The Fission Environment CRD exposed spec.runtime.podSpec and spec.builder.podSpec fields that were merged directly into Kubernetes pod specs without filtering critical security-related fields such as hostNetwork, hostPID, hostIPC, privileged containers, and serviceAccountName. This allowed a namespace user with create/update permissions on environments.fission.io to create pods with elevated privileges, enabling host filesystem and network access, and potential node compromise. The vulnerability was addressed in pull request #3391 and released in Fission v1.24.0 by implementing an admission denylist that blocks these fields and sanitizing pod specs during merge. The fix also extended webhook validation to cover update operations, closing bypass avenues.

An attacker with create/update permissions on the Fission Environment CRD could deploy pods with host network, host PID, and privileged container settings, enabling them to escape container isolation and compromise the Kubernetes node. This includes access to the host filesystem, network, container runtime socket, and cloud metadata credentials, potentially leading to full node compromise and cluster-wide takeover.

A fix is available in Fission version 1.24.0. This update implements an admission denylist that rejects Environment CRD pod specs containing hostNetwork, hostPID, hostIPC, privileged containers, and other dangerous settings. It also sanitizes these fields during pod spec merging to prevent bypass. Users should upgrade to v1.24.0 or later to mitigate this vulnerability. Prior to upgrading, restricting create/update RBAC permissions on environments.fission.io can reduce risk.