CVE-2026-23553: x86: incomplete IBPB for vCPU isolation
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.
Affected Software
Remediation
Patch Available
Patch Available
Patch Available
Event History
Frequently Asked Questions
What is the severity of CVE-2026-23553?
CVE-2026-23553 is considered a critical vulnerability due to its impact on task isolation within guest kernels.
How do I fix CVE-2026-23553?
To fix CVE-2026-23553, users should update to the latest patched version of Xen that addresses this vulnerability.
What does CVE-2026-23553 affect?
CVE-2026-23553 specifically affects the Xen hypervisor, particularly its context switch logic for virtual CPUs.
What are the implications of CVE-2026-23553?
The implications of CVE-2026-23553 include potential information leaks and security risks due to improper task isolation.
Is CVE-2026-23553 exploitable?
Yes, CVE-2026-23553 can be exploited to bypass isolation and access sensitive information across virtual machines.