The Apache Pulsar broker admin REST API provides a truncate operation for persistent topics (DELETE /admin/v2/persistent/{tenant}/{namespace}/{topic}/truncate). Truncating a topic moves all subscription cursors of the topic to the end of the topic and deletes the topic's inactive ledgers. Truncating a non-partitioned topic, or a single partition addressed by its partition name, correctly requires the tenant admin role or the superuser role. When the operation is requested for the name of a partitioned topic, the broker does not apply this tenant admin check to the caller. Instead, it truncates each partition using the broker's own internal admin client, which authenticates with the broker's configured client credentials rather than the caller's identity. Each per-partition truncate request is still checked for the tenant admin role or the superuser role, but against the broker's internal identity instead of the caller. The partitions are therefore truncated only when the broker's configured client role is a superuser or an admin of the target tenant, which is the usual configuration when authorization is enabled.

As a result, when that condition holds, an authenticated user who is not a tenant admin can truncate any partitioned topic on which the user has lookup permission. Caller authentication and lookup permission alone are not sufficient: if the broker's internal identity lacks tenant admin or superuser authorization for the target tenant, the per-partition requests are rejected. With the default authorization provider, lookup permission is granted by produce or consume permission on the topic or its namespace. A user with no permissions on the topic cannot trigger the issue. This impact analysis assumes that Pulsar has been configured with the default authorization provider. For custom authorization providers, the impact could be different.

Truncating a partitioned topic this way moves the cursors of all subscriptions on every partition to the end of the topic, so any unacknowledged backlog is skipped and is no longer delivered to consumers. It also deletes eligible older ledgers of each partition regardless of the namespace's configured retention policy, so messages stored in those ledgers can be permanently lost. The ledger currently being written is not deleted by the truncate operation. The issue does not allow reading message contents or changing permissions or configuration, and it does not give access to topics on which the user has no lookup permission.

This issue affects Apache Pulsar versions from 2.8.0 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 can reduce exposure by restricting network access to the broker's admin REST API (/admin/v2) to trusted administrative clients.