CVE-2026-63995 ethtool: cmis: validate start_cmd_payload_size from module

High 7.8 Published 19 Jul 2026 Updated 19 Oct 2026

A malicious network module can trigger an out-of-bounds write in the Linux kernel CMIS firmware update code, potentially leading to code execution or privilege escalation.

Exploited in the wild: Not known
Login needed: Any signed-in user
Attackable: Local or same network only
Victim action needed: Not needed
Fix: Available

What is CVE-2026-63995?

CVE-2026-63995 is a high-severity memory corruption vulnerability in Linux kernel, published on 19 Jul 2026. It can only be exploited from the same machine or local network, with no action from the victim.

Official description

In the Linux kernel, the following vulnerability has been resolved:

ethtool: cmis: validate start_cmd_payload_size from module

The CMIS firmware update code reads start_cmd_payload_size from the module's FW Management Features CDB reply and uses it directly as the byte count for memcpy. The destination buffer is 112 bytes (ETHTOOL_CMIS_CDB_LPL_MAX_PL_LENGTH - 8). So a malicious module (or corrupted response) can cause a OOB write later on in cmis_fw_update_start_download().

Let's error out. If modules that expect longer LPL writes actually exist we should revisit.

struct cmis_cdb_start_fw_download_pl's definition has to move, no change there.

Weakness: CWE-787

Which versions are affected by CVE-2026-63995?

It affects 1 product.

Products include Linux kernel.

How do I fix CVE-2026-63995?

Apply the vendor's patch.

Upgrade to the fixed version. Memory-safe languages, compiler hardening and fuzzing prevent most new cases. More about Memory corruption.

Is CVE-2026-63995 being exploited?

There is no known exploitation of CVE-2026-63995 in the wild and no public exploit code.

All Linux kernel vulnerabilities

Sources

Also known as BELL-CVE-2026-63995, DEBIAN-CVE-2026-63995, GHSA-g8c6-c8ph-pp93, UBUNTU-CVE-2026-63995.