Fix DNS rebinding protection for Outbound Requests

This fixes DNS rebinding protection bypass when allowing an IP address
in Outbound Requests setting.

changelogs/unreleased/security-ssrf-outbound-request.yml

+---
+title: Fix DNS rebinding protection bypass when allowing an IP address in Outbound Requests setting
+merge_request:
+author:
+type: security

lib/gitlab/url_blocker.rb

@@ -49,10 +49,12 @@ module Gitlab
         return [uri, nil] unless address_info
 
         ip_address = ip_address(address_info)
-        return [uri, nil] if domain_allowed?(uri) || ip_allowed?(ip_address, port: get_port(uri))
+        return [uri, nil] if domain_allowed?(uri)
 
         protected_uri_with_hostname = enforce_uri_hostname(ip_address, uri, dns_rebind_protection)
 
+        return protected_uri_with_hostname if ip_allowed?(ip_address, port: get_port(uri))
+
         # Allow url from the GitLab instance itself but only for the configured hostname and ports
         return protected_uri_with_hostname if internal?(uri)
 

spec/lib/gitlab/url_blocker_spec.rb

@@ -91,6 +91,21 @@ RSpec.describe Gitlab::UrlBlocker, :stub_invalid_dns_only do
       end
     end
 
+    context 'DNS rebinding protection with IP allowed' do
+      let(:import_url) { 'http://a.192.168.0.120.3times.127.0.0.1.1time.repeat.rebind.network:9121/scrape?target=unix:///var/opt/gitlab/redis/redis.socket&check-keys=*' }
+
+      before do
+        stub_dns(import_url, ip_address: '192.168.0.120')
+
+        allow(Gitlab::UrlBlockers::UrlAllowlist).to receive(:ip_allowed?).and_return(true)
+      end
+
+      it_behaves_like 'validates URI and hostname' do
+        let(:expected_uri) { 'http://192.168.0.120:9121/scrape?target=unix:///var/opt/gitlab/redis/redis.socket&check-keys=*' }
+        let(:expected_hostname) { 'a.192.168.0.120.3times.127.0.0.1.1time.repeat.rebind.network' }
+      end
+    end
+
     context 'disabled DNS rebinding protection' do
       subject { described_class.validate!(import_url, dns_rebind_protection: false) }