Identification of Improper Handling of JWTs (JSON Web Tokens)

Identifying improper handling of JSON Web Tokens (JWTs) involves examining how JWTs are generated, transmitted, and validated within a web application. Improper handling of JWTs can lead to security vulnerabilities such as unauthorized access, tampering, or information disclosure. Here's how you can identify such issues:


  1. Reviewing JWT Generation: Examine how JWTs are generated within the application. Check if strong cryptographic algorithms and key lengths are used to sign the tokens. Look for insecure random number generation or predictable token values.
  2. Analyzing JWT Storage: Check where JWTs are stored within the application. Look for vulnerabilities such as storing JWTs in client-side storage mechanisms (e.g., local storage, session storage) where they may be accessible to attackers via XSS attacks.
  3. Inspecting JWT Transmission: Review how JWTs are transmitted between the client and server. Look for vulnerabilities such as transmitting JWTs over insecure channels (e.g., HTTP instead of HTTPS) or including them in URLs where they may be exposed to interception.
  4. Testing JWT Validation: Test how JWTs are validated by the application upon receiving them from clients. Look for vulnerabilities such as weak signature validation, lack of token expiration checks, or bypassable token validation logic.
  5. Analyzing Token Revocation: Check if the application supports token revocation mechanisms to invalidate JWTs in case of compromise or logout. Look for vulnerabilities such as lack of token revocation or improper implementation of token invalidation.
  6. Reviewing JWT Payload: Examine the contents of JWT payloads for sensitive information. Look for vulnerabilities such as including personally identifiable information (PII), sensitive user data, or access tokens in JWT payloads.


  • Example 1: During testing, a penetration tester discovers that the application uses weak cryptographic algorithms (e.g., HMAC with MD5) to sign JWTs. Attackers can exploit this weakness to forge or tamper with JWTs.
  • Example 2: The tester finds that the application stores JWTs in client-side storage (e.g., local storage) without proper encryption or protection. This exposes JWTs to theft via XSS attacks.


  1. Use Strong Cryptography: Use strong cryptographic algorithms (e.g., HMAC with SHA-256, RSA) and key lengths to sign and verify JWTs. Avoid using deprecated or insecure algorithms.
  2. Secure Token Storage: Store JWTs securely on the server-side and avoid storing them in client-side storage mechanisms vulnerable to XSS attacks. Use HTTP-only cookies for session management instead of client-side storage.
  3. Transmit JWTs Securely: Transmit JWTs over secure channels (e.g., HTTPS) to prevent interception or tampering. Avoid including JWTs in URLs or query parameters where they may be exposed to attackers.
  4. Implement Secure Validation: Implement secure JWT validation logic on the server-side, including checks for signature integrity, token expiration, and issuer verification. Use well-established JWT libraries or frameworks to handle token validation.
  5. Implement Token Revocation: Implement token revocation mechanisms such as token blacklisting or token expiration to invalidate JWTs after a certain period or upon user logout. Ensure that revoked tokens cannot be reused.
  6. Avoid Sensitive Data in Payload: Avoid including sensitive information such as passwords, access tokens, or PII in JWT payloads. Keep JWT payloads lightweight and limited to non-sensitive data whenever possible.

By identifying and mitigating improper handling of JWTs, organizations can enhance the security of their web applications and protect against unauthorized access or data exposure vulnerabilities.