CVE-2025-40300

Medium

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 ]

Package Linux Kernel
Published 2025-09-11
Last modified 2026-05-12
CVSS version 3.1
Patch available
Yes

CVSS 3.1 score

5.5

out of 10
Medium
Attack Vector
Local
Attack Complexity
Low
Privileges Required
Low
User Interaction
None
Scope
Unchanged
Confidentiality
Low
Integrity
None
Availability
High
Vector string
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

Affected versions

Linux kernel versions 3.16.57, 4.4.168, 4.16 and later are affected. Fixed in 5.10.244, 5.15.193, 6.1.152, 6.6.106, 6.12.47, 6.16.7, 6.17 and their respective stable series.

Affected from
≥ 3.16.57 ≥ 4.4.168 ≥ 4.16
Fixed in
✓ 5.10.244 5.10.x ✓ 5.15.193 5.15.x ✓ 6.1.152 6.1.x ✓ 6.6.106 6.6.x ✓ 6.12.47 6.12.x ✓ 6.16.7 6.16.x ✓ 6.17

References

The following references provide additional information about CVE-2025-40300 including vendor advisories, patch commits, exploit details, and third-party analysis. Links are sourced from the NIST NVD database.

13 patch commits total View all on NVD

Frequently asked questions

  • What is CVE-2025-40300?

    CVE-2025-40300 is a Medium severity Linux kernel vulnerability with a CVSS score of 5.5 out of 10 . It affects Linux kernel versions from 3.16.57 onward and has been patched in 5.10.244, 5.15.193, 6.1.152 and others. CVE-2025-40300 has not been confirmed as actively exploited and is not listed in the CISA KEV catalog.

  • What is the CVSS score for CVE-2025-40300?

    CVE-2025-40300 has a CVSS score of 5.5 out of 10, rated Medium severity (CVSS 3.1). The vector string is CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H .

  • Is there a patch available for CVE-2025-40300?

    Yes — CVE-2025-40300 has been patched. Fixed versions include 5.10.244, 5.15.193, 6.1.152 and others. If you are running Linux kernel 3.16.57 or later up to the fix versions, apply the relevant patch for your kernel branch.

  • Is CVE-2025-40300 actively exploited?

    No — CVE-2025-40300 has not been confirmed as actively exploited. It is not listed in the CISA Known Exploited Vulnerabilities (KEV) catalog.

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