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Testing, tweaking and cracking JSON Web Tokens (JWT)

What is JSON Web Token?

JWT (JSON Web Token) is an open standard (RFC 7519) that defines a compact and self-contained way for securely transmitting information between parties as a JSON object. This information can be verified and trusted because it is digitally signed. JWTs can be signed using a secret (with the HMAC algorithm) or a public/private key pair using RSA or ECDSA.

In this post, we will see how to test, tweak, and try to crack JWTs. There are few open-source libraries that we can use. One such utility is https://github.com/ticarpi/jwt_tool which is a toolkit for testing, tweaking, and cracking JSON Web Tokens.

This tool is written in Python 3 (version 3.6+).

Its functionality includes:

  • Checking the validity of a token
  • Testing for known exploits:
  • (CVE-2015–2951) The  signature-bypass vulnerability
  • (CVE-2016–10555) The  public key mismatch vulnerability
  • (CVE-2018–0114)  vulnerability
  • Scanning for misconfigurations or known weaknesses
  • Fuzzing claim values to provoke unexpected behaviors
  • Testing the validity of a secret/key file/Public Key/JWKS key
  • Identifying  via a High-speed 
  • Forging new token header and payload contents and creating a new signature with the key or via another attack method
  • Timestamp tampering
  • RSA and ECDSA key generation, and reconstruction (from JWKS files)
  • …and lots more!

You can visit the repository on github and get the instructions on github.

Happy Coding!!!

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