CVE-2020-5300

In Hydra (an OAuth2 Server and OpenID Certified™ OpenID Connect Provider written in Go), before version 1.4.0+oryOS.17, when using client authentication method 'private_key_jwt' [1], OpenId specification says the following about assertion `jti`: "A unique identifier for the token, which can be used to prevent reuse of the token. These tokens MUST only be used once, unless conditions for reuse were negotiated between the parties". Hydra does not check the uniqueness of this `jti` value. Exploiting this vulnerability is somewhat difficult because: - TLS protects against MITM which makes it difficult to intercept valid tokens for replay attacks - The expiry time of the JWT gives only a short window of opportunity where it could be replayed This has been patched in version v1.4.0+oryOS.17

In Hydra (an OAuth2 Server and OpenID Certified™ OpenID Connect Provider written in Go), before version 1.4.0+oryOS.17, when using client authentication method 'private_key_jwt' [1], OpenId specification says the following about assertion `jti`: "A unique identifier for the token, which can be used to prevent reuse of the token. These tokens MUST only be used once, unless conditions for reuse were negotiated between the parties". Hydra does not check the uniqueness of this `jti` value. Exploiting this vulnerability is somewhat difficult because: - TLS protects against MITM which makes it difficult to intercept valid tokens for replay attacks - The expiry time of the JWT gives only a short window of opportunity where it could be replayed This has been patched in version v1.4.0+oryOS.17

Authentication Bypass in hydra in github.com/ory/hydra

### Impact When using client authentication method "private_key_jwt" [1], OpenId specification says the following about assertion `jti`: > A unique identifier for the token, which can be used to prevent reuse of the token. These tokens MUST only be used once, unless conditions for reuse were negotiated between the parties Hydra does not seem to check the uniqueness of this `jti` value. Here is me sending the same token request twice, hence with the same `jti` assertion, and getting two access tokens: ``` $ 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"} ``` ### Severity We rate the severity as medium because the following reasons make it hard to replay tokens without the patch: - TLS protects against MITM which makes it difficult to intercept valid tokens for replay attacks - The expiry time of the JWT gives only a short window of opportunity where it could be replayed ### Patches This will be patched with v1.4.0+oryOS.17 ### Workarounds Two workarounds have been identified: - Do not allow clients to use `private_key_jwt` - Use short expiry times for the JWTs ### References 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

En Hydra (un OAuth2 Server y OpenID Certified™ OpenID Connect Provider escrito en Go), versiones anteriores a 1.4.0+oryOS.17, cuando se usa el método de autenticación del cliente `private_key_jwt` [1], la especificación OpenId dice lo siguiente sobre la afirmación `jti`: "Un identificador único para el token, que puede ser usado para impedir la reutilización del token. Estos tokens DEBEN solo ser usados una vez, a menos que las condiciones de reutilización sean negociadas entre las partes". Hydra no comprueba la exclusividad de este valor de 'jti'. Una explotación de esta vulnerabilidad es algo difícil porque: - TLS protege contra ataques de tipo MITM, lo que hace que sea difícil interceptar tokens válidos para ataques de repetición - El tiempo de expiración del JWT ofrece solo una pequeña ventana oportunidad para que pueda reproducirse Esto ha sido parcheado en la versión v1 .4.0+oryOS.17