The Apache Pulsar broker admin REST API provides endpoints to read, set and remove the topic-level entry filter policy of a topic. For persistent topics these endpoints check that the caller is authorized for the entry filters topic policy operation. The corresponding endpoints for non-persistent topics (/admin/v2/non-persistent/{tenant}/{namespace}/{topic}/entryFilters) do not perform this authorization check. The only authorization check these endpoints perform is an indirect lookup permission check, made while the topics partition metadata is retrieved; it is present in all affected versions.
As a result, when authentication and authorization are enabled, an authenticated user who has been granted produce or consume permission on a non-persistent topic, or on its namespace, but not permission to manage the topics policies can read, replace or remove the topic-level entry filter policy of that topic. These operations should be restricted to users with the tenant admin role or the superuser role. This impact analysis assumes that Pulsar has been configured with the default authorization provider. For custom authorization providers, the impact could be slightly different.
The practical impact is limited by two broker configuration requirements, neither of which is met by default:
- Entry filters must have been installed by the operator. Entry filter implementations are loaded only at broker startup from the brokers entry filters directory, which is empty by default. A request can only select among entry filters the operator has already deployed; setting any other filter name is rejected. The issue does not allow a caller to install or load entry filter code or to run arbitrary code in the broker.
- Topic-level entry filter policies must be allowed to override the broker-level configuration (allowOverrideEntryFilters, which is disabled by default). When this setting is disabled, the topic-level entry filter policy has no effect on message dispatch.
In deployments where both conditions are met, an unauthorized user can remove the topic-level entry filter policy of a non-persistent topic, for example one used to restrict which messages are delivered to consumers, or apply a different installed entry filter that withholds messages from subscriptions of that topic. Removing it makes the topic fall back to the namespace-level or broker-level entry filters, which are not removed. A changed policy affects only subscription dispatchers created after the change, for example for new subscriptions or when a subscription is re-created after all of its consumers have disconnected; dispatchers that already exist keep the entry filters they were created with. Because non-persistent topics do not store messages, messages withheld by an entry filter are not delivered. Reading the policy discloses only the names of the configured entry filters. The issue does not allow reading message contents, and entry filters cannot modify message payloads. Persistent topics and namespace-level entry filter policies are not affected. Apache Pulsar versions before 3.3.0 are not affected, because in those versions the entry filters topic policy check is made in code shared by the persistent and non-persistent endpoints.
This issue affects Apache Pulsar versions from 3.3.0 before 4.0.14 and from 4.1.0 before 4.2.5.
- 3.3.x and 4.0.x version users should upgrade to at least 4.0.14.
- 4.1.x and 4.2.x version users should upgrade to at least 4.2.5.
Users operating versions prior to those listed above should upgrade to the aforementioned patched versions or newer versions.
The currently supported Apache Pulsar release lines are 4.0.x and 5.0.x. The supported versions schedule is available at https://pulsar.apache.org/contribute/release-policy/.
Users who cannot upgrade immediately and have deployed entry filters should keep allowOverrideEntryFilters at its default value of false, so that topic-level entry filter policies do not affect message dispatch.
Weakness
The product does not perform an authorization check when an actor attempts to access a resource or perform an action.
Potential Mitigations
- Divide the product into anonymous, normal, privileged, and administrative areas. Reduce the attack surface by carefully mapping roles with data and functionality. Use role-based access control (RBAC) [REF-229] to enforce the roles at the appropriate boundaries.
- Note that this approach may not protect against horizontal authorization, i.e., it will not protect a user from attacking others with the same role.
- Use a vetted library or framework that does not allow this weakness to occur or provides constructs that make this weakness easier to avoid.
- For example, consider using authorization frameworks such as the JAAS Authorization Framework [REF-233] and the OWASP ESAPI Access Control feature [REF-45].
- For web applications, make sure that the access control mechanism is enforced correctly at the server side on every page. Users should not be able to access any unauthorized functionality or information by simply requesting direct access to that page.
- One way to do this is to ensure that all pages containing sensitive information are not cached, and that all such pages restrict access to requests that are accompanied by an active and authenticated session token associated with a user who has the required permissions to access that page.