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Xen CVE-2026-23553

LOW
Improper Initialization (CWE-665)
2026-01-28 security@xen.org
2.9
CVSS 3.1 · NVD

Severity by source

NVD PRIMARY
2.9 LOW
AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Primary rating from NVD · only source for this CVE.

CVSS VectorNVD

Attack Vector
Local
Attack Complexity
High
Privileges Required
None
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
None

Lifecycle Timeline

3
Analysis Generated
Mar 12, 2026 - 21:54 vuln.today
Patch released
Feb 09, 2026 - 18:46 nvd
Patch available
CVE Published
Jan 28, 2026 - 16:16 nvd
LOW 2.9

DescriptionCVE.org

In the context switch logic Xen attempts to skip an IBPB in the case of a vCPU returning to a CPU on which it was the previous vCPU to run. While safe for Xen's isolation between vCPUs, this prevents the guest kernel correctly isolating between tasks. Consider:

  1. vCPU runs on CPU A, running task 1.
  2. vCPU moves to CPU B, idle gets scheduled on A. Xen skips IBPB.
  3. On CPU B, guest kernel switches from task 1 to 2, issuing IBPB.
  4. vCPU moves back to CPU A. Xen skips IBPB again.

Now, task 2 is running on CPU A with task 1's training still in the BTB.

AnalysisAI

In the context switch logic Xen attempts to skip an IBPB in the case of a vCPU returning to a CPU on which it was the previous vCPU to run. While safe for Xen's isolation between vCPUs, this prevents the guest kernel correctly isolating between tasks. [CVSS 2.9 LOW]

Technical ContextAI

Affects Xen. In the context switch logic Xen attempts to skip an IBPB in the case of a vCPU returning to a CPU on which it was the previous vCPU to run. While safe for Xen's isolation between vCPUs, this prevents the guest kernel correctly isolating between tasks. Consider:

  1. vCPU runs on CPU A, running task 1.
  2. vCPU moves to CPU B, idle gets scheduled on A. Xen skips IBPB.
  3. On CPU B, guest kernel switches from task 1 to 2, issuing IBPB.
  4. vCPU moves back to CPU A. Xen skips IBPB again.

Now, t

RemediationAI

A vendor patch is available — apply it immediately.

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CVE-2026-23553 vulnerability details – vuln.today

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