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The JSON Web Token Toolkit v2

jwt_tool.py is a toolkit for validating, forging, scanning and tampering JWTs (JSON Web Tokens).

jwt_tool version python version

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Its functionality includes:

Audience

This tool is written for pentesters, who need to check the strength of the tokens in use, and their susceptibility to known attacks. A range of tampering, signing and verifying options are available to help delve deeper into the potential weaknesses present in some JWT libraries.
It has also been successful for CTF challengers - as CTFs seem keen on JWTs at present.
It may also be useful for developers who are using JWTs in projects, but would like to test for stability and for known vulnerabilities when using forged tokens.

Requirements

This tool is written natively in Python 3 (version 3.6+) using the common libraries, however various cryptographic funtions (and general prettiness/readability) do require the installation of a few common Python libraries.
(An older Python 2.x version of this tool is available on the legacy branch for those who need it, although this is no longer be supported or updated)

Installation

Docker

The preferred usage for jwt_tool is with the official Dockerhub-hosted jwt_tool docker image
The base command for running this is as follows:
Base command for running jwt_tool:
docker run -it --network "host" --rm -v "${PWD}:/tmp" -v "${HOME}/.jwt_tool:/root/.jwt_tool" ticarpi/jwt_tool

By using the above command you can tag on any other arguments as normal.
Note that local files in your current working directory will be mapped into the docker container's /tmp directory, so you can use them using that absolute path in your arguments.
i.e.
/tmp/localfile.txt

Manual Install

Installation is just a case of downloading the jwt_tool.py file (or git clone the repo).
(chmod the file too if you want to add it to your $PATH and call it from anywhere.)

$ git clone https://github.com/ticarpi/jwt_tool
$ python3 -m pip install -r requirements.txt

On first run the tool will generate a config file, some utility files, logfile, and a set of Public and Private keys in various formats.

Custom Configs

Colour bug in Windows

To fix broken colours in Windows cmd/Powershell: uncomment the below two lines in jwt_tool.py (remove the "# " from the beginning of each line)
You will also need to install colorama: python3 -m pip install colorama

# import colorama
# colorama.init()

Usage

The first argument should be the JWT itself (unless providing this in a header or cookie value). Providing no additional arguments will show you the decoded token values for review.
$ python3 jwt_tool.py <JWT>
or the Docker base command:
$ docker run -it --network "host" --rm -v "${PWD}:/tmp" -v "${HOME}/.jwt_tool:/root/.jwt_tool" ticarpi/jwt_tool

The toolkit will validate the token and list the header and payload values.

Additional arguments

The many additional arguments will take you straight to the appropriate function and return you a token ready to use in your tests.
For example, to tamper the existing token run the following:
$ python3 jwt_tool.py eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJsb2dpbiI6InRpY2FycGkifQ.aqNCvShlNT9jBFTPBpHDbt2gBB1MyHiisSDdp8SQvgw -T

Many options need additional values to set options.
For example, to run a particular type of exploit you need to choose the eXploit (-X) option and select the vulnerability (here using "a" for the alg:none exploit):
$ python3 jwt_tool.py eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJsb2dpbiI6InRpY2FycGkifQ.aqNCvShlNT9jBFTPBpHDbt2gBB1MyHiisSDdp8SQvgw -X a

Extra parameters

Some options such as Verifying tokens require additional parameters/files to be provided (here providing the Public Key in PEM format):
$ python3 jwt_tool.py eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJsb2dpbiI6InRpY2FycGkifQ.aqNCvShlNT9jBFTPBpHDbt2gBB1MyHiisSDdp8SQvgw -V -pk public.pem

Sending tokens to a web application

All modes now allow for sending the token directly to an application.
You need to specify:

Various responses from the request are displayed:

Common Workflow

Here is a quick run-through of a basic assessment of a JWT implementation. If no success with these options then dig deeper into other modes and options to hunt for new vulnerabilities (or zero-days!).

Recon:

Read the token value to get a feel for the claims/values expected in the application:
$ python3 jwt_tool.py eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJsb2dpbiI6InRpY2FycGkifQ.aqNCvShlNT9jBFTPBpHDbt2gBB1MyHiisSDdp8SQvgw

Scanning:

Run a Playbook Scan using the provided token directly against the application to hunt for common misconfigurations:
$ python3 jwt_tool.py -t https://www.ticarpi.com/ -rc "jwt=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJsb2dpbiI6InRpY2FycGkifQ.bsSwqj2c2uI9n7-ajmi3ixVGhPUiY7jO9SUn9dm15Po;anothercookie=test" -M pb

Exploitation:

If any successful vulnerabilities are found change any relevant claims to try to exploit it (here using the Inject JWKS exploit and injecting a new username):
$ python3 jwt_tool.py -t https://www.ticarpi.com/ -rc "jwt=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJsb2dpbiI6InRpY2FycGkifQ.bsSwqj2c2uI9n7-ajmi3ixVGhPUiY7jO9SUn9dm15Po;anothercookie=test" -X i -I -pc name -pv admin

Fuzzing:

Dig deeper by testing for unexpected values and claims to identify unexpected app behaviours, or run attacks on programming logic or token processing:
$ python3 jwt_tool.py -t https://www.ticarpi.com/ -rc "jwt=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJsb2dpbiI6InRpY2FycGkifQ.bsSwqj2c2uI9n7-ajmi3ixVGhPUiY7jO9SUn9dm15Po;anothercookie=test" -I -hc kid -hv custom_sqli_vectors.txt

Review:

Review any successful exploitation by querying the logs to read more data about the request and :
$ python3 jwt_tool.py -t https://www.ticarpi.com/ -rc "jwt=eyJ0eXAiOiJKV1QiLCJhbGciOiJIUzI1NiJ9.eyJsb2dpbiI6InRpY2FycGkifQ.bsSwqj2c2uI9n7-ajmi3ixVGhPUiY7jO9SUn9dm15Po;anothercookie=test" -X i -I -pc name -pv admin

Help

For a list of options call the usage function: Some options such as Verifying tokens require additional parameters/files to be provided:
$ python3 jwt_tool.py -h

A more detailed user guide can be found on the wiki page.

JWT Attack Playbook - new wiki content!

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Head over to the JWT Attack Playbook for a detailed run-though of what JWTs are, what they do, and a full workflow of how to thoroughly test them for vulnerabilities, common weaknesses and unintended coding errors.

Tips

Regex for finding JWTs in Burp Search
(make sure 'Case sensitive' and 'Regex' options are ticked)
[= ]eyJ[A-Za-z0-9_-]*\.[A-Za-z0-9._-]* - url-safe JWT version
[= ]eyJ[A-Za-z0-9_\/+-]*\.[A-Za-z0-9._\/+-]* - all JWT versions (higher possibility of false positives)

Further Reading