CVE-2026-88979: Kubeflow Pipelines: Unauthenticated SSRF vulnerability in Kubeflow Pipelines TensorBoard proxy

Kubeflow Pipelines enables users to build and deploy portable, scalable machine learning workflows. From 2.17.0 until 2.18.0, the TensorBoard proxy token introduced by the incomplete remediation for CVE-2026-54745 uses MINIOSECRETKEY as its HMAC secret, whose bundled default is publicly known. In an authorization-disabled deployment using that default, an unauthenticated attacker can forge a token containing a chosen viewerName and namespace; the proxy constructs the destination from the viewerName plus the -service suffix, the namespace, and the configured cluster domain, then reads responses on port 80 under the /tensorboard/<viewer>/ path. Resource-name validation and path-traversal rejection remain enforced, authorization-enabled deployments still check access to the selected namespace, and unrestricted metadata access, writes, or service disruption are not established. This issue is fixed in version 2.18.0.