Cloudanix VulnDB

CVE-2026-98390

None

CVSS

—

EPSS

0.2%

Published

Oct 14, 2026

CISA due date

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Cloudanix analysis

Schedule a fix SSVC: Track

A calculation error in the Linux kernel can make certain virtual servers crash during startup when running under specific virtualization software.

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

What it actually does

Division by zero in x86/amd_node topology code when roots_per_node evaluates to zero on virtualized systems (e.g., Xen PVH dom0 where num_nodes=2 and num_roots=1), causing kernel panic.

Why it matters to the business

Unexpected system crashes and downtime on affected virtualized Linux deployments, interrupting workloads until the kernel is updated or the hypervisor configuration is adjusted.

How an attack unfolds

An attacker with control over the virtualized environment provisions or migrates a guest that triggers the Xen PVH topology mismatch, causing the divide-by-zero during node enumeration and resulting in a denial-of-service crash; no remote code execution is possible.

How to fix it

Update to a Linux kernel containing the fix that sets roots_per_node=1 when the value would otherwise be zero and logs a firmware bug warning on non-virtualized systems.

How to confirm the fix worked

Boot the updated kernel on a Xen PVH dom0 or equivalent virtualized configuration that previously produced roots_per_node=0 and confirm the system no longer panics with a divide-by-zero; inspect dmesg for the new firmware bug warning only on bare-metal mismatches.

Typical attack path

  1. Gain ability to influence or control guest topology parameters on Xen or similar hypervisor
  2. Trigger Linux kernel boot or topology initialization on the dom0 or affected guest
  3. Force roots_per_node calculation to zero via num_nodes/num_roots mismatch
  4. Execute the modulo operation that divides by zero, inducing kernel panic

How to detect it

Review kernel logs (dmesg, /var/log/kern.log) on affected systems for divide-by-zero oops or panic messages during topology initialization; correlate with Xen PVH guest launches or migrations.

What your security team should do

  • Prioritize kernel updates for all Xen PVH and similar virtualized hosts within the next maintenance window
  • Test the updated kernel in a lab environment that reproduces the num_nodes=2/num_roots=1 condition before broad rollout
  • Monitor hypervisor topology reporting for anomalies that could produce zero roots_per_node
  • Document the change as a stability fix rather than a security patch for change-management records

The record

In the Linux kernel, the following vulnerability has been resolved: x86/amd_node: Avoid divide by zero on virtualized systems On a virtualized system, the number of nodes does not have a relationship to the number of roots. A Xen PVH dom0 can calculate roots_per_node as 0, which crashes with a divide by zero in: if (count++ % roots_per_node) because the underlying topology code on Xen ends up making num_nodes 2 and num_roots 1 and the integer division result is 0. The issue is seen with Xen, but it could affect other systems. Set roots_per_node to 1 in this case. Print a firmware bug when this is performed for non-virtualized systems. [ bp: Massage commit message. ]

Affected packages

Ecosystem Package Introduced Fixed