IpLock

A server-side Fabric mod that prevents account takeovers on offline-mode Minecraft servers by binding each username to the IP address it first joined from.

How it works

When a player joins for the first time, their username is permanently bound to their IP address. If the same username later connects from a different IP, that IP is immediately banned and the connection is rejected. This makes it effectively impossible to impersonate an existing player from a different machine.

• First join — username is bound to the connecting IP, player joins normally.
• Same IP — player joins normally.
• Different IP — connection is rejected and the new IP is banned.

Data is stored in iplock/bindings.json and iplock/bans.json inside the server's run directory.

Commands

All commands require operator level 3 (admin).

Command	Description
/iplock list	Show all username → IP bindings
/iplock bans	Show all banned IPs and which username they tried to use
/iplock unban <ip>	Remove an IP from the ban list
/iplock reset <username>	Delete a username's IP binding (allows them to re-bind from a new IP)