High, Medium, Low)
- Provides proof-of-concept payloads for each vulnerability
- Includes exact request/response pairs
- Maps findings to OWASP Top 10 and CWE classifications
- Offers remediation guidance and code examples
- Attempts to verify and reduce false positives
Key Advantage: DAST finds vulnerabilities in the running application, including configuration issues, server-side problems, and complex multi-step attacks that only appear at runtime.
πSAST: Static Application Security Testing
SAST tools analyze source code, bytecode, or binary without executing the application. They work like a code reviewer, looking for insecure patterns, dangerous functions, and vulnerable code paths.
How SAST Works: Technical Workflow
1. Source Code Parsing
Reads and parses source code into analyzable structures.
- Supports multiple languages (Java, C#, Python, JavaScript, PHP, Ruby, Go, etc.)
- Parses code into tokens and syntax trees
- Handles compiled code (bytecode, binaries) when source isn't available
- Resolves imports, includes, and dependencies
- Builds a complete model of the application structure
2. Abstract Syntax Tree (AST) Generation
Converts code into a tree structure representing its logical structure.
- Represents code as a hierarchical tree of nodes
- Each node represents a construct (function, loop, condition, variable)
- Enables deep semantic analysis beyond simple pattern matching
- Allows tracking of data flow across complex code paths
- Preserves relationships between functions, classes, and modules
3. Data Flow Analysis
Tracks how data moves through the application from sources to sinks.
- Sources: User input (HTTP parameters, cookies, files, databases)
- Sinks: Dangerous functions (SQL queries, system commands, eval())
- Traces data from entry point to dangerous operation
- Identifies if user input reaches a sink without sanitization
- Handles complex flows through multiple functions and files
- Detects second-order vulnerabilities (stored XSS, delayed SQL injection)
4. Control Flow Analysis
Analyzes the order in which code executes and possible execution paths.
- Maps all possible execution paths through the code
- Identifies dead code and unreachable paths
- Detects authentication bypasses and logic flaws
- Checks for missing security checks before operations
- Analyzes conditional branches and loops
- Finds race conditions and concurrency issues
5. Taint Analysis
Tracks "tainted" (untrusted) data to ensure it's sanitized before use.
- Marks all user input as "tainted"
- Tracks tainted data through variables, functions, and objects
- Identifies sanitization functions that remove taint
- Flags when tainted data reaches a dangerous operation
- Detects insufficient or incorrect sanitization
- Handles complex propagation through encodings and transformations
6. Security Pattern Matching
Identifies known insecure coding patterns and anti-patterns.
- Hardcoded credentials and API keys
- Use of weak cryptographic algorithms (MD5, SHA1, DES)
- Insecure random number generation
- Dangerous functions (eval, exec, system, unserialize)
- Missing input validation or output encoding
- Insecure deserialization
- Missing security headers and configurations
7. Reporting & Prioritization
Generates actionable reports with precise code locations.
- Shows exact file, line number, and code snippet
- Provides data flow path from source to sink
- Categorizes by vulnerability type and severity
- Includes remediation code examples
- Maps to OWASP Top 10, CWE, and compliance standards
- Integrates with IDEs for real-time feedback
Key Advantage: SAST catches vulnerabilities early in development before code is deployed. It finds issues in code paths that might be difficult to reach with DAST, and provides exact locations for fixes.
βοΈDAST vs SAST: Key Differences
| Aspect | DAST | SAST |
|---|---|---|
| Testing Approach | Black-box (outside-in) | White-box (inside-out) |
| Requires Running App | β Yes | β No |
| Needs Source Code | β No | β Yes |
| When to Run | QA, Staging, Production | Development, Pre-commit, CI/CD |
| Speed | Slower (hours) | Faster (minutes) |
| False Positive | Lower | Higher |
| Finds Runtime Issues | β Yes (config, server) | β No |
| Shows Exact Code Line | β No | β Yes |
| Best For | XSS, SQLi, auth bypass, config | Hardcoded secrets, insecure crypto, injection flaws |
β Best Practices: Using Both Together
Start with SAST Early
Run SAST in the IDE and on every commit. Catch issues before they're committed.
Use DAST in QA/Staging
Run DAST against deployed environments to catch runtime and configuration issues.
Automate in CI/CD
Integrate both scanners into your pipeline. SAST on build, DAST after deployment.
Don't Rely on One
SAST and DAST catch different vulnerabilities. Use both for comprehensive coverage.
Verify and Prioritize
Manually verify critical findings. Focus on exploitable vulnerabilities first.
Tune Your Scanners
Configure authentication, reduce false positives, and customize rules for your stack.