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.
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
| Product | Fixed in | Fix | Released |
|---|---|---|---|
| Linux | |||
| xen · Debian 12.15 (bookworm) | 4.17.7-0+deb12u1 | DEBIAN-CVE-2026-23553 | Jan 28, 2026 |
| xen · Debian 13.5 (trixie) | 4.20.2+37-g61ff35323e-0+deb13u1 | DEBIAN-CVE-2026-23553 | Jan 28, 2026 |
| xen · Debian 14 | 4.20.2+37-g61ff35323e-1 | DEBIAN-CVE-2026-23553 | Jan 28, 2026 |
| xen · opensuse-leap 15.6 | 4.18.5_10-150600.3.37.1 | SUSE-SU-2026:0306-1 | Jan 27, 2026 |
| xen · sles 15.7 | 4.20.2_06-150700.3.25.1 | SUSE-SU-2026:0589-1 | Feb 20, 2026 |
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