Project Zomboid’s 3 Hotfixes Address Security Issues Across Stable, Unstable, and Legacy Builds
The changes also remove the loadstring and loadstream methods, so affected mods will need updates.
Project Zomboid has three branch hotfixes available as of August 26, 2026: 42.20.4 for stable, 42.19.2 for unstable, and 41.78.21 for legacy. The main change addresses security vulnerabilities, while mod authors will need to account for the removal of two methods.
The Indie Stone detailed the release in its Steam announcement. The team said the hotfixes should not break existing saves. If a bug appears, players should reproduce it on a fresh save without mods before sending a report through the official bug reports forum.
Mod creators face the biggest change. The loadstring and loadstream methods have been removed, so mods that depended on them will need to be updated. Mods that used those methods to execute code sent by a server will need replacement methods and updated command handling.
The stable release follows Project Zomboid’s 42.20.3 hotfix, which addressed multiplayer hangs, memory leaks, and other technical problems. Players on the stable branch should now see 42.20.4 instead.
Project Zomboid 42.20.4, 42.19.2, and 41.78.21 Patch Notes
All three versions share the security fix. For players, save compatibility remains the main reassurance; for mod makers, the removed methods are the key technical change.
- Fixed security vulnerabilities.
- Mod makers should be aware that as part of this fix, the loadstring and loadstream methods have been removed. If your mods used these methods you will need to update your mods. If you were using these methods to execute code sent from the server, then you will need to create the necessary methods and call them by sending the appropriate commands. If you are unable to replace these methods in your case, please report the issue in the #mod_portal channel of The Official Project Zomboid Discord server, explaining how you were using them
The three hotfixes keep the stable, unstable, and legacy branches moving on separate version tracks while giving mod authors a clear compatibility task. Share your thoughts in the comments, and follow us on X, Bluesky, YouTube, Instagram, Steam, Telegram.
