Vendor application security testing

Third-party vendors now play a central role in delivering enterprise services, yet they also introduce some of the most difficult and opaque security risks. Many vendor applications connect directly to sensitive data, internal APIs, and user workflows. This creates a dependency chain that attackers increasingly exploit. Vendor application security testing helps CISOs, security architects, and compliance leaders understand exactly how vendor software behaves and where hidden risks exist. It also ensures assessments are standardized, repeatable, and aligned with modern frameworks.

What is vendor application security testing (VAST)?

Vendor application security testing is the process of evaluating third-party applications to identify vulnerabilities, insecure behaviors, and design flaws that could impact an organization’s security posture. VAST uses a structured set of testing methods to validate the security of vendor software before and after onboarding.

Why vendor application security testing is essential

• Vendor applications often run outside the organization’s direct development control even though they access sensitive systems.

• Many supply chain attacks begin with an untested vendor integration that exposes API keys, customer data, or authentication flows.

• Compliance frameworks such as SOC 2 and ISO 27001 require demonstrable vendor application security testing as part of third-party risk management.

• Continuous vendor monitoring is essential because vendor applications change frequently and silent updates can introduce new vulnerabilities.

• Vendor application security testing provides evidence for procurement, legal, and security reviews, reducing subjective decision making and improving risk accountability.

Key vendor application security testing methods

Below are the key testing methods used in a vendor application security testing program. Each method reveals different categories of vendor risk and requires different processes and tools.

DAST: Dynamic application security testing

Dynamic application security testing focuses on identifying vulnerabilities in a running application. Unlike code-level assessments, DAST simulates real attacker behavior against the live interface. This makes it well suited for evaluating vendors whose code you do not have access to. In vendor scenarios, you often evaluate SaaS products or externally hosted applications where you can only see the exposed surface, not the implementation. DAST helps you understand how securely the vendor’s application handles requests, states, sessions, and workflows under real conditions.

Purpose

• Detect runtime issues such as authentication weaknesses, business logic bypasses, broken access controls, and insecure session handling.

• Validate how the vendor application behaves under real-world scenarios rather than theoretical code flaws.

Platforms

• Beagle Security

• OWASP ZAP

DAST plays a critical role in vendor assessments because it provides an outside-in perspective that mimics how attackers would interact with the vendor’s deployed application.

Tools like Beagle Security allow automated scheduling of recurring runtime tests, which is useful for continuous vendor monitoring. This is important because vendors frequently push silent updates without notifying customers, and continuous DAST helps detect new vulnerabilities introduced between periodic reviews.

SAST: Static application security testing

Static application security testing is used when a vendor provides access to source code or when you evaluate internal applications built by vendors under contract. While not always possible with commercial vendors, SAST is common in outsourced development relationships where the customer has contractual authority to audit the code. SAST helps identify vulnerabilities that runtime testing may not catch, especially insecure coding patterns that increase long-term maintenance or security risks.

Purpose

• Identify insecure coding patterns, hardcoded secrets, and data flow problems.

• Catch vulnerabilities early if vendors are required to submit code as part of contract deliverables.

Platforms

• Semgrep

• SonarQube

SAST is most relevant when organizations have strong contractual control over vendors or perform detailed software composition reviews. For traditional SaaS vendor evaluations, SAST is usually optional.

API security testing

API security testing is increasingly critical because many vendor products integrate directly into enterprise systems using APIs. APIs form the glue between internal and external systems, which means that insecure vendor APIs can expose sensitive data or allow unintended operations. Vendors often evolve their APIs rapidly, which creates opportunities for design mistakes or poor access control.

Purpose

• Validate authentication, API token handling, rate limiting, and data exposure.

• Identify sensitive endpoints that vendors may not document.

• Detect business logic flaws in API workflows.

Platforms

• Beagle Security

• Salt Security

API security testing should be included in every vendor application security testing program because most modern vendors operate API-first or rely heavily on API calls for internal functions. Check out our list of Top API security vendors in 2025 if you want to know more

IAST: Interactive application security testing

Interactive application security testing combines elements of SAST and DAST by analyzing application behavior from inside the runtime environment. Because IAST instruments the application, it can see internal code execution paths, data flows, and library interactions as the application responds to test traffic. This unique perspective allows security teams to detect issues that neither SAST nor DAST can fully identify alone.

Purpose

• Detect vulnerabilities as the application executes.

• Provide deeper context for vulnerabilities discovered through DAST.

• Identify insecure libraries or flawed runtime logic.

Platforms

• Contrast Security

• Acunetix (with interactive capabilities)

IAST is ideal when the vendor deploys solutions inside the customer environment and supports instrumentation. It offers visibility into internal execution paths that external testing cannot capture.

SCA: Software composition analysis

Software composition analysis is essential for understanding the open source components embedded in vendor applications. Modern applications rely heavily on third-party libraries, packages, and frameworks. If these dependencies are outdated or unpatched, they can introduce high-risk vulnerabilities even if the vendor’s custom code is secure.

Purpose

• Identify vulnerabilities in open source libraries or third-party modules.

• Assess licensing risks and compliance issues.

• Provide insight into which components require patching or upgrading.

Platforms

• Snyk

• Mend.io

SCA is a mandatory component of many vendor assessments because even vendors with strong internal processes sometimes overlook dependency-level risks.

ASPM: Application security posture management

Application security posture management provides a continuous oversight layer across all testing activities. ASPM tools integrate findings from DAST, SAST, SCA, API tests, and penetration tests into a centralized system. This helps security teams get a single view of vendor risk instead of juggling disconnected reports and spreadsheets.

Purpose

• Offer unified dashboards for vulnerability trends across multiple vendors.

• Centralize evidence for compliance reviews.

• Identify vendors that need higher frequency testing or remediation follow-up.

Platforms

• Legit Security

• Cycode

ASPM strengthens a vendor application security testing program by ensuring that testing results are not siloed. It also supports automated workflows that reduce manual tracking across hundreds of vendors.

Best practices for vendor application security testing

Below are 6 best practices that strengthen vendor application security testing programs. Two of these specifically connect to Beagle Security capabilities as requested.

Establish tiered vendor risk levels

Classifying vendors based on the sensitivity of the data they access and their integration depth helps allocate assessment resources. High-risk vendors require deeper testing that includes DAST, API testing, and SCA, while low-risk vendors may only need security questionnaires and limited automated scans. Tiering ensures compliance teams can manage large vendor ecosystems without bottlenecks.

Require evidence based on testing type

Vendor security reviews often rely heavily on self-attested questionnaires. To avoid blind trust, require evidence from specific testing types such as penetration test reports, SCA results, or API test summaries. This ensures the vendor application security testing process aligns with compliance obligations under SOC 2 and ISO 27001. It also protects against vendors who overstate the maturity of their security programs.

Implement continuous testing for high-risk vendors

Vendor applications change frequently, and updates can introduce vulnerabilities silently. Continuous DAST and API testing help security teams detect new risks without waiting for annual or onboarding assessments.

Beagle Security supports automated recurring tests, scheduling, and change detection which makes it easier to enforce continuous vendor monitoring.

Validate business logic vulnerabilities during integration

Business logic flaws rarely appear in vulnerability scanners yet they are among the most abused weaknesses in real-world breaches. Vendor applications with complex workflows require targeted runtime tests that replicate actual user journeys.

Beagle Security’s logic-based scenarios allow security teams to test vendor workflows that cross multiple endpoints or involve privilege escalation paths. This strengthens the vendor application security testing program by covering risks that standard scanning tools cannot detect.

Align assessments with contractual commitments

Vendor contracts should include clear requirements for vulnerability remediation timelines, frequency of reassessment, disclosure of material security incidents, and use of secure development practices. Aligning tests with contract terms ensures that vendor security expectations are enforceable rather than aspirational. This protects the organization when vendors delay fixes or fail to notify customers about incidents.

Track remediation and response maturity

Testing vendors is only one part of the process. How vendors respond to findings reveals their operational maturity. Vendors that delay fixes, provide vague timelines, or treat vulnerabilities as low priority present long-term risks. Tracking vendor responsiveness over time helps organizations identify which vendors can be trusted and which require stronger controls or potential offboarding.

Final thoughts

Vendor application security testing is now essential as supply chain risks grow more complex. A structured VAST program helps leaders identify vulnerabilities, verify vendor claims, and uncover hidden risks in running applications and APIs. With continuous monitoring and clear remediation expectations, organizations can prevent third-party relationships from becoming weak points in their security posture.

For teams strengthening their programs, Beagle Security offers automated DAST and API testing that supports continuous vendor evaluation. You can explore its capabilities through a free 14-day advanced trial or walk through the interactive demo to see how it fits into a mature vendor assessment workflow.

Written by

Gincy Mol A G

AI Engineer

Contributor

Nandagopal S

Marketing Associate