Stack-based buffer overflow in Linux kernel - CVE-2026-63981
Published: July 20, 2026
Vulnerability identifier: #VU138665
CSH Severity: Low
CVSS v4.0: 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/E:U/U:Clear
CVE-ID: CVE-2026-63981
CWE-ID: CWE-121
Exploitation vector: Local access
Exploit availability:
No public exploit available
Vendor: Linux Foundation
Affected software:
Linux kernel
Linux kernel
Detailed vulnerability description
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.
How to mitigate CVE-2026-63981
Install security update from vendor's repository.