Vulnerability · Published Jun 24, 2026 · Assigned by VulnCheck
CVE-2026-56111Marlin Firmware 2.1.2.7 Out-of-Bounds Write via M421 G-code Handler
Critical 9.1
In plain English
A critical-severity security flaw in Marlin from MarlinFirmware. Proof-of-concept exploit code is public. The chance it is exploited in the next 30 days is estimated at 0.6% (higher than 51% of all known vulnerabilities). Ready-made attack tooling exists: public proof-of-concept code.
Official 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 (as reported)
| Vendor | Product | Versions |
|---|---|---|
| MarlinFirmware | Marlin | 0 – through 2.1.2.7 |
Weakness: CWE-129 · Vector: CVSS:3.1/AV:N/AC:L/PR:N/UI:N/S:U/C:N/I:H/A:H
References
- Researcher Disclosure technical-description, exploit
- Pull Request issue-tracking
- Patch Commit patch
- https://www.vulncheck.com/advisories/marlin-firmware-out-of-bounds-write-via-m421-g-code-handler third-party-advisory