Vulnerability Description
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 Score
LOW
Affected Products
| Vendor | Product | Versions |
|---|---|---|
| Xen | Xen | >= 4.6.0 |
Related Weaknesses (CWE)
References
- https://xenbits.xenproject.org/xsa/advisory-479.htmlMitigationPatchVendor Advisory
- http://www.openwall.com/lists/oss-security/2026/01/27/3Mailing ListMitigationPatch
- http://xenbits.xen.org/xsa/advisory-479.htmlMitigationPatchVendor Advisory
FAQ
What is CVE-2026-23553?
CVE-2026-23553 is a vulnerability with a CVSS score of 2.9 (LOW). 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 ...
How severe is CVE-2026-23553?
CVE-2026-23553 has been rated LOW with a CVSS base score of 2.9/10. Review the CVSS metrics above for detailed severity breakdown.
Is there a patch for CVE-2026-23553?
Check the references section above for vendor advisories and patch information. Affected products include: Xen Xen.