CVE-2026-23553 Affecting xen-tools package, versions <4.20.2_06-150700.3.25.1


Severity

Recommended
0.0
medium
0
10

Based on SUSE Linux Enterprise Server security rating.

Threat Intelligence

EPSS
0.13% (3rd percentile)

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  • Snyk IDSNYK-SLES157-XENTOOLS-15325177
  • published21 Feb 2026
  • disclosed20 Feb 2026

Introduced: 20 Feb 2026

CVE-2026-23553  (opens in a new tab)

How to fix?

Upgrade SLES:15.7 xen-tools to version 4.20.2_06-150700.3.25.1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream xen-tools package and not the xen-tools package as distributed by SLES. See How to fix? for SLES:15.7 relevant fixed versions and status.

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.

CVSS Base Scores

version 3.1