Improper locking in Linux kernel - CVE-2026-63980

Vulnerability identifier: #VU138664

CSH Severity: Low

CVSS v4: 6.8 [CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:N/VI:N/VA:H/SC:N/SI:N/SA:N]

CVE-ID: CVE-2026-63980

CWE-ID: CWE-667

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a local user to cause a denial of service.

The vulnerability exists due to improper lock handling in the net/handshake subsystem when canceling a TLS handshake from softirq context while the same lock is held in process context on the same CPU. A local user can trigger a TLS handshake cancellation race to cause a denial of service.

The issue results in a deadlock.

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/06ab5978866fc2221b910347fd3e510ca8e7b1a4
• https://git.kernel.org/stable/c/0866569fc36a56f568acd3900d354e3505932e09
• https://git.kernel.org/stable/c/91898de9501a047ba67c6b864dcd403e00bdfbf5
• https://git.kernel.org/stable/c/cc993e0927ec8bd98ea33377ada03295fcda0f24

• Improper locking in Linux kernel handshake
• 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