Out-of-bounds write in Linux kernel - CVE-2026-63995

Vulnerability identifier: #VU138647

CSH Severity: Medium

CVSS v4: 5.1 [CVSS:4.0/AV:P/AC:L/AT:N/PR:N/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-63995

CWE-ID: CWE-787

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows an attacker with physical access to cause memory corruption.

The vulnerability exists due to an out-of-bounds write in cmis_fw_update_start_download() when processing a CMIS module firmware management features reply. An attacker with physical access can provide a malicious module response with an oversized start command payload value to cause memory corruption.

A malicious module or a corrupted response can trigger the issue during CMIS firmware update handling.

Linux kernel
Ubuntu
linux-ibm (Ubuntu package)
linux-azure (Ubuntu package)
linux-aws (Ubuntu package)
linux-nvidia (Ubuntu package)
linux-nvidia-bos (Ubuntu package)

Install security update from vendor's repository.

Linux kernel - update to 7.0 rc3
linux-ibm (Ubuntu package) - addressed in versions 7.0.0-1008.8, 7.0.0-1010.10
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1010.10
linux-aws (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1015.15
linux-nvidia (Ubuntu package) - addressed in versions 7.0.0-1016.16, 7.0.0-1016.16~24.04.1
linux-nvidia-bos (Ubuntu package) - update to 7.0.0-2016.16

• https://git.kernel.org/stable/c/0696709e951be54c699664adf546d16e28974d53
• https://git.kernel.org/stable/c/12c2496a71f82f63617971ca9b730dffa05cf58b
• https://git.kernel.org/stable/c/63112b4515469d00008452d9cfe3fb3bf1aa2df3
• https://git.kernel.org/stable/c/a46340da00385be7fb16c62425ebc20006f2d5d8

• Out-of-bounds write in Linux kernel ethtool
• Ubuntu update for linux-ibm
• Ubuntu update for linux-azure
• Ubuntu update for linux-aws
• Ubuntu update for linux-nvidia-bos
• Ubuntu update for linux-nvidia