Use-after-free in Linux kernel - CVE-2026-63918

Vulnerability identifier: #VU138738

CSH Severity: Low

CVSS v4: 5.7 [CVSS:4.0/AV:L/AC:L/AT:P/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-63918

CWE-ID: CWE-416

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a local user to cause a use-after-free.

The vulnerability exists due to a use-after-free in l2tp_session_get_by_ifname() in the l2tp core when looking up a session by interface name during an RCU-protected list walk. A local user can trigger a race condition that returns a session pointer after its reference count has reached zero to cause a use-after-free.

On PREEMPT_RT kernels, the preemption window is real between the interface name comparison and reference count increment.

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/05f95729ca844704d15e49ce14868af4b403b32b
• https://git.kernel.org/stable/c/782d60a6596aee9b29c2eecfa70033899278bf65
• https://git.kernel.org/stable/c/947013fd7c8c35dd5856557b215840098a3f67f8
• https://git.kernel.org/stable/c/ee80455feffb9cb62b5b58715cabeff495e666b2

• Use-after-free in Linux kernel l2tp
• 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