What is a JWT Token? -

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Introduction of JSON Web Token:

JSON Web Tokens, or JWTs, are a small, secure way for two parties to represent their claims. It is frequently used for permission and authentication in web development. Without continuously searching the database, a JWT enables servers to verify a user’s identity and make sure they have the necessary permissions.

A JWT typically has three parts:

Header—includes the token type and signature algorithm.
Payload—comprises the claims (permissions, expiration, and user information).
Signature—confirms that there hasn’t been any manipulation of the message.

Example:

CopyEdit
eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9.eyJ1c2VySWQiOiIxMjM0NSIsInJvbGUiOiJhZG1pbiJ9.qwertyuiop1234567890

[.] identifies the sections that are the header, payload, and signature.

Ex.

Headers == {eyJhbGciOiJIUzI1NiIsInR5cCI6IkpXVCJ9}
Paylaod == {eyJ1c2VySWQiOiIxMjM0NSIsInJvbGUiOiJhZG1pbiJ9}
Signature = ={qwertyuiop1234567890}

How JWT Works?

A user logs into an application.
The server creates a JWT after confirming the credentials.
The client receives the JWT, which is often saved in cookies or local storage.
This token is sent by the client with every request.
After confirming the token, the server either allows or prohibits access.

Impact and Importance of JWT

Benefits:

Some of the prime benefits of JWT are as follows:

Stateless Authentication	Because JWTs are self-contained, session state does not need to be maintained by the server.
Scalability	Beneficial in distributed systems and microservices where a central session store is ineffective.
Cross-Domain	JWTs can be used in APIs across many domains because they are stateless and URL-safe.
Performance	Enhances response speed and lowers server-side storage requirements.

Common JWT Vulnerabilities and Risks

Token Tampering

Certain systems might accept an unsigned token if the signature algorithm is changed from HS256 to none, which would enable attackers to create legitimate tokens.

Token Leakage

XSS attacks can be used to obtain JWTs that are stored insecurely, such as in localStorage.

No Expiration

The attack surface is increased by tokens with no expiration date (exp claim), which may be valid indefinitely.

Weak Signing Keys

Brute-force attacks are made simpler by using short or predictable secret keys.

Replay Attacks

Attackers can reuse tokens they have captured if they are not invalidated after usage or logout.

Mitigation Strategies

Use Strong Signing Algorithms

Use a secure algorithm, such as RS256 or HS256, at all times.
With alg: none, never accept tokens.

Secure Storage

To lessen XSS risk, use secure cookies that are only available over HTTP rather than localStorage.
If sensitive information is kept in JWTs, encrypt it (although it’s preferable to keep only IDs or references).

Set Expiry and Refresh Mechanism

Don’t forget to include the exp claim.
To safely prolong sessions, combine short-lived tokens with refresh tokens.

Validate All Claims

Verify the issuer, audience, and experience claims at all times.
User-modifiable fields should never be trusted without confirmation.

Implement Logout and Revocation

Make use of rotation techniques or token blacklists.
Tokens should be invalidated after use or logout.

Protect Against XSS and CSRF

Clean every input.
Make use of the CSP (content security policy).
When using cookies, use CSRF tokens.

Conclusion

JWT tokens are an effective tool for API connectivity and contemporary web authentication. They do, however, carry a lot of responsibility.

In addition to this, JWTs can be used for data theft, impersonation, and illegal access if they are improperly set or implemented. From safe signing and validation to storage and expiration, developers need to make sure that best practices are adhered to. JWTs offer a quick, safe, and scalable way to manage user identification across apps when mitigation is done correctly.

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