Cloudanix VulnDB

CVE-2026-99250

None

CVSS

—

EPSS

0.2%

Published

Nov 3, 2026

CISA due date

—

Cloudanix analysis

Schedule a fix SSVC: Track

A Linux kernel startup timing problem can cause some multi-processor computers to freeze before they finish booting.

Exploitation
Other
Attacker needs
None
Complexity
Theoretical
Impact
Denial Of Service
Component
OS kernel
Class
Race Condition
Remediation
Patch
Effort
Medium
Patch risk
Low

What it actually does

NBCON console kthreads are started via early_initcall() and asynchronously toggle interrupts, racing with SMP initialization and causing missed IPIs that hang the system on certain hardware.

Why it matters to the business

Affected Linux systems may hang during boot on SMP platforms, producing unpredictable startup failures and requiring manual intervention or console disabling to restore service.

How an attack unfolds

No attacker action is required; the race occurs automatically during early kernel boot when NBCON kthreads enable or disable interrupts before architecture-specific SMP setup completes on vulnerable hardware.

How to fix it

Apply the upstream fix that moves NBCON kthread creation after all architecture initcalls complete; rebuild and deploy the patched kernel.

How to confirm the fix worked

Confirm the change by inspecting printk initcall ordering in the patched source and verify that systems previously exhibiting the hang now boot cleanly with NBCON enabled.

Typical attack path

  1. Boot kernel on SMP hardware that triggers the race
  2. early_initcall starts NBCON kthreads
  3. kthreads asynchronously change interrupt state
  4. SMP setup misses required IPIs and hangs

How to detect it

Review early boot logs for repeated SMP IPI timeout messages or hangs that resolve when NBCON console support is disabled; no post-boot artifacts are produced.

What your security team should do

  • Prioritize patching kernels on SMP servers within the next maintenance window
  • Monitor boot logs on all Linux systems for unexplained early SMP hangs
  • Temporarily disable NBCON consoles only if reboot reliability cannot be restored by patching

The record

In the Linux kernel, the following vulnerability has been resolved: printk: Postpone kthread startup There have been various bug reports related to SMP systems hanging on boot. The reports vary but seem to have some overlap with regard to missed IPI's during SMP setup. The reports also show that reverting NBCON console usage allows the bugs to disappear. The NBCON kthreads for console printing are started very early during boot using early_initcall(). Since these kthreads are asynchronously enabling/disabling interrupts during early boot, they may be interfering with early SMP setup on some hardware platforms. Starting the console printing kthreads later has shown to avoid the hanging on systems that could previously reproduce the issue. Postpone kthread starting until after all arch initcalls have completed.

Affected packages

Ecosystem Package Introduced Fixed