Prusa error 13606 (Signature Verification Failed) appears on the MK4 and its equivalents are #31606 on the CORE One, #35606 on the CORE One L, #26606 on the MK4S, #27606 on the MK3.9S, #21606 on the MK3.9, #28606 on the MK3.5S, and #23606 on the MK3.5. The printer attempted to install a firmware file that does not carry a valid cryptographic signature from Prusa Research, and blocked the update.

What the Error Means

MK4-family printers include a firmware signing lock — the xBuddy board verifies a cryptographic signature on every firmware file before allowing it to be installed. Official Prusa firmware files are signed during the build process. If the signature is missing (as with community-built firmware) or invalid (corrupted download, wrong-model firmware file, or tampered file), the verification fails and the update is blocked. This is a deliberate security measure to prevent accidental installation of incompatible or malicious firmware. Users who want to run custom or community firmware must deliberately break the hardware signing appendix — a permanent, one-way action that voids the electronics warranty.

Step-by-Step Fix

1. Download firmware only from the official Prusa website. Go to prusa3d.com/drivers and download firmware for your exact printer model. Never download firmware from third-party sites, GitHub mirrors, or forum posts.
2. Confirm the firmware file is for your exact printer model. MK4 firmware will not pass MK4S signature verification and vice versa. Check your model number on the printer’s LCD under Settings → Info or on the printer’s nameplate.
3. Re-download the firmware if there is any doubt about file integrity. A partial or interrupted download can corrupt the signature bytes at the end of the file. Delete the file and download it fresh.
4. If you intentionally want to run custom firmware, follow the official Prusa guide. Breaking the hardware signing appendix on the xBuddy board permanently removes the signing restriction but also permanently voids the electronics warranty and cannot be undone. Only proceed if you fully understand the implications.

Parts Required

• No replacement parts are required for this fix — this is a firmware file issue

If you downloaded official firmware and are still getting this error, contact Prusa Support at help.prusa3d.com with your printer model number and the firmware file name you downloaded.

Frequently asked questions

What does Prusa 13606 mean?

Prusa error 13606 (Signature Verification Failed) appears on the MK4 and its equivalents are #31606 on the CORE One, #35606 on the CORE One L, #26606 on the MK4S, #27606 on the MK3.9S, #21606 on the MK3.9, #28606 on the MK3.5S, and #23606 on the MK3.5. The printer attempted to install a firmware file that does not carry a valid cryptographic signature from Prusa Research, and blocked the update.

How do I fix Prusa 13606?

Prusa error 13606 means the firmware file lacks a valid Prusa signature. Learn how to obtain official firmware and understand the signing lock on MK4-series printers.