CVE-2026-23553 (GCVE-0-2026-23553)

Vulnerability from cvelistv5 – Published: 2026-01-28 15:33 – Updated: 2026-01-28 16:41
VLAI
Title
x86: incomplete IBPB for vCPU isolation
Summary
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.
Severity
2.9 (Low)
CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
SSVC
Exploitation: none Automatable: no Technical Impact: partial
CISA Coordinator (v2.0.3)
CWE
  • CWE-665 - Improper Initialization
  • CWE-693 - Protection Mechanism Failure
Assigner
XEN
References
Impacted products
Vendor Product Version
Xen Xen Unknown: consult Xen advisory XSA-479
Create a notification for this product.
Date Public
2026-01-27 12:00
Credits
This issue was discovered by David Kaplan of AMD.
Show details on NVD website
To clipboard 

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  • Seen: The vulnerability was mentioned, discussed, or observed by the user.
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