API Security
Protecting application programming interfaces, whose risk profile differs from traditional web applications because there is no browser enforcing a same-origin policy, business logic is directly exposed, and object-level authorisation must be checked on every call. The OWASP API Security Top 10 names broken object-level authorisation, broken authentication and broken object property-level authorisation as the leading categories. Examined in GWAPT, eWPT, CSSLP and CCSP.
Why It Matters
In practice APIs fail on authorisation far more than on injection, and the reason is structural: a web page hides fields the user should not see, while an API returns objects and trusts the client to display only some of them -- so excessive data exposure and mass assignment are endemic, and the fix is explicit server-side allow-lists of readable and writable properties per role rather than serialising a whole model. The second recurring problem is inventory: undocumented, deprecated and shadow endpoints (v1 left running beside v2, staging exposed to the internet) are exploited constantly because nobody knew they were reachable, which makes an accurate API inventory a security control rather than documentation. Rate limiting matters more than for web apps too, since APIs are designed for automation, so per-consumer quotas are what prevent scraping and credential-stuffing at scale. Gateways help with authentication and throttling but cannot make object-level authorisation decisions. On exams, expect questions on BOLA and mass assignment.
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Test your knowledge of API Security concepts with exam-style practice questions.
Related Application Security terms
OWASP
The Open Web Application Security Project, a nonprofit foundation focused on improving software security through community-led open-source projects, tools, documentation, and standards. OWASP is best known for the OWASP Top 10, a regularly updated list of the most critical web application security risks (including injection, broken authentication, XSS, and security misconfiguration). Other key projects include the OWASP Testing Guide, ASVS (Application Security Verification Standard), ZAP (Zed Attack Proxy), and the Mobile Security Testing Guide. OWASP resources are referenced across virtually every security certification and are the de facto standard for web application security assessments.
SAST (Static Application Security Testing)
A testing methodology that analyzes source code, bytecode, or binary code for security vulnerabilities without executing the program, often called 'white-box' testing. SAST tools scan codebases for patterns that match known vulnerability types such as SQL injection, XSS, buffer overflows, and hardcoded credentials. They integrate into CI/CD pipelines to catch issues early in the development lifecycle (shift-left security). Popular SAST tools include SonarQube, Checkmarx, Semgrep, and Fortify. SAST complements DAST (runtime testing) and is a fundamental practice in DevSecOps and secure SDLC, tested in CSSLP and DevSecOps certifications.
DAST (Dynamic Application Security Testing)
A testing methodology that analyzes running applications for vulnerabilities by simulating external attacks without access to source code, often called 'black-box' testing. DAST tools interact with the application through its interfaces (HTTP requests, APIs) to find issues like injection flaws, authentication problems, configuration errors, and sensitive data exposure. Unlike SAST, DAST finds runtime-specific issues but cannot pinpoint the exact line of vulnerable code. Popular DAST tools include OWASP ZAP, Burp Suite, Nikto, and Acunetix. DAST is used alongside SAST in a comprehensive application security program and is tested in CEH, OSCP, and DevSecOps certifications.
DevSecOps
An approach that integrates security practices within the DevOps process throughout the entire software development lifecycle, making security a shared responsibility rather than an afterthought. DevSecOps automates security testing at every stage: SAST in code commits, dependency scanning in builds, DAST in staging, infrastructure-as-code scanning, and container image scanning before deployment. Key principles include shift-left security, security as code, automated compliance checks, and continuous monitoring in production. Tools include GitHub Advanced Security, Snyk, HashiCorp Vault, and Falco. DevSecOps is increasingly tested in CISSP, CSSLP, and dedicated DevSecOps foundation certifications.
CSRF (Cross-Site Request Forgery)
An attack that forces authenticated users to submit unwanted requests to a web application where they are currently logged in, exploiting the trust that the site has in the user's browser. For example, an attacker could craft a link that transfers funds or changes account settings when clicked by a logged-in user. CSRF works because browsers automatically include session cookies with every request to a domain. Defenses include anti-CSRF tokens (synchronizer tokens), SameSite cookie attributes, checking the Origin/Referer headers, and requiring re-authentication for sensitive actions. CSRF is an OWASP Top 10 vulnerability and is tested in CEH, OSCP, and web application security certifications.
Mobile Application Security
The practice of securing mobile apps and the data they hold, spanning insecure local storage, weak transport protection, hardcoded secrets in the package, misused platform APIs, and inadequate resistance to reverse engineering or tampering on a device the owner fully controls. The OWASP Mobile Application Security Verification Standard (MASVS) and its testing guide define the accepted requirement levels, and OWASP MASVS is a certification track in its own right. Mobile app security appears in CMPen-Android, eMAPT, OWASP MASVS and CSSLP domains.