Merge #2709

2709: Validate proxy ip with PROXY_AUTH_WHITELIST r=mergify[bot] a=Diman0

## What type of PR?

bug fix

## What does this PR do?
The Proxy code validated the real client ip against the proxy auth whitelist. It should be the proxy ip that is checked. That is changed with this PR.

### Related issue(s)
- closes #2708
- #2692

## Prerequisites
Before we can consider review and merge, please make sure the following list is done and checked.
If an entry in not applicable, you can check it or remove it from the list.

- [n/a] In case of feature or enhancement: documentation updated accordingly
- [x] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/workflow.html#changelog) entry file.


Co-authored-by: Dimitri Huisman <diman@huisman.xyz>

core/admin/mailu/sso/views/base.py

@@ -78,8 +78,8 @@ def logout():
 Redirect to the url passed in parameter if any; Ensure that this is not an open-redirect too...
 https://cheatsheetseries.owasp.org/cheatsheets/Unvalidated_Redirects_and_Forwards_Cheat_Sheet.html
 """
-def _has_usable_redirect():
+def _has_usable_redirect(is_proxied=False):
-    if 'homepage' in flask.request.url:
+    if 'homepage' in flask.request.url and not is_proxied:
         return None
     if url := flask.request.args.get('url'):
         url = url_unquote(url)
@@ -92,15 +92,16 @@ def _has_usable_redirect():
 https://mailu.io/master/configuration.html#header-authentication-using-an-external-proxy
 """
 def _proxy():
-    ip = ipaddress.ip_address(flask.request.remote_addr)
+    proxy_ip = flask.request.headers.get('X-Forwarded-By', flask.request.remote_addr)
+    ip = ipaddress.ip_address(proxy_ip)
     if not any(ip in cidr for cidr in app.config['PROXY_AUTH_WHITELIST']):
-        return flask.abort(500, '%s is not on PROXY_AUTH_WHITELIST' % flask.request.remote_addr)
+        return flask.abort(500, '%s is not on PROXY_AUTH_WHITELIST' % proxy_ip)
 
     email = flask.request.headers.get(app.config['PROXY_AUTH_HEADER'])
     if not email:
         return flask.abort(500, 'No %s header' % app.config['PROXY_AUTH_HEADER'])
 
-    url = _has_usable_redirect() or app.config['WEB_ADMIN']
+    url = _has_usable_redirect(True) or app.config['WEB_ADMIN']
 
     user = models.User.get(email)
     if user:

core/nginx/conf/nginx.conf

@@ -231,6 +231,7 @@ http {
         auth_request /internal/auth/admin;
         proxy_set_header X-Real-IP "";
         proxy_set_header X-Forwarded-For "";
+        proxy_set_header X-Forwarded-By: "";
         proxy_pass http://$antispam;
         error_page 403 @sso_login;
       }

core/nginx/conf/proxy.conf

@@ -7,8 +7,10 @@ proxy_hide_header CF-Connecting-IP;
 proxy_set_header X-Forwarded-Proto $proxy_x_forwarded_proto;
 {% if REAL_IP_HEADER and REAL_IP_FROM %}
 proxy_set_header X-Forwarded-For $proxy_add_x_forwarded_for;
+proxy_set_header X-Forwarded-By $realip_remote_addr;
 {% else %}
 proxy_set_header X-Forwarded-For $remote_addr;
+proxy_hide_header X-Forwarded-By;
 {% endif %}
 proxy_http_version 1.1;
 proxy_hide_header Forwarded;

towncrier/newsfragments/2708.bugfix

@@ -0,0 +1,3 @@
+Proxy authentication was using the real client ip instead of the proxy
+IP for checking the PROXY_AUTH_WHITELIST.
+