Improper access control in Linux kernel - CVE-2026-63921

Vulnerability identifier: #VU138726

CSH Severity: Low

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

CVE-ID: CVE-2026-63921

CWE-ID: CWE-284

Exploitation vector: Local access

Exploit availability: No public exploit available

The vulnerability allows a local user to redirect packets across network namespaces.

The vulnerability exists due to improper access control in vti6_siocdevprivate() in the IPv6 VTI tunnel handling code when processing SIOCCHGTUNNEL requests on a migrated tunnel. A local user can supply tunnel parameters that collide with a tunnel in the creation namespace to redirect packets across network namespaces.

Exploitation is reachable from an unprivileged user namespace and can have cross-tenant scope on container hosts.

Linux kernel
openEuler
Ubuntu
kernel
kernel-tools-debuginfo
kernel-tools
kernel-source
kernel-headers
kernel-devel
kernel-debugsource
kernel-debuginfo
bpftool-debuginfo
bpftool
kernel-tools-devel
perf
perf-debuginfo
python3-perf
python3-perf-debuginfo
kernel-extra-modules
linux-ibm (Ubuntu package)
linux-aws (Ubuntu package)
linux-azure (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
kernel - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
kernel-tools-debuginfo - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
kernel-tools - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
kernel-source - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
kernel-headers - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
kernel-devel - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
kernel-debugsource - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
kernel-debuginfo - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
bpftool-debuginfo - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
bpftool - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
kernel-tools-devel - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
perf - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
perf-debuginfo - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
python3-perf - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
python3-perf-debuginfo - addressed in versions 5.10.0-330.0.0.231, 6.6.0-145.3.29.160
kernel-extra-modules - update to 6.6.0-145.3.29.160
linux-ibm (Ubuntu package) - addressed in versions 7.0.0-1008.8, 7.0.0-1010.10
linux-aws (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1015.15
linux-azure (Ubuntu package) - addressed in versions 7.0.0-1009.9, 7.0.0-1010.10
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/1acfb7d9c6fc7e209ed7789392697e97e03edd33
• https://git.kernel.org/stable/c/44d2ff7d2178503b93151140a45dfa2ad49c9906
• https://git.kernel.org/stable/c/596f6354c96a891e58c04a09cbfb7b0d1ec00dab
• https://git.kernel.org/stable/c/853f6ea482dfcd3404bbef458ab4d68364eed838
• https://git.kernel.org/stable/c/8b484efd5cb4eeef9021a661e198edc5349dacf6
• https://git.kernel.org/stable/c/94ff740a7f9ef5c010784a325dca00cbf228f941
• https://git.kernel.org/stable/c/d2236348414bdd6558385f35aa7fdc9bf5634011
• https://git.kernel.org/stable/c/df42ac708acc3399bbb6dc5ca16e0540adda7bbf

• Improper access control in Linux kernel ipv6
• 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
• openEuler 22.03 LTS SP4 update for kernel
• openEuler 24.03 LTS SP3 update for kernel