Vulnerability in Xen
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.
Vulnerability class: Dirty Pipe (CVE-2022-0847)
EPSS: 0.001 (3.0th percentile) — read the EPSS interpretation.
CVSS v3 metric
CVSS v3 base score 2.9 (Low). Vector: CVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N.
Affected products
- Xen — versions consult Xen advisory XSA-479
Weakness classification (CWE)
References
- security@xen.org (Patch, Mitigation, Vendor Advisory)
- af854a3a-2127-422b-91ae-364da2661108 (Mailing List, Mitigation, Patch, Third Party Advisory)
- af854a3a-2127-422b-91ae-364da2661108 (Mitigation, Patch, Vendor Advisory)
Frequently asked questions
- What is CVE-2026-23553?
- CVE-2026-23553 is a low-severity vulnerability in Xen, classified under Improper Initialization. CVSS score: 2.9/10. Published 2026-01-28.
- How severe is CVE-2026-23553?
- Low severity. CVSS v3 base score is 2.9 out of 10.