# CVE-2026-23553: xen: 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...

CVE-2026-23553 is fixed in xen on 1 platform, first by SUSE-SU-2026:0306-1, released January 27, 2026. It is not reported as exploited. Patch Radar priority: Routine.

- Web page: https://patchblox.com/security/cve/CVE-2026-23553
- Priority: Routine
- CVSS: 2.9 (low)
- EPSS: 0.0015
- CISA KEV: not listed
- Exploited (vendor report): no
- Publicly disclosed: no
- Published: Jan 27, 2026

## 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.

## Where it's fixed

| Platform | Product | Fixed in | Fix | Released |
|---|---|---|---|---|
| Linux | xen Debian 12.15 (bookworm) | 4.17.7-0+deb12u1 | [DEBIAN-CVE-2026-23553](https://patchblox.com/security/data/fix/linux/debian-cve-2026-23553.md) | Jan 28, 2026 |
| Linux | xen Debian 13.5 (trixie) | 4.20.2+37-g61ff35323e-0+deb13u1 | [DEBIAN-CVE-2026-23553](https://patchblox.com/security/data/fix/linux/debian-cve-2026-23553.md) | Jan 28, 2026 |
| Linux | xen Debian 14 | 4.20.2+37-g61ff35323e-1 | [DEBIAN-CVE-2026-23553](https://patchblox.com/security/data/fix/linux/debian-cve-2026-23553.md) | Jan 28, 2026 |
| Linux | xen opensuse-leap 15.6 | 4.18.5_10-150600.3.37.1 | [SUSE-SU-2026:0306-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-0306-1.md) | Jan 27, 2026 |
| Linux | xen sles 15.7 | 4.20.2_06-150700.3.25.1 | [SUSE-SU-2026:0589-1](https://patchblox.com/security/data/fix/linux/suse-su-2026-0589-1.md) | Feb 20, 2026 |

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Data as of 2026-11-09T13:31:49Z UTC. Source: Patchblox Patch Radar (https://patchblox.com/security/patch-radar). Patchblox finds out-of-date software on Windows, macOS and Linux and updates it through release rings: https://patchblox.com/demo

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