Do not allow local urls in Kubernetes form

Use existing `public_url` validation to block various local urls. Note
that this validation will allow local urls if the "Allow requests to the
local network from hooks and services" admin setting is enabled.

Block KubeClient from using local addresses

It will also respect `allow_local_requests_from_hooks_and_services` so
if that is enabled KubeClinet will allow local addresses

app/models/clusters/platforms/kubernetes.rb

@@ -41,7 +41,7 @@ module Clusters
       validate :no_namespace, unless: :allow_user_defined_namespace?
 
       # We expect to be `active?` only when enabled and cluster is created (the api_url is assigned)
-      validates :api_url, url: true, presence: true
+      validates :api_url, public_url: true, presence: true
       validates :token, presence: true
       validates :ca_cert, certificate: true, allow_blank: true, if: :ca_cert_changed?
 

changelogs/unreleased/security-kubernetes-local-ssrf.yml

+---
+title: Block local URLs for Kubernetes integration
+merge_request:
+author:
+type: security

lib/gitlab/kubernetes/kube_client.rb

@@ -82,6 +82,8 @@ module Gitlab
       def initialize(api_prefix, **kubeclient_options)
         @api_prefix = api_prefix
         @kubeclient_options = kubeclient_options.merge(http_max_redirects: 0)
+
+        validate_url!
       end
 
       def create_or_update_cluster_role_binding(resource)
@@ -118,6 +120,12 @@ module Gitlab
 
       private
 
+      def validate_url!
+        return if Gitlab::CurrentSettings.allow_local_requests_from_hooks_and_services?
+
+        Gitlab::UrlBlocker.validate!(api_prefix, allow_local_network: false)
+      end
+
       def cluster_role_binding_exists?(resource)
         get_cluster_role_binding(resource.metadata.name)
       rescue ::Kubeclient::ResourceNotFoundError

spec/lib/gitlab/kubernetes/kube_client_spec.rb

@@ -50,6 +50,36 @@ describe Gitlab::Kubernetes::KubeClient do
     end
   end
 
+  describe '#initialize' do
+    shared_examples 'local address' do
+      it 'blocks local addresses' do
+        expect { client }.to raise_error(Gitlab::UrlBlocker::BlockedUrlError)
+      end
+
+      context 'when local requests are allowed' do
+        before do
+          stub_application_setting(allow_local_requests_from_hooks_and_services: true)
+        end
+
+        it 'allows local addresses' do
+          expect { client }.not_to raise_error
+        end
+      end
+    end
+
+    context 'localhost address' do
+      let(:api_url) { 'http://localhost:22' }
+
+      it_behaves_like 'local address'
+    end
+
+    context 'private network address' do
+      let(:api_url) { 'http://192.168.1.2:3003' }
+
+      it_behaves_like 'local address'
+    end
+  end
+
   describe '#core_client' do
     subject { client.core_client }
 

spec/models/clusters/platforms/kubernetes_spec.rb

@@ -98,6 +98,22 @@ describe Clusters::Platforms::Kubernetes, :use_clean_rails_memory_store_caching
 
         it { expect(kubernetes.save).to be_truthy }
       end
+
+      context 'when api_url is localhost' do
+        let(:api_url) { 'http://localhost:22' }
+
+        it { expect(kubernetes.save).to be_falsey }
+
+        context 'Application settings allows local requests' do
+          before do
+            allow(ApplicationSetting)
+              .to receive(:current)
+              .and_return(ApplicationSetting.build_from_defaults(allow_local_requests_from_hooks_and_services: true))
+          end
+
+          it { expect(kubernetes.save).to be_truthy }
+        end
+      end
     end
 
     context 'when validates token' do