Strawberry GraphQL: Synchronous permission checks can treat an awaitable authorization result as truthy

Summary

PermissionExtension.resolve() evaluates the return value of has_permission() for truthiness on the synchronous path. supports_sync only classifies a permission as asynchronous when has_permission is declared with async def (via inspect.iscoroutinefunction), so a plain def that returns an awaitable is treated as synchronous. An awaitable is always truthy, so the check passes even when it resolves to False and the protected resolver runs.

The resolve path is chosen by the field resolver, not by the execution method, so any field with a synchronous resolver is affected under both execute_sync() and execute(). Permissions declared with async def has_permission(), or a plain def returning a boolean, are not affected.

Details

The affected code is PermissionExtension.resolve() in strawberry/permission.py. A permission attached to a field whose has_permission is a normal def returning an awaitable reaches this path; the awaitable is never awaited and its truthiness grants access. resolve_async() is not affected because it uses await_maybe().

PoC

import strawberry
from strawberry.permission import BasePermission


class DenyViaAwaitable(BasePermission):
    message = "denied"

    def has_permission(self, source, info, **kwargs):
        async def result():
            return False

        return result()


@strawberry.type
class Query:
    @strawberry.field(permission_classes=[DenyViaAwaitable])
    def secret(self) -> str:
        return "secret"


schema = strawberry.Schema(Query)
print(schema.execute_sync("{ secret }").data)  # {'secret': 'secret'} instead of a permission error

Impact

An application using a custom permission whose has_permission is a normal def returning an awaitable can unintentionally grant access to the protected field. Standard permissions (a def returning a boolean, or an async def) are not affected, so exploitability depends on the application using this specific permission shape.

Fix

The synchronous path now fails closed: if has_permission() returns an awaitable, an error is raised instead of granting access.