CVE-2025-40300 | x86/vmscape: Add conditional IBPB mitigation

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 ]

Published: 2025-09-11 Last update: 2026-05-12 Assigner: 416baaa9-dc9f-4396-8d5f-8c081fb06d67 Source: 416baaa9-dc9f-4396-8d5f-8c081fb06d67
NVD Status：Modified，CVE State: published
View at NVD, CVE.org, EUVD

CVE-2025-40300 is rated Low Risk (25.6/100): CVSS Medium severity, with low exploitation likelihood (EPSS 0.04%). Monitor for updates and reassess as exploit intelligence or EPSS changes.

Risk is dynamic; we continuously reassess and refresh what is shown on this page as upstream context changes.

Exploit prediction scoring system (EPSS) score for CVE-2025-40300

EPSS lead: Daily EPSS estimates relative likelihood of exploitation; percentile ranks this CVE among scored vulnerabilities (higher = more severe relative rank).

# Date Old EPSS score New EPSS score Delta (New - Old)
1 2026-01-17 0.08% 0.04% -0.04%
2 2025-10-17 0.03% 0.08% +0.04%
3 2025-09-12 — 0.03% —

Full EPSS history (3 records total)

Common vulnerability scoring system (CVSS) metrics for CVE-2025-40300

CVSS metrics for this CVE.

Base score Version Severity Vector Exploitability Impact Score source
5.5 3.1 MEDIUM
CVSS:3.1/AV:L/AC:L/PR:L/UI:N/S:U/C:N/I:N/A:H Click to expand
Attack vector (AV:L)
They already need access on the box, or another person has to do something wrong; it’s not a remote drive-by.
Attack complexity (AC:L)
Once they can reach the bug, pulling it off is straightforward—no weird race conditions or rare setup.
Privileges required (PR:L)
A normal user session is enough; they don’t have to be admin.
User interaction (UI:N)
Nobody has to click “OK” or open a trap file; it can work without a victim helping.
Scope (S:U)
Damage stays in the same “trust bubble” as the broken component—no big spill into unrelated systems.
Confidentiality (C:N)
Doesn’t really leak secrets in a meaningful way.
Integrity (I:N)
Data isn’t meaningfully altered or forged.
Availability (A:H)
Could take the service down hard or make it unusable for people who depend on it.
 1.8 3.6 [email protected]

Weakness enumeration for CVE-2025-40300

GitHub Security Advisory for CVE-2025-40300

GHSA-x8qw-46ww-c957 · Severity: medium — In the Linux kernel, the following vulnerability has been resolved: x86/vmscape: Add conditional...

OS Trackers for CVE-2025-40300

vendor priority summary link
debian not yet assigned CVE-2025-40300 not yet assigned priority: Debian including 2 source packages (linux, linux-6.1), 6 status rows across 5 suites (bookworm, bullseye, forky, sid, trixie): resolved 6. https://security-tracker.debian.org/tracker/CVE-2025-40300
redhat medium — https://access.redhat.com/security/cve/CVE-2025-40300
suse medium — https://www.suse.com/security/cve/CVE-2025-40300/
ubuntu high CVE-2025-40300 high priority: Ubuntu including 158 source packages (linux, linux-allwinner-5.19, …), 1414 status rows across 9 suites (bionic, focal, jammy, noble, plucky, questing, trusty, upstream, xenial): DNE 1017, released 211, ignored 161, not-affected 17, needs-triage 4, needed 3, pending 1. https://ubuntu.com/security/CVE-2025-40300

Affected software / configurations for CVE-2025-40300

Vendor Product Version Raw CPE
linux linux_kernel >= 3.16.57, < 3.17 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 4.4.168, < 4.5 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 4.16, < 5.10.244 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.11, < 5.15.193 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 5.16, < 6.1.152 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.2, < 6.6.106 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.7, < 6.12.47 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel >= 6.13, < 6.16.7 cpe:2.3:o:linux:linux_kernel:*:*:*:*:*:*:*:*
linux linux_kernel 6.17 cpe:2.3:o:linux:linux_kernel:6.17:rc1:*:*:*:*:*:*
linux linux_kernel 6.17 cpe:2.3:o:linux:linux_kernel:6.17:rc2:*:*:*:*:*:*
linux linux_kernel 6.17 cpe:2.3:o:linux:linux_kernel:6.17:rc3:*:*:*:*:*:*
linux linux_kernel 6.17 cpe:2.3:o:linux:linux_kernel:6.17:rc4:*:*:*:*:*:*
linux linux_kernel 6.17 cpe:2.3:o:linux:linux_kernel:6.17:rc5:*:*:*:*:*:*
debian debian_linux 11.0 cpe:2.3:o:debian:debian_linux:11.0:*:*:*:*:*:*:*

References for CVE-2025-40300

URL Tags
https://git.kernel.org/stable/c/15006289e5c38b2a830e1fba221977a27598176c Patch
https://git.kernel.org/stable/c/2f4f2f8f860cb4c3336a7435ebe8dcfded0c9c6e Patch
https://git.kernel.org/stable/c/2f8f173413f1cbf52660d04df92d0069c4306d25 Patch
https://git.kernel.org/stable/c/34e5667041050711a947e260fc9ebebe08bddee5 Patch
https://git.kernel.org/stable/c/459274c77b37ac63b78c928b4b4e748d1f9d05c8 Patch
https://git.kernel.org/stable/c/510603f504796c3535f67f55fb0b124a303b44c8 Patch
https://git.kernel.org/stable/c/893387c18612bb452336a5881da0d015a7e8f4a2 Patch
https://git.kernel.org/stable/c/9c23a90648e831d611152ac08dbcd1283d405e7f Patch
https://git.kernel.org/stable/c/ac60717f9a8d21c58617d0b34274babf24135835 Patch
https://git.kernel.org/stable/c/c08192b5d6730a914dee6175bc71092ee6a65f14 Patch
https://git.kernel.org/stable/c/d5490dfa35427a2967e00a4c7a1b95fdbc8ede34 Patch
https://git.kernel.org/stable/c/d7ddc93392e4a7ffcccc86edf6ef3e64c778db52 Patch
https://git.kernel.org/stable/c/f866eef8d1c65504d30923c3f14082ad294d0e6d Patch
http://www.openwall.com/lists/oss-security/2025/11/14/3 Mailing List
http://www.openwall.com/lists/oss-security/2025/11/14/4 Mailing List
http://www.openwall.com/lists/oss-security/2025/11/14/6 Mailing List
http://www.openwall.com/lists/oss-security/2025/11/17/2 Mailing List
http://www.openwall.com/lists/oss-security/2025/11/17/3 Mailing List
https://lists.debian.org/debian-lts-announce/2025/10/msg00007.html Third Party Advisory
https://lists.debian.org/debian-lts-announce/2025/10/msg00008.html Third Party Advisory
https://cert-portal.siemens.com/productcert/html/ssa-032379.html
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