CVE-2025-40300 - CVE House
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Status published Unknown CVE-2025-40300

x86/vmscape: Add conditional IBPB mitigation

Vulnerability Description

In the Linux kernel, the following vulnerability has been resolved: x86/vmscape: Add conditional IBPB mitigation VMSCAPE is a vulnerability that exploits insufficient branch predictor isolation between a guest and a userspace hypervisor (like QEMU). Existing mitigations already protect kernel/KVM from a malicious guest. Userspace can additionally be protected by flushing the branch predictors after a VMexit. Since it is the userspace that consumes the poisoned branch predictors, conditionally issue an IBPB after a VMexit and before returning to userspace. Workloads that frequently switch between hypervisor and userspace will incur the most overhead from the new IBPB. This new IBPB is not integrated with the existing IBPB sites. For instance, a task can use the existing speculation control prctl() to get an IBPB at context switch time. With this implementation, the IBPB is doubled up: one at context switch and another before running userspace. The intent is to integrate and optimize these cases post-embargo. [ dhansen: elaborate on suboptimal IBPB solution ]

Impact Analysis

Refer to official advisory for detailed impact metrics.

Remediation

Ensure systems are updated to the latest vendor-supplied patch levels.

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Credits & Attribution

No credits recorded in the NVD database.

References

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Affected Vendor

Affected Software

Linux
Vulnerable Versions:
15d45071523d89b3fb7372e2135fbd72f6af9506, c51f1e5f57cca88d8d5894b6fad1638f643a99d0, 4b3870c343a82cd2df7192cc5149c87205dcc611, 3.16.57, 4.4.168, 4.16, 0, 5.10.244, 5.15.193, 6.1.152, 6.6.106, 6.12.47, 6.16.7, 6.17

Timeline

Official Publish: September 11th, 2025
Last Modified: July 14th, 2026
Added to House: July 22nd, 2026

CVSS Vectors

No vector data available

Weaknesses (CWE)

No CWE data available

MITRE ATT&CK TTPs

No associated TTPs found for this vulnerability.