SB20260720323 - Use-after-free in Linux kernel l2tp

Description

This security bulletin contains information about 1 vulnerability.

1) Use-after-free (CVE-ID: CVE-2026-63918)

CWE-ID: CWE-416 - Use After Free

CVSSv4: 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]

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.

Remediation

Install update from vendor's website.

References

• 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