What is application security (AppSec)?

• Application security now extends far beyond web applications to include APIs, cloud-native applications, AI systems, agents, containers, and embedded software.  
• Modern applications process and connect to critical data. A vulnerable application can expose your sensitive information, business processes, privileged systems, and cloud resources.
• Security testing approaches such as SAST, DAST, and application security posture management (ASPM) help you identify different types of application risk across the software lifecycle.
• Application security is a critical input to exposure management, helping you understand which static code vulnerabilities create meaningful business risk so you can prioritize them for remediation.

Applications process your most sensitive data. They connect your systems and power your critical business processes. When an application is compromised, attackers do not just reach that application. They reach everything it touches.

Application security is the practice of finding, assessing, and reducing software vulnerabilities throughout the application lifecycle.

Modern applications consist of interconnected components spanning cloud environments, APIs, mobile clients, open-source libraries, AI services, containers, and third-party integrations.

As a result, application security now covers:

• Web applications
• APIs
• Mobile apps
• Cloud-native apps
• Containers and Kubernetes environments
• Open-source software dependencies
• AI-powered apps
• AI agents and automation workflows
• Embedded software and connected devices

Applications run on data. If an application is compromised, attackers can access proprietary information, privileged systems, and critical business processes.

You see this challenge in everyday application security scenarios: 

• An insecure login system can expose user identities.
• An insecure API can expose customer data. 
• A compromised AI tool can access information it shouldn’t. 
• A vulnerable open-source library can provide a stepping stone into production systems.

Modern applications include web interfaces, APIs, mobile endpoints, third-party integrations, and AI components. Each layer expands the risk surface.

Securing applications is not something you can do during the development cycle. 

With AI generating code, better attack tools, and shorter development cycles, you need to continuously test and prioritize safety measures.

Application security helps limit those risks through continuous testing, monitoring, and prioritization.

The OWASP Top 10 and the OWASP API Security Top 10 are the two most widely adopted frameworks for web application and API vulnerability risk. While some application code vulnerabilities are published in the Common Vulnerabilities and Exposures (CVE) database, the vast majority of flaws are categorized based on OWASP frameworks.

Security teams use them to focus remediation efforts on the categories most likely to cause real damage, not just the ones that look alarming in a scan report.

These frameworks outline major vulnerability categories for modern applications, helping your security teams focus on issues that need fixing.

Broken access control, broken authentication, and injection flaws appear in both frameworks and in the majority of real-world breach investigations.

Attackers rely on them because they are structurally common and give broad access to data and systems when exploited.

Security misconfiguration follows the same pattern for a different reason: it requires no sophisticated exploit, just a preventable error that exposure management is designed to surface before an attacker does.

One of the most common questions in application security testing is SAST vs. DAST vs. runtime security testing. All approaches provide valuable insight, but they examine applications differently.

Static application security testing

Code that looks clean in development can become an exploitable path in production. Static application security testing (SAST) finds those issues before deployment, when fixing them costs a fraction of what a post-release patch cycle requires.

SAST can detect hardcoded credentials, insecure cryptographic implementations, unsafe function calls, injection vulnerabilities, coding errors, and security misconfigurations.

Because SAST examines code directly, it supports shift-left security practices by helping developers address issues before deployment.

However, SAST cannot fully evaluate how an application behaves in production.

Dynamic application security testing

Dynamic application security testing (DAST) evaluates a running application from the outside.

Rather than reviewing source code, DAST interacts with the application the way an attacker would. A DAST solution may test authentication workflows, probe API endpoints, submit malicious inputs, analyze application responses, and identify exploitable vulnerabilities.

DAST often reveals risks that static analysis cannot detect, including runtime configuration issues, authentication weaknesses, and live injection vulnerabilities.

Tenable One Web App Scanning provides automated DAST capabilities for web applications and APIs. It helps organizations identify vulnerabilities aligned with both the OWASP Top 10 and the OWASP API Security Top 10 while supporting modern DevSecOps security testing workflows.

What is application security posture management (ASPM)?

Most organizations already run multiple security tools.

SAST, DAST, runtime security, cloud security, and API testing solutions often operate independently.

Application security posture management (ASPM) helps unify application security findings from multiple tools into a single risk view.

ASPM connects those findings.

Application security posture management helps you answer questions such as:

• Which vulnerabilities are attackers able to access externally?
• Which applications process sensitive or confidential information?
• What risks affect production environments?
• Which vulnerabilities can fuel real business exposure?
• Which risks require immediate attention?

Instead of managing dozens of disconnected dashboards, you gain a clearer understanding of application risk across your portfolio.

Applications increasingly communicate through APIs. Microservices, mobile applications, cloud platforms, partner integrations, and AI systems all rely on APIs to exchange information.

API proliferation

As API usage expands, so does API-related risk.

The OWASP API Security Top 10 focuses on threats specific to application programming interfaces.

One of the most important categories is Broken Object Level Authorization (BOLA). This vulnerability occurs when an API exposes objects or records that authenticated users should not access.

APIs often provide direct access to data and business functionality. As a result, API vulnerabilities can expose customer information, business processes, and sensitive systems much faster than traditional web application vulnerabilities.

Modern API security testing helps identify threats and verify that authorization controls work as intended.

AI integration

AI comes with new attack surfaces, too. You are increasingly integrating large language models into applications, platforms, and workflow processes. 

For instance, prompt injection aims to alter an AI system’s behavior via carefully crafted input. 

An attacker may attempt to override safeguards, reveal sensitive information, perform unauthorized actions, or manipulate business processes. 

Traditional application security tools were not designed to identify these risks. 

As AI becomes part of production applications, prompt injection has become an application security concern rather than a standalone AI concern.

AI-assisted coding

While AI-assisted coding speeds up development, it also introduces new security issues. 

These tools might copy unsafe coding patterns, introduce vulnerable dependencies, and introduce new functionalities that developers don’t fully understand or have not reviewed.

As development velocity increases, application security testing becomes even more important. Security teams need visibility into both the code being created and the risks that code introduces.

AI agents

AI agents introduce a fresh kind of risk in apps. They can handle multi-step tasks, interact with external services, and make decisions on their own more than traditional apps can.

This independence shifts how risks are seen. If a web application is compromised, only that application is affected. 

However, if an AI agent is taken over, it can interact with many systems, APIs, data sources, and business processes. 

When attackers manipulate an agent, they can influence activity across several systems at once.

As you introduce agents into production workflows, security teams need visibility into:

• What actions agents can perform
• Which systems they can access
• What permissions they inherit
• Which external services they can interact with
• How they respond to unexpected inputs

As a result, AI-aware testing, runtime monitoring, and continuous visibility have become essential application security best practices.

Application security and cloud security increasingly overlap. 

Modern applications depend on containers, Kubernetes, serverless functions, Infrastructure as Code (IaC), microservices, and cloud APIs.

A vulnerability may originate in application code, but the resulting exposure often involves cloud infrastructure, identities, permissions, configurations, and data stores.

Infrastructure as Code (IaC) security

Infrastructure as Code allows teams to deploy environments at scale.

However, IaC templates can also introduce misconfigurations at scale.

Excessive permissions, exposed storage services, insecure network configurations, and publicly accessible resources can all originate in IaC definitions long before an application reaches production.

Containers and Kubernetes security

Containers and Kubernetes have transformed how applications are built and deployed.

While they improve agility, they also create new attack paths. 

Vulnerable container images, excessive permissions, insecure secrets management, exposed orchestration interfaces, and weak segmentation can all increase application risk.

Application security now extends beyond source code to include the environments where applications run.

Cloud exposure and CNAPP

Cloud-native application protection platforms (CNAPPs) give you visibility into risk across applications, cloud infrastructure, identities, and workloads.

This broader visibility is important because attackers seldom stop at a single vulnerability.

An application flaw may provide access to a cloud workload. A cloud misconfiguration may expose sensitive data. Excessive identity permissions may allow lateral movement into critical systems.

This convergence has accelerated the adoption of integrated approaches that combine application, cloud, identity, and infrastructure visibility.

Application security increasingly contributes to broader exposure management and exposure assessment programs because application vulnerabilities rarely exist in isolation.

Tenable supports application security as part of a wider exposure management and exposure assessment program.

Finding vulnerabilities is only the beginning; establishing whether it creates meaningful business risk is key. Exposure management helps answer that question.

Context for risk assessment

A critical vulnerability may not matter if attackers cannot reach it. 

A medium-severity vulnerability may deserve immediate attention if it sits on a path to sensitive data, privileged identities, or critical infrastructure.

Tenable One connects application findings to cloud assets, identities, infrastructure, and attack paths to provide more context for risk assessment.

Instead of analyzing application vulnerabilities in isolation, security teams gain a clearer understanding of how application weaknesses contribute to overall exposure.

Identifying vulnerabilities that matter

Attack path analysis helps identify vulnerabilities that realistically serve as entry points to valuable assets.

This allows you to prioritize remediation based on business impact rather than relying solely on vulnerability scores.

For example, your DAST tool may identify a moderately severe injection vulnerability in a customer-facing web application. 

Attack path analysis may show that attackers could exploit that vulnerability to access an internal API and then reach a sensitive customer database hosted in the cloud.

Tenable One identifies that attack path and elevates the finding’s priority based on its potential business impact, not solely on its CVSS score.

As a result, your team can focus remediation efforts on areas that reduce risk the most.

Accelerating remediation

Tenable Hexa AI helps security teams correlate findings, identify responsible owners, and accelerate remediation workflows across complex environments.

By connecting findings to the right teams and providing additional context, Tenable Hexa AI helps reduce the time between discovery and remediation.

Application security comes with a whole host of questions the many people commonly ask. Between the many acronyms and types of testing, let's get many of those frequently answered questions answered here.

What is application security?

Application security is the practice of identifying, assessing, and reducing vulnerabilities across applications before attackers can exploit them. It covers web applications, APIs, cloud-native applications, AI-powered systems, open-source dependencies, and supporting infrastructure.

What is the difference between SAST and DAST?

SAST analyzes code without running the application. DAST evaluates a live application from the outside by simulating attacker behavior. Most organizations use both because they identify different types of risk.

What is runtime application security?

Runtime security monitors application behavior during execution to identify vulnerabilities, unusual activity, unsafe code execution, and risks that may not appear during static or dynamic testing.

How does API security differ from web application security?

API security focuses on machine-to-machine communication, authorization controls, authentication mechanisms, and API-specific vulnerabilities such as Broken Object Level Authorization (BOLA).

What is prompt injection?

Prompt injection is an attack technique that attempts to manipulate the behavior of an AI system through carefully crafted input. Both external threat actors and malicious insiders may use prompt injection to bypass AI security controls, expose information, or influence system behavior.

What security risks do AI agents introduce?

AI agents can perform actions autonomously, access multiple systems, and operate at machine speed. If attackers manipulate an agent, the impact can extend across several applications, services, and business processes.

How does application security fit into exposure management?

Application security identifies vulnerabilities, while exposure management determines which vulnerabilities pose meaningful business risk by factoring in other elements like identities, cloud assets, infrastructure, and attack paths.

How does Tenable test web applications and APIs?

Tenable Web App Scanning uses Dynamic Application Security Testing (DAST) to assess web applications and APIs for vulnerabilities associated with the OWASP Top 10 and the OWASP API Security Top 10.

What is the difference between DAST and penetration testing?

DAST automates live application testing and supports repeatable assessments. Penetration testing depends on human expertise to identify complex attack paths, business logic flaws, and chained vulnerabilities. Organizations often use both approaches together.