CVE-2026-43271: Linux Kernel

Medium severity, CVSS 5.5. EPSS: 0.1% chance of exploitation in the next 30 days.

In the Linux kernel, the following vulnerability has been resolved: md-cluster: fix NULL pointer dereference in process_metadata_update The function process_metadata_update() blindly dereferences the 'thread' pointer (acquired via rcu_dereference_protected) within the wait_event() macro. While the code comment states "daemon thread must exist", there is a valid race condition window during the MD array startup sequence (md_run): 1. bitmap_load() is called, which invokes md_cluster_ops->join(). 2. join() starts the "cluster_recv" thread (recv_daemon). 3. At this point, recv_daemon is active and processing messages. 4. However, mddev->thread (the main MD thread) is not initialized until later in md_run(). If a METADATA_UPDATED message is received from a remote node during this specific window, process_metadata_update() will be called while mddev->thread is still NULL, leading to a kernel panic. To fix this, we must validate the 'thread' pointer. If it is NULL, we release the held lock (no_new_dev_lockres) and return early, safely ignoring the update request as the array is not yet fully ready to process it.

Affected products

• Linux Linux Kernel: from 4.12, before 6.6.128 (fixed in 6.6.128); from 6.7, before 6.12.75 (fixed in 6.12.75); from 6.13, before 6.18.16 (fixed in 6.18.16); from 6.19, before 6.19.6 (fixed in 6.19.6)

Published 2026-05-06. Last modified 2026-06-17.