The Apache Pulsar WebSocket service allows a WebSocket consumer to configure a dead letter policy through query parameters of the consumer endpoint, including the deadLetterTopic parameter that names the topic to which messages are written after the maximum number of redeliveries is exceeded. When authorization is enabled, the WebSocket service checks only that the connecting user holds the CONSUME permission on the subscribed topic. It does not check whether the user holds the PRODUCE permission on the topic named in deadLetterTopic. The dead letter messages are then written by the WebSocket service using its own broker client identity rather than the identity of the connecting user.
As a result, an authenticated user who holds the CONSUME permission on at least one topic can cause messages to be written to a topic of their choosing in any existing namespace, including namespaces belonging to other tenants, provided the role used by the WebSocket service to connect to the brokers is authorized to produce to that topic and the topic accepts a producer that registers no schema. The dead letter producer created by the WebSocket service registers no schema, so it is rejected when the target topic has a schema and schema validation is enforced for that topic or its namespace; this setting is not enabled by default. The same user is refused when attempting to produce to that topic directly. Where automatic topic creation is enabled, which is the default, the named topic is created if it does not already exist. The issue can only be triggered when the WebSocket service is enabled, either in the broker (webSocketServiceEnabled, which is disabled by default) or as a standalone WebSocket proxy.
The impact is unauthorized injection of messages into topics the user is not permitted to produce to. The user can determine the content of the injected messages when they also control the messages on the subscribed topic. The issue does not allow reading, modifying or deleting existing messages in the target topic. Injected messages carry the dead letter message properties and a dead letter producer name, so they can be distinguished from messages produced normally; however, the values of these properties are not authenticated and should not be relied upon to establish the origin of a message. Whether an injected message has further consequences depends on how the applications consuming the target topic process it. Repeated injection also consumes storage and backlog capacity in the target namespace.
This issue affects Apache Pulsar versions from 2.3.0 before 4.0.14 and from 4.1.0 before 4.2.5.
- 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 do not require the WebSocket service should disable it. Where the WebSocket service is required, restricting network access to it and limiting the permissions granted to the role the WebSocket service uses to connect to the brokers to the namespaces WebSocket clients are intended to access reduces the exposure.
Weakness
The product performs an authorization check when an actor attempts to access a resource or perform an action, but it does not correctly perform the check.
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.