Project Zomboid 42.21 and 42.22: what changes for servers

A lot has happened in Project Zomboid: Build 42.21 has been the Stable version since September 28, 2026. On October 27, The Indie Stone released Build 42.22 "Moving on Up" on a new Pre-Release branch, which has since received two hotfixes. For server admins, 42.21 is the one that matters most, because it closes a security hole. 42.22 is a preview of the next Stable update.

Build 42.21 (Stable)

Security hole closed. 42.21 fixes a Steam authentication exploit. It let players join dedicated servers without correctly authenticating via Steam, which also got around SteamID bans. If you run a public server and keep people out with bans, do not skip this update.

Also in 42.21:

• The worst cases of zombie duplication in multiplayer are fixed. According to The Indie Stone, a few cases remain and should be fixed in the next update.
• Zombies disappear less often after you leave and re-enter a chunk, in single player and multiplayer.
• The server browser now shows the last wipe under Server Update instead of the last restart.
• Players get a notification when they try to connect to a server running a different game version.
• Anti-cheat now guards against more cheats, and safehouse exploits are fixed.
• Less juddering when driving at high ping (around 150 ms and up) and a fixed desync between floor levels.
• XXL trees cut away better while driving and no longer hide houses and furniture.
• The Lua methods loadstring and loadstream are back. They had been removed in the 42.20.4 security hotfix on August 26.

There are balance changes too, for example explosives now work in basements. According to the patch notes, existing 42.20.4 saves should keep working. The Indie Stone still recommends a backup. You can find the full list in the 42.21 patch notes on the Indie Stone forums.

Build 42.22 (Pre-Release)

The Pre-Release branch replaces the old Unstable branch. New builds will land there first and stay for at least one week before they move to Stable. Only urgent hotfixes may go straight to Stable. The Indie Stone explicitly aims the branch at modders, multiplayer server admins and anyone who likes testing. For regular players, the studio still recommends Stable 42.21, so servers on the default branch keep running 42.21.

What 42.22 brings:

• Ladders: Placed ladders on the map can be used with the E key.
• Crowbars: Through the right-click menu you can force open locked windows, doors, garage doors and gates. Security and jail cell doors stay shut. Burglars are handier and quieter at it, strength helps, and failing often makes damage to the crowbar more likely.
• Smaller changes: You can push while carrying encumbering items and open ammo boxes while walking. Characters can no longer sleep while the Bad Smell moodle is present.
• Animals: Animals no longer die when their cell unloads, and chickens no longer disappear from full hutches.
• For servers: faster server backups, no more duplicate characters, PvP damage is calculated on the server, trailer fixes, and the "All Known on Start" sandbox option works again. Notes on map items save again, and anti-cheat measures were updated.

Hotfix 42.22.1 (November 4) fixes a certificate validation vulnerability and adds integrity checks for the Java runtime. The game shows detected modifications in the version watermark. Hotfix 42.22.2 (November 6) fixes this check showing incorrectly on Windows. According to The Indie Stone, neither hotfix should break saves. All details are in the 42.22 patch notes.

What this means for your server

Server and players have to run the same version. If your server is on 42.21 Stable, every player has to stay on the default branch as well. Anyone who switches to Pre-Release can no longer join your server, but thanks to 42.21 they at least get a notice about the version mismatch.

Mods deserve a close look. Lua mods from the Steam Workshop are the officially supported route. Mods that need loadstring or loadstream can use those methods again since 42.21. Test Java mods and custom loaders individually after every update.

Do not plan on a way back: The Indie Stone explicitly warns that a save from the Pre-Release branch may not work in the final release.

What to do now

1. Take a backup
   Back up your save before you update.

2. Update to 42.21
   Bring your server to 42.21 Stable and restart it. That closes the Steam authentication hole, and your bans hold reliably again.

3. Check your mods
   Compare your mod list with the patch notes and test Java mods before going live.

4. Tell your players
   Let your community know they should stay on the Stable branch as long as your server runs there.

5. Use Pre-Release only for testing
   If you want to try 42.22, use a copy of your save or a separate test server. Your players then have to use the Pre-Release branch as well.

Looking for a server for Knox County? You can get your Project Zomboid server with us.