CVE-2026-50545: Fission Environment CRD PodSpec Injection Leading to Node Escape and Cluster Takeover

Summary

A stronger framing of the same root cause as GHSA-gx55-f84r-v3r7: the Environment.spec.runtime.podSpec / spec.builder.podSpec passthrough lacked validation, and MergePodSpec propagated dangerous fields into the generated pods.

Details

Three independent flaws compounded:

1. Validate gap. pkg/apis/core/v1/validation.go::Environment.Validate checked only container naming conventions, never hostPID/hostIPC/hostNetwork/hostPath/privileged.
2. UPDATE bypass. The pkg/webhook/environment.go kubebuilder marker registered verbs=create only. A tenant could kubectl apply a clean Environment and then kubectl patch in the dangerous fields — the webhook was never called.
3. Merge propagation. pkg/executor/util/merge.go::MergePodSpec unconditionally forwarded HostPID, HostIPC, HostNetwork, Volumes (including hostPath), SecurityContext, and ServiceAccountName into the Deployments

generated by poolmgr / newdeploy / buildermgr.

A kubectl apply plus a follow-up kubectl patch caused poolmgr to schedule a privileged pod with a host-root mount within roughly 20 seconds. From that pod the cluster CA private key was readable, allowing the attacker to sign arbitrary kubelet certificates and achieve full cluster takeover.

Impact

environments.fission.io create/update RBAC is escalated to node escape and, via the readable cluster CA key, full cluster takeover.

Fix

Fixed in #3391 (with the companion buildermgr SA-token fix in #3390) and released in v1.24.0. Each enumerated flaw is addressed:

1. Validate — ValidatePodSpecSafety is called from Environment.Validate for both Runtime.PodSpec and Builder.PodSpec.
2. UPDATE bypass — the webhook marker is extended to verbs=create;update; chart and envtest manifests are aligned.
3. Merge propagation — host namespaces, ServiceAccountName, and hostPath volumes are stripped at the merge layer; per-container privileged/allowPrivilegeEscalation and dangerous capabilities are sanitized.

See GHSA-gx55-f84r-v3r7 for the detailed fix — both advisories close to the same commit.

Duplicate handling

This advisory and GHSA-gx55-f84r-v3r7 were reported separately but close to the same code fix. Both are published to acknowledge each reporter's contribution and to keep the public CVE record clear about the multi-layer nature of the issue.