What is JWT Security?

Understanding JWT Security

JSON Web Token (JWT) Security has become increasingly critical as these compact, self-contained tokens have become the standard for representing claims securely between applications, particularly in modern API architectures. Despite their widespread adoption, JWTs present several security challenges when improperly implemented. Common vulnerabilities include weak signature validation that allows attackers to modify token contents by changing the algorithm to “none” or switching from asymmetric to symmetric cryptography; insufficient verification of critical claims like expiration time or audience; and insecure storage exposing tokens to cross-site scripting attacks. Organizations implementing JWTs should adopt specific security practices: enforcing strong signature validation that rejects algorithm changes, implementing proper expiration with short-lived tokens, validating all relevant claims (issuer, audience, subject), using secure storage mechanisms, and ensuring tokens contain minimal sensitive information. The stateless nature of JWTs creates particular challenges around revocation—once issued, tokens remain valid until expiration unless implementers create server-side tracking mechanisms like blocklists. Security testing should specifically verify JWT implementations, as their popularity makes them attractive targets for attackers.