Fission: Cross-namespace Package read via unvalidated PackageRef in Function admission webhook

Summary

A Fission Function spec carries three reference types — Secret, ConfigMap, and Package. The first two were namespace-validated by the admission webhook; PackageRef.Namespace was not.

Details

A tenant with functions.fission.io/create in their own namespace could set spec.package.packageref.namespace to any other namespace. When the function is invoked, the fetcher sidecar reads the victim Package using the fission-fetcher service account's namespace-wide get packages permission and writes its contents to /userfunc/deployarchive inside the attacker's pool pod, exposing the victim's source code and any embedded credentials.

The fission-fetcher SA holds get packages in every configured function namespace (granted by charts/fission-all/templates/_function-access-role.tpl), so the namespace check was the only barrier between the attacker and any in-cluster Fission Package.

Impact

A function author in one namespace could read the deployment archive — and therefore the source code and embedded secrets — of any Package in any other namespace.

Fix

Fixed in #3389 and released in v1.24.0.

The admission webhook (pkg/webhook/function.go::Validate) rejects Function.spec.package.packageref.namespace != metadata.namespace. An empty namespace remains accepted (controllers default it to the function's namespace). This shipped together with the EnvironmentRef cross-namespace check (GHSA-cvw6-gfvv-953q).

Behavioural change

Functions that explicitly set spec.package.packageref.namespace to a different namespace are now rejected at admission.