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Linux KernelOperating system · Linux

CVE-2025-40300

MEDIUM · 5.5 CVSS v3.1 Published 2025-09-11
Fix available
A fix is available. Upgrade to 3.17 / 4.5 or later.
See remediation →
57/100
Remediation priority · Elevated
Zero-click Patch available

Official description Straight from the sourceThe vendor's or NVD's own wording, published unedited. Authoritative, but often terse — it says what broke, rarely what to do.

NVD · unedited
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 ]

Technical summary Written by usOur analysis, written from the advisory, the CVSS vector and the affected-version data. It adds context the advisory leaves out, and never invents facts that are not in the source.

dbcve analysis

A detailed technical summary for this CVE is being prepared.

Affected products & versions What the vendor confirmedThe version ranges the vendor confirmed as vulnerable. If your version sits inside a range here, treat yourself as exposed until you have upgraded.

NVD · CPE data
Linux KernelOperating system
Affected:>= 3.16.57, < 3.17>= 4.4.168, < 4.5>= 4.16, < 5.10.244>= 5.11, < 5.15.193>= 5.16, < 6.1.152>= 6.2, < 6.6.106>= 6.7, < 6.12.47>= 6.13, < 6.16.7= 6.17
Debian LinuxOperating system
Affected:= 11.0

CVSS breakdown How the score is builtThe industry scoring standard. It rates how the flaw is reached, what it takes to exploit, and what an attacker gains — the score is derived from those, not the other way round.

From the vector
Attack vector
Local
Complexity
Low
Privileges
Low
User interaction
None
Scope
Unchanged
Confidentiality
None
Integrity
None
Availability
High

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

Remediation Closing itWhat it takes to close this. Where a vendor fix exists we point at it; where none exists we say so plainly, and can build one. Effort estimates are scoped from the advisory, not from your codebase.

dbcve · scoped
Upgrade available Upgrade to 3.17 / 4.5 / 5.10.244 or later
Fixed in 3.174.55.10.244
Vendor patch git.kernel.org →
Recommended fix High confidence

Linux Kernel 5.10.244+ / 5.15.193+ / 6.1+ (or distribution-specific kernel package that includes the fix from commit 15006289e5c38b2a830e1fba221977a27598176c)

  1. Identify the current running kernel version using 'uname -r'
  2. Determine which kernel major version series you are running (e.g., 5.10.x, 5.15.x, 6.x)
  3. For kernel 5.10.x: upgrade to version 5.10.244 or later
  4. For kernel 5.11.x through 5.15.x: upgrade to version 5.15.193 or later
  5. For kernel 4.4.x: upgrade to version 4.5 or later
  6. For kernel 3.16.x: upgrade to version 3.17 or later
  7. Update the kernel package using the distribution's package manager (e.g., apt-get update && apt-get upgrade for Debian/Ubuntu, yum/dnf for RHEL)
  8. Reboot the system to load the new kernel
Caveat Kernel upgrades may require system downtime and could introduce compatibility issues with custom kernel modules or older drivers; test in staging environment first

Generated from the published advisory — verify against the referenced sources before acting.

We can perform the upgrade in your staging environment and verify nothing breaks — typical engagement from $1,600. Get the upgrade done

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References Go to the primary sourcePrimary sources — vendor advisories, patches and trackers. Where our summary and a reference disagree, the reference wins.

Primary sources

Practitioner notes

Contributed

Peer-ranked notes from engineers who’ve handled CVE-2025-40300 in production — separate from our analysis above.

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What this is

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What belongs here
  • Verified mitigations, workarounds, and config changes
  • Version or environment caveats, and links to real fixes
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