CVE-2026-23553

2.9 lowEPSS 0.1%

Low (2.9) in xen xen. EPSS 0.1% chance of exploitation in the next 30 days.

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

CVSS 3.1

2.9 low

CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

EPSS: 0.1% chance of exploitation in the next 30 days; higher than 3% of CVEs (scores of 2026-10-31)
CWEs: CWE-665, CWE-693
Published: 2026-01-28
Modified: 2026-06-17
Record from: the NVD, synced 2026-10-19

Affected

xen:xen

References

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

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