Apache Pulsar: Function trigger publishes to the input topic without checking the caller's produce permission

Summary

The Pulsar Functions Worker provides a REST API endpoint for triggering a function, which publishes a caller-supplied value to one of the function's configured input topics. The Functions Worker performs this publish with its own broker client, which authenticates with the Worker's configured broker-client credentials rather than the credentials of the API caller.

When authorization is enabled, in Apache Pulsar 2.4.0 and later versions, the trigger endpoint checks only that the caller is authorized to perform function operations in the function's namespace. It does not check that the caller is authorized to produce to the input topic that the message is published to. Versions before 2.4.0 do not perform a caller authorization check for the trigger endpoint at all. Function input topics are not restricted to the function's own tenant or namespace, and registering a function does not require produce permission on its input topics.

As a result, an authenticated user who is authorized to manage functions in a namespace, for example a role granted the functions permission on that namespace, can cause the Functions Worker to publish messages with caller-controlled content to a topic that the user is not authorized to produce to, including topics in other tenants. These messages are published under the identity of the Functions Worker. The issue does not require any function instance to be running or any function code to be executed. It requires that the Functions Worker's broker-client identity is itself authorized to produce to the target topic and, in Apache Pulsar 2.3.0 and later versions, to list the subscriptions of the target topic, as is the case when that identity is a superuser. The impact is on the integrity of the data in the affected topics: consumers of those topics may receive messages from a user who is not permitted to publish them. This concerns the Functions Worker REST API as called by an external, authenticated client; it does not change the security model for function code, which must be fully trusted.

In fixed versions, when authorization is enabled, triggering a function additionally requires the caller to be authorized to produce to the selected input topic before any message is published.

This issue affects Apache Pulsar versions from 2.0.0-rc1-incubating 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 of Apache Pulsar 2.4.0 and later versions with authorization enabled who cannot upgrade immediately can limit the permission to manage functions to trusted roles. Users of versions before 2.4.0 should restrict access to the Functions Worker REST API to trusted callers, because in these versions the trigger endpoint does not check the caller's permission to manage functions.