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.
Does this matter?
Lower severity and a low EPSS score (0.14%). Track it; it rarely justifies an emergency change on its own.
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 3.1
- 2.9 LOWCVSS:3.1/AV:L/AC:H/PR:N/UI:N/S:U/C:L/I:N/A:N
- EPSS
- 0.14% probability · 4th percentile
- Public exploits
- None in Exploit-DB
- CISA KEV
- Not listed
- Weakness
- CWE-665, CWE-693
- Affected
- xen/xen
- Source
- security@xen.org
EPSS 0.1% since 27 October 2026; no change recorded yet. Points are recorded when the score first appears and whenever it moves by a percentage point or more.
References
- https://xenbits.xenproject.org/xsa/advisory-479.htmlMitigation, Patch, Vendor Advisory
- http://www.openwall.com/lists/oss-security/2026/01/27/3Mailing List, Mitigation, Patch, Third Party Advisory
- http://xenbits.xen.org/xsa/advisory-479.htmlMitigation, Patch, Vendor Advisory
Source: NVD record, EPSS from FIRST.org, KEV from CISA, exploits from Exploit-DB. Refreshed daily. Download this record as JSON.