Security Issue: Bug in shift72/caddy-geo-ip causes RemoteAddr to be overwritten for the whole request

Not sure where or if this is appropriate to post, but I felt the need to notify people of this bug as it has security implications for those who use this plugin. The plugin has a fair amount of downloads on

I’ve opened an issue Security: trust_header overwrites req.RemoteAddr globally · Issue #4 · shift72/caddy-geo-ip · GitHub, however I feel like users of the plugin are more likely to see it here.

when the trust_header directive is set in caddy-geo-ip, it overwrites req.RemoteAddr to the value of the header. This then gets passed down to other plugins and directives which share the same request. {
geo_ip {
        db_path /var/lib/GeoIP/GeoLite2-City.mmdb
        trust_header X-Forwarded-For

respond /test 200 {
        body "Remote Address:{remote_host}"

With the above config curl -H "X-Forwarded-For:" would respond with Remote Address: showing that the value was changed outside of the geoip scope

This could allow people to bypass IP range restrictions and perhaps many other things I haven’t thought of.

1 Like

Thanks for bringing that up.

FYI, Caddy will soon have an official and secure way to determine the client IP:

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