Transporting access tokens from resource owner password grant flow as cleartext allowed

Issue ID: v3-global-securityscheme-oauth2-ropg-clear

Average severity: Minimal

Description

One or more global security schemes in the API allows to set security requirements that accept access tokens from resource owner password grant flow in OAuth2 authentication, sent in cleartext over an unencrypted channel. Attackers can easily intercept API calls and retrieve the unencrypted tokens. They can then use the tokens to make other API calls.

This flow has been deprecated by OAuth Best Current Practice and must not be used.

This is a potential risk, because the definition is in security schemes. However, it easily turns into an actual risk when the unsafe method is used in a security requirement.

For more details, see the OpenAPI Specification.

Example

The following is an example of how this type of risk could look in your API definition:

{  
    "servers": [
        {
            "url": "http://my.api.server.com/",
            "description": "API server"
        }
    ],
    // ...  
    "components": {
        "securitySchemes": {
            "OAuth2": {
                "type": "oauth2",
                "flows": {
                    "password": {
                        "scopes": {
                            "write": "modify objects in your account",
                            "read": "read objects in your account"
                        },
                        "tokenUrl": "https://example.com/oauth/token" 
                    }
                }
            }
        }
    }
}

Possible exploit scenario

Attackers can intercept the access tokens simply by listening to the network traffic in a public WiFi network. They could also use a traffic logging tool on a smartphone, computer, or browser, or sniff the traffic in the network to get the tokens.

The resource owner password grant flow in OAuth2 is highly dangerous, because it exposes the credentials of the resource owner to the client. Even in the best case, this expands the attack surface and also normalizes insecure behavior (entering your credentials somewhere else than the authorization server).

Remediation

Set all server objects to HTTPS so that all traffic is encrypted, and do not use resource owner password grant flow in OAuth 2 authentication.

{  
    "servers": [
        {
            "url": "https://my.api.server.com/",
            "description": "API server"
        }
    ],
    // ...  
    "components": {
        "securitySchemes": {
            "OAuth2": {
                "type": "oauth2",
                "flows": {
                    "authorizationCode": {
                        "scopes": {
                            "write": "modify objects in your account",
                            "read": "read objects in your account"
                        },
                        "authorizationUrl": "https://example.com/oauth/authorize",
                        "tokenUrl": "https://example.com/oauth/token" 
                    }
                }
            }
        }
    },
    // ...
    "security": [
        {
        "OAuth2": [
                "write",
                "read"
            ]
        }
    ]
}