CVE-2026-23553
Fixed in a distro release EPSS <1%CVSS 2.9
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.
Products: xen
Distro releases
| Release | Package | Fixed in |
|---|---|---|
| Alpine 3.20 | xen | 4.18.5-r4 |
| Alpine 3.21 | xen | 4.19.4-r1 |
| Alpine 3.22 | xen | 4.20.2-r1 |
| Alpine 3.23 | xen | 4.20.2-r1 |
| Alpine 3.24 | xen | 4.21.0-r2 |
| Debian 12 | xen | 4.17.7-0+deb12u1 |
| Debian 13 | xen | 4.20.2+37-g61ff35323e-0+deb13u1 |
| Debian 14 | xen | 4.20.2+37-g61ff35323e-1 |
| SUSE Linux Enterprise Micro 5.2 | xen | 4.14.6_28-150300.3.94.1 |
| SUSE Linux Enterprise Micro 5.3 | xen | 4.16.7_06-150400.4.78.1 |
| SUSE Linux Enterprise Micro 5.4 | xen | 4.16.7_06-150400.4.78.1 |
| SUSE Linux Enterprise Micro 5.5 | xen | 4.17.6_04-150500.3.59.1 |
| SUSE Linux Enterprise Module for Basesystem 15 SP7 | xen | 4.20.2_06-150700.3.25.1 |
| SUSE Linux Enterprise Module for Basesystem 15 SP7 | xen | 4.20.2_04-150700.3.22.1 |
| SUSE Linux Enterprise Module for Server Applications 15 SP7 | xen | 4.20.2_06-150700.3.25.1 |
| SUSE Linux Enterprise Module for Server Applications 15 SP7 | xen | 4.20.2_04-150700.3.22.1 |
| SUSE Linux Enterprise Server LTSS Extended Security 12 SP5 | xen | 4.12.4_64-3.137.1 |
| Ubuntu 16.04 LTS | xen | no fix |
| Ubuntu 18.04 LTS | xen | no fix |
| Ubuntu 20.04 LTS | xen | no fix |
| Ubuntu 22.04 LTS | xen | no fix |
| Ubuntu 24.04 LTS | xen | no fix |
| Ubuntu 25.10 | xen | no fix |
| Ubuntu 26.04 LTS | xen | no fix |
| Ubuntu 26.10 | xen | no fix |
| openSUSE Leap 15.6 | xen | 4.18.5_10-150600.3.37.1 |
| openSUSE Tumbleweed | xen | 4.21.0_04-1.1 |