Vulnerability Report

CVE-2026-23553

Title: IBPB Skip Vulnerability in Xen

Other

Proof Of Concept

No public PoC currently indexed for CVE-2026-23553.

CWE Category NVD-CWE-noinfo

Published Date Jan 28, 2026

Modified Date Feb 09, 2026

Exploit Status Not Found

Score 2.9 CVSS v

Exploit Probability (EPSS)

0.13%

Vulnerability Summary

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. 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.

Impacted Vendors

xen 1

xensource_inc 1

Reference Links

https://xenbits.xenproject.org/xsa/advisory-479.html

CVSS v3.1

Source Entity 134c704f-9b21-4f2e-91b3-4a467353bcc0

Severity LOW

2.9

Attack Vector

LOCAL

Complexity

HIGH

Privileges

N/A

Interaction

NONE

Confidentiality

N/A

Integrity

N/A

Availability

N/A

Scope

UNCHANGED

RAW VECTOR CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N

Associated Attack Patterns (CAPEC)

Total: Patterns