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.
Affected products
| Vendor | Product | Affected | Fixed |
|---|---|---|---|
| Xen | Xen | — | — |
Fixed in Linux distributions
Distributions backport fixes, so the version that fixes this vulnerability differs per release — upgrade to at least the version shown. From the distributions' security trackers and advisories.
Debian
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Debian 14 | xen | 4.20.2+37-g61ff35323e-1 | — |
| Debian 13 | xen | 4.20.2+37-g61ff35323e-0+deb13u1 | — |
| Debian 12 | xen | 4.17.7-0+deb12u1 | — |
Ubuntu
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 26.10 | xen | No fix yet | — |
| Ubuntu 26.04 LTS | xen | No fix yet | — |
| Ubuntu 25.10 | xen | No fix yet | — |
| Ubuntu 24.04 LTS | xen | No fix yet | — |
| Ubuntu 22.04 LTS | xen | No fix yet | — |
Show 3 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Ubuntu 20.04 LTS | xen | No fix yet | — |
| Ubuntu 18.04 LTS | xen | No fix yet | — |
| Ubuntu 16.04 LTS | xen | No fix yet | — |
SUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLES 15 SP7 | xen | 4.20.2_04-150700.3.22.1 | SUSE-SU-2026:0589-1, SUSE-SU-2026:0329-1 |
| SLES 12 SP5 | xen | 4.12.4_64-3.137.1 | SUSE-SU-2026:0328-1 |
Show 4 more (older releases, extended support, other products)Fewer releases
| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| SLE Micro 5.5 | xen | 4.17.6_04-150500.3.59.1 | SUSE-SU-2026:0304-1 |
| SLE Micro 5.4 | xen | 4.16.7_06-150400.4.78.1 | SUSE-SU-2026:0394-1 |
| SLE Micro 5.3 | xen | 4.16.7_06-150400.4.78.1 | SUSE-SU-2026:0394-1 |
| SLE Micro 5.2 | xen | 4.14.6_28-150300.3.94.1 | SUSE-SU-2026:0303-1 |
openSUSE
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| openSUSE Tumbleweed | xen | 4.21.0_04-1.1 | openSUSE-SU-2026:10118-1 |
| openSUSE Leap 15.6 | xen | 4.18.5_10-150600.3.37.1 | SUSE-SU-2026:0306-1 |
Alpine
Security tracker ↗| Release | Package | Fixed in | Advisory |
|---|---|---|---|
| Alpine v3.24 | xen | 4.21.0-r2 | — |
| Alpine v3.23 | xen | 4.20.2-r1 | — |
| Alpine v3.22 | xen | 4.20.2-r1 | — |
| Alpine v3.21 | xen | 4.19.4-r1 | — |
| Alpine v3.20 | xen | 4.18.5-r4 | — |
Advisories 9
- WID-SEC-2026-0229 Citrix Systems XenServer und Xen: Schwachstelle ermöglicht Offenlegung von Informationen BSI CERT-Bund (WID) · Oct 4, 2026
- openSUSE-SU-2026:10118-1 xen-4.21.0_04-1.1 on GA media SUSE / openSUSE Security Updates · Mar 23, 2026
- SUSE-SU-2026:0589-1 Security update for xen SUSE / openSUSE Security Updates · Mar 23, 2026
- SUSE-SU-2026:0328-1 Security update for xen SUSE / openSUSE Security Updates · Mar 23, 2026
- SUSE-SU-2026:0329-1 Security update for xen SUSE / openSUSE Security Updates · Mar 23, 2026
- SUSE-SU-2026:0304-1 Security update for xen SUSE / openSUSE Security Updates · Mar 23, 2026
- SUSE-SU-2026:0303-1 Security update for xen SUSE / openSUSE Security Updates · Mar 23, 2026
- SUSE-SU-2026:0306-1 Security update for xen SUSE / openSUSE Security Updates · Mar 23, 2026
- SUSE-SU-2026:0394-1 Security update for xen SUSE / openSUSE Security Updates · Feb 7, 2026