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The Hacker's Guide to JWT Security - Patrycja Wegrzynowicz
Learn the essential security measures to protect your JSON Web Tokens (JWTs) from vulnerabilities and misuse, including key management, token verification, and anti-XSS practices to ensure secure stateless sessions and data exchange.
- JSON Web Tokens (JWTs) by default do not provide any built-in feature to revoke token or expire tokens.
- Never trust clients and always verify signatures.
- Always require a specific algorithm and key during verification to prevent token misuse.
- HMAC with SHA is a widely used algorithm in JWTs, but it’s not recommended due to its potential vulnerabilities.
- JWTs can be easily cracked, and a single compromised token can compromise the entire system.
- It’s essential to use HTTPS from a browser to the server side, and always verify the algorithm used to generate the token.
- Always check for vulnerabilities in libraries and frameworks used to implement JWTs.
- Keys should be kept secret and never shared, and a single compromised key can result in massive token misuse.
- It’s recommended to use asymmetric encryption, such as RSA, to generate JWTs, but it’s not widely supported.
- JWTs can be used to create a stateless session mechanism, but this also provides an opportunity for attackers to steal tokens.
- Always verify if the algorithm provided in a token is the one used on the server side.
- Tokens can be stolen using cross-site scripting (XSS) attacks or injected attacks.
- A shared key used on all servers can be compromised, allowing attackers to steal tokens.
- It’s essential to understand the library in use and apply anti-XSS practices.
- A fool with a tool is only a fool; it’s essential to know the library and its limitations.
- JWTs can be used to bypass same origin policy, making it possible to access information from other domains.
- It’s recommended to use a cookie as a storage mechanism for JWTs instead of using only cookies or headers.
- The recommended key length for HMAC with SHA is a minimum of 2K bits, but keys should be as long as the length of the hash.
- Always check for updates and maintenance cycles of libraries used to implement JWTs.
- Keys should be changed periodically to prevent token misuse.
- Always require proper verification of signatures and algorithm used during token generation.