https://github.com/bitcoin/bitcoin/blob/d72758c3f6c34cd835f5de3efc230964f3b1ea56/src/torcontrol.cpp#L539

If a user is running Tor proxy outside localhost (perhaps on other host inside LAN or in containerised environment) , the automatic creation of onion services ends up creating an onion service listening to hardcored 127.0.0.1 address on the Tor proxy's host instead of the private address of the bitcoind – effectively running an empty onion service listening the Tor proxy's localhost.
#include <util/threadnames.h>
#include <util/translation.h>
#include <validation.h>
#include <validationinterface.h>
#include <walletinitinterface.h>
#include <functional>
#include <set>
#include <stdint.h>
#include <stdio.h>
#ifndef WIN32
#include <attributes.h>
#include <cerrno>
#include <signal.h>
#include <sys/stat.h>
#endif
#include <boost/algorithm/string/replace.hpp>
#include <boost/signals2/signal.hpp>
#include <boost/thread/thread.hpp>
#if ENABLE_ZMQ
#include <zmq/zmqabstractnotifier.h>
#include <zmq/zmqnotificationinterface.h>
#include <zmq/zmqrpc.h>
#endif
static bool fFeeEstimatesInitialized = false;
static const bool DEFAULT_PROXYRANDOMIZE = true;
static const bool DEFAULT_REST_ENABLE = false;
static const bool DEFAULT_STOPAFTERBLOCKIMPORT = false;
#ifdef WIN32
#define MIN_CORE_FILEDESCRIPTORS 0
#else