1 files changed, 49 insertions, 0 deletions
diff --git a/config/initializers/http_hostname_override.rb b/config/initializers/http_hostname_override.rb
new file mode 100644
index 00000000000..58dd380326f
--- /dev/null
+++ b/config/initializers/http_hostname_override.rb
@@ -0,0 +1,49 @@
+# This override allows passing `@hostname_override` to the SNI protocol,
+# which is used to lookup the correct SSL certificate in the
+# request handshake process.
+#
+# Given we've forced the HTTP request to be sent to the resolved
+# IP address in a few scenarios (e.g.: `Gitlab::HTTP` through
+# `Gitlab::UrlBlocker.validate!`), we need to provide the _original_
+# hostname via SNI in order to have a clean connection setup.
+#
+# This is ultimately needed in order to avoid DNS rebinding attacks
+# through HTTP requests.
+#
+class OpenSSL::SSL::SSLContext
+  attr_accessor :hostname_override
+end
+
+class OpenSSL::SSL::SSLSocket
+  module HostnameOverride
+    # rubocop: disable Gitlab/ModuleWithInstanceVariables
+    def hostname=(hostname)
+      super(@context.hostname_override || hostname)
+    end
+
+    def post_connection_check(hostname)
+      super(@context.hostname_override || hostname)
+    end
+    # rubocop: enable Gitlab/ModuleWithInstanceVariables
+  end
+
+  prepend HostnameOverride
+end
+
+class Net::HTTP
+  attr_accessor :hostname_override
+  SSL_IVNAMES << :@hostname_override
+  SSL_ATTRIBUTES << :hostname_override
+
+  module HostnameOverride
+    def addr_port
+      return super unless hostname_override
+
+      addr = hostname_override
+      default_port = use_ssl? ? Net::HTTP.https_default_port : Net::HTTP.http_default_port
+      default_port == port ? addr : "#{addr}:#{port}"
+    end
+  end
+
+  prepend HostnameOverride
+end