Fission: MessageQueueTrigger scaler manager materializes Secret values into Deployment envvars and accepts arbitrary user PodSpec

Summary

The Fission MessageQueueTrigger (MQT) scaler controller exposed two privilege-escalation primitives to any subject able to create MQTs in a namespace.

Details

1. Secret materialization. getEnvVarlist in pkg/mqtrigger/scalermanager.go read the Secret named in Spec.Secret using the controller's cluster-wide secrets/get RBAC and emitted each key as a literal EnvVar.Value, copying the plaintext secret content into the connector Deployment's pod template. A subject holding messagequeuetriggers/create but not secrets/get could exfiltrate any Secret in the namespace by pointing an MQT at it.

2. PodSpec injection. Spec.PodSpec was merged into the controller-built connector PodSpec via util.MergePodSpec with no allowlist on which fields could come from the user. An MQT could substitute Containers[].Image (run any image), override Command/Args, inject Env, add VolumeMounts + Volumes, override ServiceAccountName, and set HostNetwork/HostPID/HostIPC — turning messagequeuetriggers/create into effective deployments/create with an arbitrary image and service account.

Impact

A tenant with only messagequeuetriggers.fission.io/create in a namespace could read any Secret in that namespace and run an arbitrary container image under an arbitrary service account, escalating well beyond their intended RBAC.

Fix

Fixed in #3367 and released in v1.24.0.

• getEnvVarlist now emits EnvVar.ValueFrom.SecretKeyRef so the connector pod resolves values at start time under its own service account. The secret values are never written into the Deployment object and never logged.
• A new allowlist, MergeAllowedPodSpecFields (pkg/executor/util/merge_allowlist.go), accepts only NodeSelector, Tolerations, Affinity, RuntimeClassName, and per-container Resources. All other user-supplied fields are dropped at the controller layer, and the validating webhook rejects every populated non-allowlisted field with a clear error. The webhook and the merge helper share a single canonical DisallowedPodSpecFields enumeration so they cannot drift.

Behavioural change

MQT authors that previously overrode the connector image, command, args, env, volumes, service account, or host namespaces via Spec.PodSpec will see those fields rejected at admission (or silently dropped if the webhook is disabled). Allowlisted fields flow through unchanged.