SB20261023169 - Use-after-free in Linux kernel fs

Description

This security bulletin contains information about 1 vulnerability.

1) Use-after-free (CVE-ID: CVE-2026-98991)

CWE-ID: CWE-416 - Use After Free

CVSSv4: 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]

The vulnerability allows a local user to cause a denial of service through a kernel use-after-free.

The vulnerability exists due to use-after-free in the Linux kernel mount notification mechanism when repeated unmount operations queue the same mount more than once during a single namespace_sem hold. A local user can trigger these operations in a mount namespace with a FAN_MARK_MNTNS mark to corrupt the notification list, causing subsequent host mount operations to access freed memory and potentially crash the kernel.

Exploitation requires a mount with MNT_SHRINKABLE to bind from.

Remediation

Install update from vendor's website.

References

• https://git.kernel.org/stable/c/702ff3fe499876e09c45558a05366d21a5bc41ab
• https://git.kernel.org/stable/c/acbe9e4418e2ef7bef1a12e62e0e7d6145a15190
• https://git.kernel.org/stable/c/bd2feb7796b6585938a4241e7b7c4148a6f7b762