SB20260720248 - Stack-based buffer overflow in Linux kernel sched

Description

This security bulletin contains information about 1 vulnerability.

1) Stack-based buffer overflow (CVE-ID: CVE-2026-63981)

CWE-ID: CWE-121 - Stack-based buffer overflow

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.

The vulnerability exists due to a stack overflow in tcf_mirred_act() when processing mirred blockcast actions on shared TC egress blocks. A local user can create dummy devices, attach clsact qdiscs with shared blocks, and install mirred blockcast filters to cause a denial of service.

Exploitation is reachable via user and network namespaces created with unshare(CLONE_NEWUSER | CLONE_NEWNET), which grants CAP_NET_ADMIN in the new network namespace.

Remediation

Install update from vendor's website.

References

• https://git.kernel.org/stable/c/25fc9352590f5ef21ebf290432bd768b336693bc
• https://git.kernel.org/stable/c/34457de389fb64a01fdcc71177dfebe65fd2d362
• https://git.kernel.org/stable/c/a005fa5d7502eefec7ee6e1c01adadc06de2f9ad