Kubeflow Pipelines enables users to build and deploy portable, scalable machine learning workflows. Prior to 2.16.1, the multi-user API server treats the empty namespace used by shared or global pipelines as an authorization exception for modification and deletion operations. An authenticated user can modify or delete shared pipeline definitions and versions without the required Kubernetes RBAC permissions, compromising their integrity and availability. Read-only access to shared pipelines remains intentional, single-user deployments intentionally bypass multi-user checks, and execution of a modified pipeline is a conditional downstream consequence. The separate shared-pipeline multipart upload authorization path is outside this advisory and is not remediated by version 2.16.1. This issue is fixed in version 2.16.1.

Affected: Go: github.com/kubeflow/pipelines

## Summary

In multi-user mode, the Kubeflow Pipelines API server skipped authorization checks for shared/global pipelines with an empty namespace. This exception applied to write and delete operations as well as reads, allowing an authenticated user to modify or delete shared pipelines without the required Kubernetes RBAC permissions.

## Impact

Unauthorized modification compromises the integrity of shared pipeline definitions and versions. Unauthorized deletion can make shared pipelines unavailable.

Execution of a modified pipeline can cause attacker-controlled workload behavior, but this is a conditional downstream consequence requiring the modified pipeline to be executed. Modification alone does not demonstrate immediate worker code execution.

Reading shared pipelines is intentionally permitted and remains permitted after the fix. Consequently, access to shared pipeline configuration does not establish an additional confidentiality impact from this write-authorization defect. The confidentiality metric is None; the integrity and availability metrics reflect unauthorized modification and deletion of shared pipelines.

The affected authorization boundary is shared pipelines in multi-user deployments. Single-user deployments intentionally bypass these multi-user authorization checks.

## Patches

Fixed by [kubeflow/pipelines#13288](https://github.com/kubeflow/pipelines/pull/13288), with the fix included in 2.16.1.

Read-only operations on shared pipelines remain allowed…