CVE-2025-40300

medium

Published 2025-11-10 · Modified 2025-11-10

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CVSS v3

5.5

CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H

CVSS v4 NEW

—

not yet in upstream

VIR risk

5.5

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 ]

Predictions

Exploit likelihood

55%

Patch ETA

—

Heuristic predictions, AS-IS, for prioritization only.

Mitigations

No mitigations published for this CVE yet.

The vendor-content worker queues fetches as references arrive (check back in a few minutes). Or — if you've already worked around this in production — publish your fix to the community-verified tier.

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OS impact

Linux kernel Affected 2 releases

Version	Status	Fixed in
6.17	Affected	—
—	Affected	`3.17`

SUSE Affected 1 release

Version	Status	Fixed in
—	Affected	—

Debian Mixed 6 releases

Version	Status	Fixed in
trixie	Fixed	`6.12.48-1`
sid	Fixed	`6.16.7-1`
forky	Fixed	`6.16.7-1`
bullseye	Fixed	`5.10.244-1`
bookworm	Fixed	`6.1.153-1`
11.0	Affected	—

AlmaLinux Fixed 1 release

Version	Status	Fixed in
9	Fixed	`rtla-5.14.0-570.62.1.el9_6.aarch64.rpm`

Red Hat Fixed 2 releases

Version	Status	Fixed in
9	Fixed	—
8	Fixed	—

Rocky Linux Fixed 1 release

Version	Status	Fixed in
8	Fixed	—

References

Community-verified mitigations for this CVE will appear above when contributors publish them.

Verify integrity in audit chain (admin only). AS-IS.