Fission builder accepts arbitrary buildcmd strings from Environment.spec.builder.command, allowing the builder pod to invoke arbitrary executables

Summary

Before the round-1 security sweep, pkg/builder/builder.go passed Environment.spec.builder.command directly into exec.Command(...) after a strings.Fields split, with no validation of the executable path or its arguments. A user who could create or update Environment CRDs in a namespace observed by the buildermgr could thereby point the builder pod at any executable inside the builder image (e.g. /bin/sh -c '...') and execute arbitrary code in the builder pod context.

Affected component

• pkg/builder/builder.go:254 — call site (exec.Command(buildCmd, buildArgs...)).
• pkg/builder/builder.go:106 — input source: buildCmd, buildArgs = strings.Fields(req.BuildCommand)[0], strings.Fields(req.BuildCommand)[1:].

Impact

A subject with create / update privilege on Environment objects could:

1. Cause the builder pod for any package using that environment to execute arbitrary code.
2. Read whatever files the builder pod has access to inside its /packages shared volume (deployment archive payloads for that package).
3. Write arbitrary content into the /packages shared volume, which the fetcher subsequently uploads as the package deployment archive.

The builder pod runs in the user's namespace with the fission-builder SA (not the more-privileged executor SA), so the impact is bounded to that namespace's package contents and the builder pod's own filesystem. PR:H reflects that creating / modifying Environment CRDs is typically restricted to cluster admins or platform operators.

Root cause

pkg/builder/builder.go's build-command parser did not validate the resulting executable path. Although exec.Command does not invoke a shell, it does locate the executable via $PATH, and strings.Fields splitting allowed multiple flags / sub-arguments to be passed.

Fix

Released in v1.23.0:

• PR #3364 (commit 0f45c911) introduces Builder.resolveBuildCommand in pkg/builder/builder.go, which:
  1. Accepts an empty string (treated as the default ).