CVE-2026-56111: Marlinfirmware Marlin

Critical severity, CVSS 9.1. EPSS: 0.6% chance of exploitation in the next 30 days.

Marlin Firmware through 2.1.2.7, fixed in commit 1f255d1, when built with MESH_BED_LEVELING enabled, contains an out-of-bounds write vulnerability in the M421 G-code handler that allows attackers to corrupt firmware memory by supplying out-of-range X and Y grid indices. Attackers can send a single crafted G-code command via USB serial, network interface, or malicious gcode file to write an attacker-controlled 32-bit float value past the z_values array bounds, corrupting adjacent firmware variables and causing denial of service or firmware state corruption.

Affected products

• Marlinfirmware Marlin: up to and including 2.1.2.7

Published 2026-06-24. Last modified 2026-07-14.