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OWASP top 10 API Security vulnerabilities – Broken Authentication
April 12, 2023
OWASP API Security Broken Authentication


Broken Authentication refers to the risk of weak or inadequate authentication controls in APIs, which can allow attackers to gain unauthorized access to the API. This can occur when the API uses weak or easily guessable passwords, fails to properly secure authentication tokens, or does not properly validate the authenticity of authentication credentials.


Some common risks associated with Broken Authentication include:

  • Unauthorized access to sensitive data or functionality
  • Compromise of user accounts
  • Elevation of privileges by unauthorized parties
Attack Scenarios

Attack scenarios for cloud applications may include:

  • An attacker intercepts an API call and captures an authentication token, then uses the token to access the API as the authenticated user
  • An attacker guesses or cracks a weak password to gain access to an API
  • An attacker exploits a vulnerability in the API’s authentication process to bypass authentication checks
Vulnerable Sample Code

A vulnerable sample of code in Go lang might look like this:

func login(w http.ResponseWriter, r *http.Request) {
  // Get the username and password from the request
  username := r.FormValue("username")
  password := r.FormValue("password")

  // Check if the username and password are correct
  if database.CheckCredentials(username, password) {
    // Generate an authentication token
    token, err := generateToken(username)
    if err != nil {
      http.Error(w, "Error generating token", http.StatusInternalServerError)

    // Return the token to the user
  } else {
    http.Error(w, "Invalid username or password", http.StatusUnauthorized)

In this example, the API call processes a login request by checking the provided username and password against a database. However, there are several vulnerabilities in this implementation: the password is transmitted in plaintext, there is no rate limiting to prevent brute force attacks, and there is no protection against session hijacking (e.g., by using secure cookies or rotating tokens). An attacker could exploit these vulnerabilities to gain unauthorized access to the API.

Sample Attack

A sample attack payload using the curl command might look like this:

curl -d "username=attacker&password=attacker_password" http://api.example.com/login

In this example, the attacker is using curl to send a login request with a malicious username and password. If the API is vulnerable to Broken Authentication, the attacker may be able to gain access to the API and potentially compromise user accounts.

MITRE ATT&CK framework reference

Broken Authentication can be mapped to the Tactic: Initial Access and the Techniques: Brute Force, Credential Dumping in the MITRE ATT&CK framework. These techniques involve exploiting vulnerabilities in authentication controls to gain unauthorized access to a system or network.


To mitigate the risk of Broken Authentication, organizations should ensure that they use strong and unique passwords for their APIs, and implement proper authentication and session management controls such as secure cookies or rotating tokens. Additionally, organizations should implement rate limiting to prevent brute force attacks, and properly validate and secure authentication credentials to prevent attacks such as credential stuffing. Regularly reviewing and testing the security of their API authentication processes can also help to identify and address vulnerabilities.

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