Architectural Differences

DAST architecture centers on external testing engines that interact with applications through their exposed interfaces. Scanners send crafted requests designed to trigger vulnerabilities, then analyze responses for signs of successful exploitation. This architecture requires no modification to target applications, making DAST universally applicable regardless of technology stack or deployment model. The separation between scanner and application enables testing of third-party applications, legacy systems, or any application where code modification isn't possible.

IAST architecture embeds sensors within applications through agents, libraries, or runtime modifications. These sensors observe application behavior during execution, tracking data flow, monitoring security controls, and identifying vulnerability patterns. Agents might attach to application runtime environments (JVM, CLR, Node.js runtime) or integrate through application libraries. This tight integration provides complete visibility into application behavior but requires compatible runtime environments and deployment permissions.

The architectural distinction drives fundamental differences in capabilities. DAST's external position limits visibility to observable behaviors but ensures universal applicability. IAST's internal position provides complete visibility but requires specific integration for each technology stack. These trade-offs influence tool selection based on application portfolios and security requirements.