Is JWT Really Secure? Pros, Cons, and Common Pitfalls Explained

If you often follow online project tutorials, you’ll notice many of them use JWT. But how safe is it really, and why do many experts advise against it? This article explores JWT from multiple angles, covering its definition, workflow, drawbacks, and security considerations.

What Is JWT?

JWT stands for JSON Web Token. It’s essentially a piece of JSON data that can be verified to originate from a trusted source. Think of it as a signed package containing claims about a user’s identity.

Below is the typical JWT workflow:

When you log into a website, the server generates a JWT and sends it to you.

The JWT acts like a parcel containing information such as username, roles, and permissions.

You include this JWT in every subsequent request to the site.

When accessing a protected page, the server expects the JWT to be presented.

The server verifies the JWT’s signature and checks the claims to confirm identity and permissions.

If verification succeeds, you gain access to the protected resource.

Why Is JWT Considered Problematic?

Typical web applications perform the following actions:

User registration

User login

User-initiated actions

Server creates, updates, or deletes data based on user information

These operations often involve database interactions such as recording user actions, adding data, and checking permissions.

Size Overhead

Storing a simple user ID in a cookie may take only a few bytes, but encoding the same ID in a JWT can increase the payload size by roughly 50 times, adding unnecessary bandwidth load.

Redundant Signatures

One of JWT’s selling points is its cryptographic signature, which allows the receiver to verify authenticity. However, most modern web frameworks already provide signed (and often encrypted) session cookies, offering the same benefits without needing JWT.

In many cases, JWT data is stored in a session cookie, resulting in two layers of signatures: one on the cookie itself and another on the JWT.

Token Revocation Issues

Because a JWT remains valid until it expires, servers lack a straightforward way to revoke it. This can lead to several risky scenarios:

Logout Does Not Invalidate Token

Even after a user logs out, the JWT may still be usable until its expiration time, allowing continued access if the token is intercepted.

Stale Permissions

If a user’s role is downgraded, the existing JWT may still grant elevated privileges until it expires.

Lack of Encryption

JWTs are typically not encrypted, so a man‑in‑the‑middle attacker who can read the token can obtain authentication credentials.

Security Concerns

For an in‑depth security analysis, see the following resources:

https://research.securitum.com/jwt-json-web-token-security/

https://www.freebuf.com/articles/web/375465.html

Conclusion

Overall, JWT is suitable as a single‑use authorization token for transmitting claims between two parties. However, it is not ideal for long‑term persistent storage , especially for managing user sessions. Using JWT for session management can introduce serious security and implementation issues; traditional session cookies remain a more mature and safer choice for persistent authentication.

That said, for learning or non‑production projects where security and performance are not critical, JWT can be perfectly acceptable.