CVE-2026-23553
published 2026-01-28CVE-2026-23553: 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…
PriorityP410low2.9CVSS 3.1
AVLACHPRNUINSUCLINAN
EPSS
0.13%
3.0th percentile
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
8 ranges
| Vendor | Product | Version range | Fixed in |
|---|---|---|---|
| debian | xen | < xen 4.20.2+37-g61ff35323e-1 (forky) | xen 4.20.2+37-g61ff35323e-1 (forky) |
| xen | xen | >= 0 < 4.18.5-r4 | 4.18.5-r4 |
| xen | xen | >= 0 < 4.19.4-r1 | 4.19.4-r1 |
| xen | xen | >= 0 < 4.20.2-r1 | 4.20.2-r1 |
| xen | xen | >= 0 < 4.20.2-r1 | 4.20.2-r1 |
| xen | xen | >= 0 < 4.20.2+37-g61ff35323e-0+deb13u1 | 4.20.2+37-g61ff35323e-0+deb13u1 |
| xen | xen | >= 0 < 4.20.2+37-g61ff35323e-1 | 4.20.2+37-g61ff35323e-1 |
| xen | xen | >= 4.6.0 | — |
CVSS provenance
nvdv3.12.9LOWCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
osv2.9LOW
vendor_debian2.9LOW
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Debian
CVE-2026-23553: xen - In the context switch logic Xen attempts to skip an IBPB in the case of a vCPU r...
vendor_debian·2026·CVSS 2.9
CVE-2026-23553 [LOW] CVE-2026-23553: xen - In the context switch logic Xen attempts to skip an IBPB in the case of a vCPU r...
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.
Scope: local
bookworm: open
bullseye: open
forky: resolved (fixed in 4.20.2+37-g61ff35323e-1)
sid: resolved (fixed in 4.20.2+37-g61ff35323e-1)
trixie: resolved (fixed in 4.20.2+37-g61ff35323e-0+deb13u1)
OSV
CVE-2026-23553: 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
osv·2026-01-28·CVSS 2.9
CVE-2026-23553 [LOW] CVE-2026-23553: 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
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.
GHSA
GHSA-pxqc-5jg3-xfqm: 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
ghsa_unreviewed·2026-01-28
CVE-2026-23553 [LOW] CWE-665 GHSA-pxqc-5jg3-xfqm: 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
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.
OSV
CVE-2026-23553: 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
osv·2026-01-28·CVSS 2.9
CVE-2026-23553 [LOW] CVE-2026-23553: 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
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.
No detection rules found.
No public exploits indexed.
2026-01-28
Published