CVE-2026-23553

low-risk

Published 2026-01-28

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.

Do I need to act?

0.03% chance of exploitation

EPSS score — low exploit probability

Not on CISA KEV list

No confirmed active exploitation reported to CISA

Patch status unknown

Check vendor advisories for fix availability and mitigation guidance

CVSS 2.9/10 Low

LOCAL / HIGH complexity

Affected Products (1)

Xen

Affected Vendors

Xen

References (3)

Mitigation https://xenbits.xenproject.org/xsa/advisory-479.html

Mailing List http://www.openwall.com/lists/oss-security/2026/01/27/3

Mitigation http://xenbits.xen.org/xsa/advisory-479.html

/ 100

low-risk

Severity 8/34 · Low

Exploitability 0/34 · Minimal

Exposure 5/34 · Minimal