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CVE-2026-23553

x86: incomplete IBPB for vCPU isolation

Published: Jan 28, 2026Updated: Feb 9, 2026 Sources: CVE List NVDCWE-665
NVD MITRE
2.9CVSSLOW
EPSS Score
0.1%
Top 97.1%
CISA KEV
Not in KEV
Exploits
No Known Exploits
Remediation
Workaround Only

Description

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.

CVSS Vector Breakdown

AV:LAC:HPR:NUI:NS:UC:LI:NA:N
Exploitability
AV:LAttack Vector
Local
AC:HAttack Complexity
High
PR:NPrivileges Required
None
UI:NUser Interaction
None
Scope
S:UScope
Unchanged
Impact
C:LConfidentiality
Low
I:NIntegrity
None
A:NAvailability
None
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Weaknesses

CWE-665CWE-693

Affected Products

xenxen
On-prem
Cloud & SaaS / virtualization
XenXen
On-prem
Cloud & SaaS / virtualization
xenoss-projectGBCloud & SaaSaka xapi, qemu

Attack Graph

Products CVE Techniques Tactics

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Exploitability

Workaround Available

MITRE ATT&CK

1 technique
Privilege Escalation
View detailed technique mapping

References

https://xenbits.xenproject.org/xsa/advisory-479.html
xenbits.xenproject.org
http://www.openwall.com/lists/oss-security/2026/01/27/3
openwall.com
http://xenbits.xen.org/xsa/advisory-479.html
xenbits.xen.org

Timeline

Published
Jan 28, 2026
Last Updated
Feb 9, 2026

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