gitlab behind caddy proxy shows invalid IP in case of failed signin

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Summary

We are running gitlab in docker behind caddy as reverse-proxy. When login failes, gitlab sends a notification about the inncorrect verification code. In this email is the IP Address of docker network and not the ip address of real origin.

Steps to reproduce

  1. setup caddy as reverse proxy (may not be necessary)
  2. Setup gitlab in docker with outgoing mail
  3. Add a gitlab user & mail address with two factor (authenticator)
  4. Login with this user, but enter invalid authenticator code

Example Project

N/A

What is the current bug behavior?

IP Address of network inside docker is part of notification mail

What is the expected correct behavior?

IP adress of real origin

Relevant logs and/or screenshots

unfortunately only available in german..

GitLab hat den Versuch einer Anmeldung mit einem falschen Bestätigungscode an deinem git.datenzentrale.online-Konto entdeckt. 

  
Hostname 	git.xxxxxxx.online 
IP-Adresse 	172.20.0.1 
Zeit 	2025-09-30 12:40:24 UTC

Output of checks

Results of GitLab environment info

Expand for output related to GitLab environment info 

(For installations with omnibus-gitlab package run and paste the output of:
`sudo gitlab-rake gitlab:env:info`)
System information
System:
Proxy:          no
Current User:   git
Using RVM:      no
Ruby Version:   3.2.8
Gem Version:    3.7.1
Bundler Version:2.7.1
Rake Version:   13.0.6
Redis Version:  7.2.10
Sidekiq Version:7.3.9
Go Version:     unknown

GitLab information
Version:        18.4.0-ee
Revision:       9255f56b458
Directory:      /opt/gitlab/embedded/service/gitlab-rails
DB Adapter:     PostgreSQL
DB Version:     16.8
URL:            https://git.datenzentrale.online
HTTP Clone URL: https://git.datenzentrale.online/some-group/some-project.git
SSH Clone URL:  ssh://git@git.datenzentrale.online:55522/some-group/some-project.git
Elasticsearch:  no
Geo:            no
Using LDAP:     no
Using Omniauth: yes
Omniauth Providers:

GitLab Shell
Version:        14.45.2
Repository storages:
- default:      unix:/var/opt/gitlab/gitaly/gitaly.socket
GitLab Shell path:              /opt/gitlab/embedded/service/gitlab-shell

Gitaly
- default Address:      unix:/var/opt/gitlab/gitaly/gitaly.socket
- default Version:      18.4.0
- default Git Version:  2.50.1
(For installations from source run and paste the output of:
`sudo -u git -H bundle exec rake gitlab:env:info RAILS_ENV=production`)

Results of GitLab application Check

Expand for output related to the GitLab application check 
(For installations with omnibus-gitlab package run and paste the output of:
sudo gitlab-rake gitlab:check SANITIZE=true)


(For installations from source run and paste the output of:
sudo -u git -H bundle exec rake gitlab:check RAILS_ENV=production SANITIZE=true)


(we will only investigate if the tests are passing)

Possible fixes

Patch release information for backports

If the bug fix needs to be backported in a patch release to a version under the maintenance policy, please follow the steps on the patch release runbook for GitLab engineers.

Refer to the internal "Release Information" dashboard for information about the next patch release, including the targeted versions, expected release date, and current status.

High-severity bug remediation

To remediate high-severity issues requiring an internal release for single-tenant SaaS instances, refer to the internal release process for engineers.

Edited by 🤖 GitLab Bot 🤖