CVE-2025-71119: 
Linux Kernel vulnerability analysis and mitigation

CVE-2025-71119 is a Linux kernel vulnerability in the PowerPC kexec subsystem where SMT (Simultaneous Multi-Threading) is not properly enabled before attempting to wake offline CPUs during kernel reboots. When SMT is disabled or in a partial state, the add_cpu() function fails because cpu_bootable() returns false for CPUs failing cpu_smt_thread_allowed() checks, resulting in kernel warnings and boot failures. Affected kernel versions include 6.1.72–6.1.159, 6.5.12–6.5.x, 6.6.1–6.6.119, 6.7–6.12.63, 6.13–6.18.2, and 6.19-rc1 through rc8. It was published on January 14, 2026, with patches released through the Linux kernel project. The CVSS v3.1 base score is 5.5 (Medium) (Feedly, MSRC).

The root cause is improper SMT state management in the PowerPC kexec code path (arch/powerpc/kexec/core_64.c), classified as NVD-CWE-noinfo (Insufficient Information) by NIST. When a new kernel image is loaded for kexec and SMT is disabled or partially enabled, kexec_prepare_cpus() attempts to wake all present CPUs without first re-enabling SMT, causing add_cpu() to fail for non-primary threads or CPUs that fail the cpu_smt_thread_allowed() check. The fix enables SMT and resets the SMT thread count to the number of threads per core before the CPU wake-up sequence. This is a local, low-complexity issue requiring low privileges and no user interaction to trigger (Feedly, MSRC).

Exploitation of this vulnerability results in availability impact only — there is no confidentiality or integrity impact. On affected PowerPC systems with SMT disabled or partially enabled, initiating a kexec operation causes kernel warnings in kexec_prepare_cpus and prevents proper CPU initialization during the reboot process, leading to reboot failures and system instability. This primarily affects PowerPC servers and embedded systems relying on kexec for live kernel updates, potentially disrupting critical operations that depend on seamless kernel reboots (Feedly).

Apply the available patches from the Linux kernel project targeting the affected stable branches. Fixed versions include kernel 6.1.160, 6.6.120, 6.12.64, 6.18.3, and later. Five patch commits are available via kernel.org: 0d5c9e9, 7cccd82, c2296a1, d790ef0, and f0c0a68. As a temporary workaround for systems that cannot be immediately patched, avoid initiating kexec operations until patches are applied (Feedly, MSRC).