OWASP API Security Project

OWASP API Security Top 10 2023 RC is now available! Check out how to contribute.

What is API Security?

A foundational element of innovation in today’s app-driven world is the API. From banks, retail and transportation to IoT, autonomous vehicles and smart cities, APIs are a critical part of modern mobile, SaaS and web applications and can be found in customer-facing, partner-facing and internal applications. By nature, APIs expose application logic and sensitive data such as Personally Identifiable Information (PII) and because of this have increasingly become a target for attackers. Without secure APIs, rapid innovation would be impossible.

API Security focuses on strategies and solutions to understand and mitigate the unique vulnerabilities and security risks of Application Programming Interfaces (APIs).

API Security Top 10 2019

Here is a sneak peek of the 2019 version:

  • API1:2019 Broken Object Level Authorization

    APIs tend to expose endpoints that handle object identifiers, creating a wide attack surface Level Access Control issue. Object level authorization checks should be considered in every function that accesses a data source using an input from the user. Read more.

  • API2:2019 Broken User Authentication

    Authentication mechanisms are often implemented incorrectly, allowing attackers to compromise authentication tokens or to exploit implementation flaws to assume other user’s identities temporarily or permanently. Compromising a system’s ability to identify the client/user, compromises API security overall. Read more.

  • API3:2019 Excessive Data Exposure

    Looking forward to generic implementations, developers tend to expose all object properties without considering their individual sensitivity, relying on clients to perform the data filtering before displaying it to the user. Read more.

  • API4:2019 Lack of Resources & Rate Limiting

    Quite often, APIs do not impose any restrictions on the size or number of resources that can be requested by the client/user. Not only can this impact the API server performance, leading to Denial of Service (DoS), but also leaves the door open to authentication flaws such as brute force. Read more.

  • API5:2019 Broken Function Level Authorization

    Complex access control policies with different hierarchies, groups, and roles, and an unclear separation between administrative and regular functions, tend to lead to authorization flaws. By exploiting these issues, attackers gain access to other users’ resources and/or administrative functions. Read more.

  • API6:2019 Mass Assignment

    Binding client provided data (e.g., JSON) to data models, without proper properties filtering based on an allowlist, usually leads to Mass Assignment. Either guessing objects properties, exploring other API endpoints, reading the documentation, or providing additional object properties in request payloads, allows attackers to modify object properties they are not supposed to. Read more.

  • API7:2019 Security Misconfiguration

    Security misconfiguration is commonly a result of unsecure default configurations, incomplete or ad-hoc configurations, open cloud storage, misconfigured HTTP headers, unnecessary HTTP methods, permissive Cross-Origin resource sharing (CORS), and verbose error messages containing sensitive information. Read more.

  • API8:2019 Injection

    Injection flaws, such as SQL, NoSQL, Command Injection, etc., occur when untrusted data is sent to an interpreter as part of a command or query. The attacker’s malicious data can trick the interpreter into executing unintended commands or accessing data without proper authorization. Read more.

  • API9:2019 Improper Assets Management

    APIs tend to expose more endpoints than traditional web applications, making proper and updated documentation highly important. Proper hosts and deployed API versions inventory also play an important role to mitigate issues such as deprecated API versions and exposed debug endpoints. Read more.

  • API10:2019 Insufficient Logging & Monitoring

    Insufficient logging and monitoring, coupled with missing or ineffective integration with incident response, allows attackers to further attack systems, maintain persistence, pivot to more systems to tamper with, extract, or destroy data. Most breach studies demonstrate the time to detect a breach is over 200 days, typically detected by external parties rather than internal processes or monitoring. Read more.


The OWASP API Security Project documents are free to use!

The OWASP API Security Project is licensed under the Creative Commons Attribution-ShareAlike 3.0 license, so you can copy, distribute and transmit the work, and you can adapt it, and use it commercially, but all provided that you attribute the work and if you alter, transform, or build upon this work, you may distribute the resulting work only under the same or similar license to this one.



2023 Sponsors

Cequence Security


Impart Security

Salt Security


2023 Contributors

Alex Marks-Bluth, Alissa Knight, Arik Atar, Corey Ball, Dan Gordon, Dor Tumarkin, Isabelle Mauny, Ivan Novikov, Juan Pablo, Roey Eliyahu, Roshan Piyush, Yaniv Balmas, Zavodchik Maxim

2019 Contributors

007divyachawla, Abid Khan, Adam Fisher, anotherik, bkimminich, caseysoftware, Chris Westphal, dsopas, DSotnikov, emilva, ErezYalon, flascelles, Guillaume Benats, IgorSasovets, Inonshk, JonnySchnittger, jmanico, jmdx, Keith Casey, kozmic, LauraRosePorter, Matthieu Estrade, nathanawmk, PauloASilva, pentagramz, philippederyck, pleothaud, r00ter, Raj kumar, Sagar Popat, Stephen Gates, thomaskonrad, xycloops123, Raphael Hagi, Eduardo Bellis, Bruno Barbosa

Google Group

Join the discussion on the OWASP API Security Project Google group.

This is the best place to introduce yourself, ask questions, suggest and discuss any topic that is relevant to the project.


The project is maintained in the OWASP API Security Project repo.

The latest changes are under the develop branch.

Feel free to open or solve an issue.

Ready to contribute directly into the repo? Great! Just make sure you read the How to Contribute guide.

Planned Projects

  • API Security Top 10
  • API Security Cheat Sheet
  • crAPI - Completely Ridiculous API, an intentionally vulnerable API project)



OWASP API Security Top 10 2019