CVE-2026-23553
2.9
LOW
CVSS 3.1
EPSS 0.03%
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.
How to fix CVE-2026-23553
To remediate CVE-2026-23553, upgrade the affected package to a fixed version below.
- —upgrade to 4.18.5-r4 or later
- —no fix listed
Is CVE-2026-23553 being exploited?
Low — EPSS is 0.0%, meaning exploitation activity has not been observed at scale.
Affected packages (2)
- from 0, < 4.18.5-r4
- from 0
CVSS scores
| Source | Version | Severity | Vector |
|---|---|---|---|
| osv | CVSS 3.1 | LOW2.9 | CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N |