fix(template): add to dissallowed functions (#4848)

brandtkeller · web-flow · commit cedec4dcbae3 · 2026-04-24T15:34:02.000Z
Signed-off-by: Brandt Keller &lt;brandt.keller@defenseunicorns.com&gt;
diff --git a/COMMUNITY.md b/COMMUNITY.md
@@ -6,7 +6,7 @@ Come say hello! We're on the OpenSSF/Kubernetes Slack workspaces and hold a comm
 |-------------------------------|---------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------------|
 | Website                       | [zarf.dev](https://zarf.dev)                                                                                                                                                                            |
 | Docs Website                  | [docs.zarf.dev](https://docs.zarf.dev)                                                                                                                                                                  |
-| OpenSSF Slack Invite          | [slack.openssf.org](http://slack.openssf.org/)                                                                                                                                                          |
+| OpenSSF Slack Invite          | [slack.openssf.org](https://slack.openssf.org/)                                                                                                                                                          |
 | OpenSSF Slack Channel         | [#zarf](https://openssf.slack.com/archives/C07AKUMBDMJ)                                                                                                                                                 |
 | Kubernetes Slack Invite       | [kubernetes.slack.com/](https://kubernetes.slack.com/)                                                                                                                                                  |
 | Kubernetes Slack Channel      | [#zarf](https://kubernetes.slack.com/archives/C03B6BJAUJ3)                                                                                                                                              |
diff --git a/src/internal/template/template.go b/src/internal/template/template.go
@@ -160,11 +160,13 @@ func ApplyToFile(ctx context.Context, src, dst string, objs Objects) error {
 
 // Source: https://github.com/helm/helm/blob/main/pkg/engine/funcs.go#L45
 // SPDX-License-Identifier: Apache 2.0
-// Minor edits: revised var names
+// Minor edits: revised var names, getHostByName removal
 func funcMap() ttmpl.FuncMap {
 	m := sprig.TxtFuncMap()
 	delete(m, "env")
 	delete(m, "expandenv")
+	// live DNS lookup could leak templating context
+	delete(m, "getHostByName")
 	extras := ttmpl.FuncMap{
 		"toToml":        toTOML,
 		"fromToml":      fromTOML,
diff --git a/src/internal/template/template_test.go b/src/internal/template/template_test.go
@@ -422,6 +422,41 @@ func TestApply(t *testing.T) {
 	}
 }
 
+// TestFuncMap_UnsafeSprigFunctionsRemoved pins the set of sprig functions
+// deliberately stripped from the template engine. Re-adding any of these
+// reintroduces a host-side-effect or exfiltration channel that Zarf packages
+// (including untrusted ones) must not reach.
+func TestFuncMap_UnsafeSprigFunctionsRemoved(t *testing.T) {
+	m := funcMap()
+	for _, name := range []string{"env", "expandenv", "getHostByName"} {
+		_, present := m[name]
+		require.False(t, present, "sprig function %q must not be registered in funcMap", name)
+	}
+}
+
+// TestApply_UnsafeSprigFunctionsRejected verifies that templates invoking the
+// stripped functions fail at parse time rather than silently skipping or
+// executing. This is the end-to-end regression guard for the funcMap stripping.
+func TestApply_UnsafeSprigFunctionsRejected(t *testing.T) {
+	tests := []struct {
+		name string
+		tmpl string
+	}{
+		{name: "env", tmpl: `{{ env "PATH" }}`},
+		{name: "expandenv", tmpl: `{{ expandenv "$PATH" }}`},
+		{name: "getHostByName", tmpl: `{{ getHostByName "localhost" }}`},
+	}
+	for _, tt := range tests {
+		t.Run(tt.name, func(t *testing.T) {
+			ctx := context.Background()
+			_, err := Apply(ctx, tt.tmpl, Objects{})
+			require.Error(t, err)
+			require.Contains(t, err.Error(), tt.name)
+			require.Contains(t, err.Error(), "not defined")
+		})
+	}
+}
+
 func TestApplyToFile(t *testing.T) {
 	tests := []struct {
 		name     string
