Application Security

Application security covers the processes and tools that protect software against vulnerabilities and attacks. It involves building security into applications from design through to operations, and continuously testing for new risks.

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What is application security?

Application security (AppSec) is the collective practice of identifying, remediating and preventing security vulnerabilities in software. It applies to web applications, mobile apps, APIs and back-end systems.

Where network segmentation and firewalls protect infrastructure, application security focuses on the code and logic that drive your systems. An application may sit behind the most advanced endpoint security, but if the code contains SQL injection or broken access control, the organisation is vulnerable.

Application security spans several disciplines: secure coding, code review, automated testing, vulnerability scanning and penetration testing. Together they create a defence that covers the entire application lifecycle.

Methods and test types

Application security relies on several complementary test methods:

SAST (Static Application Security Testing): Analyses source code without running the application. Identifies vulnerabilities early in the development cycle, such as hard-coded credentials or buffer overflows.
DAST (Dynamic Application Security Testing): Tests the running application by sending malicious requests. Discovers runtime issues such as cross-site scripting (XSS) and injection attacks.
SCA (Software Composition Analysis): Scans third-party libraries and open-source components for known vulnerabilities. Essential, as most applications rely on hundreds of dependencies.
IAST (Interactive Application Security Testing): Combines SAST and DAST by instrumenting the application during testing. Delivers precise results with fewer false positives.

Beyond automated tests, manual penetration tests remain important. An experienced tester finds logic errors and business-logic vulnerabilities that automated tools miss.

Security in the development lifecycle

The most effective approach to application security is integrating it across the entire Software Development Life Cycle (SDLC). This approach is often called "shift left", because security moves from the late testing phases to the early design phases.

In practice this means:

Requirements phase: Define security requirements alongside functional requirements. Consider threat modelling to identify potential attack vectors.
Design: Apply principles such as least privilege and defence in depth. Choose secure architecture patterns and plan encryption of sensitive data.
Implementation: Use secure coding guidelines and automated SAST in the CI/CD pipeline. Conduct code reviews with a security focus.
Testing: Run DAST and vulnerability scanning against test environments. Carry out penetration tests before major releases.
Operations: Monitor with SIEM systems, manage patching of dependencies and have an incident response plan ready.

This approach requires developers to have fundamental security awareness. Regular training in secure development is a prerequisite for succeeding with AppSec.

Regulations and standards

Several regulations and standards impose direct or indirect requirements on application security:

ISO 27001 Annex A contains controls for secure system development (A.8.25–A.8.28), including requirements for secure coding rules, testing and protection of test data. An ISMS implementation should cover application security as part of technical and organisational measures.

DORA requires financial entities to test their ICT systems regularly, including applications. NIS2 imposes similar requirements on essential and important entities.

CIS 18 dedicates Control 16 to application security, with a focus on establishing and maintaining a secure development process.

Under GDPR, application security is relevant as a technical measure for protecting personal data. A vulnerable application that exposes personal data can lead to fines and loss of trust.

Frequently Asked Questions about Application Security

What is the difference between application security and network security?

Application security focuses on protecting the software itself against vulnerabilities in code and design, whereas network security protects the infrastructure the application runs on. Both are necessary for a strong defence.

When should application security be part of the development process?

Application security should be included from the very first design phase. The 'shift left' approach means security is considered during requirements and architecture, not only at the testing or operations stage.

Which standards require application security?

ISO 27001 Annex A contains controls for secure development. DORA imposes requirements on financial entities' ICT systems. CIS 18 has dedicated controls for application security. OWASP Top 10 is a widely recognised reference framework.

What is OWASP Top 10?

OWASP Top 10 is a list of the ten most critical security risks in web applications. The list is updated regularly and is used as a baseline for application security in many organisations and regulations.