CVE-2026-23553 Affecting xen package, versions <4.20.2+37-g61ff35323e-0+deb13u1


Severity

Recommended
low

Based on default assessment until relevant scores are available.

Threat Intelligence

EPSS
0.13% (3rd percentile)

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  • Snyk IDSNYK-ECHOLATEST-XEN-18388962
  • published29 Jul 2026
  • disclosed28 Jan 2026

Introduced: 28 Jan 2026

CVE-2026-23553  (opens in a new tab)

How to fix?

Upgrade Echo:latest xen to version 4.20.2+37-g61ff35323e-0+deb13u1 or higher.

NVD Description

Note: Versions mentioned in the description apply only to the upstream xen package and not the xen package as distributed by Echo. See How to fix? for Echo:latest 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