Fission builder pods auto-mount the fission-builder ServiceAccount token in the user-supplied builder container

Summary

Fission builder pods were created with ServiceAccountName: fission-builder and no AutomountServiceAccountToken: false, so the kubelet auto-mounted the service-account token into every container in the pod — including the user-supplied builder image.

Details

The user controls the builder container image, command, and podspec through Environment.spec.builder.image / .container / .podspec. With the SA token auto-mounted at /var/run/secrets/kubernetes.io/serviceaccount/token inside that container, any code running there inherited the fission-builder identity. The fission-builder SA holds namespace-wide get on secrets and configmaps (pkg/utils/serviceaccount.go), so the user-controlled builder container could read every Secret in the builder namespace by name.

This is the buildermgr sibling of GHSA-85g2-pmrx-r49q (CVE-2026-46617), whose fix suppressed the SA-token automount on function runtime pods but did not cover the structurally identical primitive in pkg/buildermgr/envwatcher.go.

Impact

A subject with create/update on Environment CRDs in a namespace observed by the buildermgr could read every Secret and ConfigMap in the builder namespace via the auto-mounted fission-builder token.

Fix

Fixed in #3390 and released in v1.24.0. In createBuilderDeployment:

• Set pod-level AutomountServiceAccountToken=false on the initial PodSpec and add the projected fetcher SA-token volume.
• Re-clamp AutomountServiceAccountToken=false after every MergePodSpec call so a user-supplied podspec cannot restore the kubelet automount.
• Mount the token via a projected volume on the fetcher sidecar only, so the legitimate build → archive-upload flow keeps its cluster API access.

Reuses the projected-volume helpers from pkg/executor/util/satoken.go introduced by the GHSA-85g2-pmrx-r49q fix.

Behavioural change

The user-supplied builder container no longer receives an auto-mounted SA token. The fetcher sidecar still gets its token via a projected volume.