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Critical · 9.1 Public exploit CVE-2026-56111 EUVD-2026-38797GHSA-x5qg-qgv8-q7cr

Marlin Firmware 2.1.2.7 Out-of-Bounds Write via M421 G-code Handler

Published Jun 24, 2026 · Updated Nov 8, 2026 · Assigned by VulnCheck

Vendor: MarlinFirmware Product: Marlin

Description

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

VendorProductAffectedFixed
MarlinFirmware Marlin ≤ 2.1.2.7 —

Public exploits

Exploit or proof-of-concept code for this vulnerability is publicly available, which lowers the bar for attackers. Treat it as a reason to patch sooner.

Third-party code, not reviewed by us. Public PoCs are sometimes fake or contain malware. Read the code first and run it only in an isolated lab, against systems you are authorised to test.

GitHub 1 repository

  • Christbowel/CVE-2026-56111 ★ 1 · Jun 24, 2026

    Proof of concept for CVE-2026-56111, an out-of-bounds write in the M421 G-code handler of Marlin Firmware

Sources: PoC-in-GitHub, Metasploit Framework, Exploit-DB — updated daily. Only links are listed; no exploit code is hosted here.

References