CVE-2026-23553
Publication date 28 January 2026
Last updated 4 February 2026
Ubuntu priority
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.
Status
| Package | Ubuntu Release | Status |
|---|---|---|
| xen | 25.10 questing |
Needs evaluation
|
| 24.04 LTS noble |
Needs evaluation
|
|
| 22.04 LTS jammy |
Needs evaluation
|
|
| 20.04 LTS focal |
Needs evaluation
|
|
| 18.04 LTS bionic |
Needs evaluation
|
|
| 16.04 LTS xenial |
Needs evaluation
|
Notes
mdeslaur
hypervisor packages are in universe. For issues in the hypervisor, add appropriate tags to each section, ex: Tags_xen: universe-binary
Severity score breakdown
| Parameter | Value |
|---|---|
| Base score |
2.9 · Low
|
| Attack vector | Local |
| Attack complexity | High |
| Privileges required | None |
| User interaction | None |
| Scope | Unchanged |
| Confidentiality | Low |
| Integrity impact | None |
| Availability impact | None |
| Vector | CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N |