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

Routine

LOW 2.9MITIGATE

CVE-2026-23553 is a low-severity flaw (CVSS 2.9) affecting xen. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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 m

Why this priority

No elevated risk signals yet

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	2.9 (Low)
Attack vector	Local
Attack complexity	High
Privileges needed	None
User interaction	None
EPSS exploit chance	0.1% (top 96%)
CISA exploited list	No
Weakness	CWE-665, CWE-693
Published	2026-01-28
Last modified	2026-06-17

Publisher (CNA): Xen Project · Vendor: xen

Last updated 2026-06-17 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-01-28 16:16 UTCPublished CVE record published
2026-06-17 10:21 UTCUpdated Record last modified

xen xen MITIGATE

Affected: >= 4.6.0

Fixed in: no fixed release known

Safe to downgrade to: a release before 4.6.0

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-23553?

xen: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-23553 being exploited?

CVE-2026-23553 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-23553 affect?

CVE-2026-23553 affects xen. Severity is low (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 bet

How urgent is CVE-2026-23553?

Priority 11/100. No elevated risk signals yet.

Software pages

Xen vulnerabilities

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References

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