dbcve.org
FreeBSDOperating system

CVE-2026-6386

MEDIUM · 6.2 CVSS v3.1 Published 2026-04-22
Mitigation only
No fix yet — a mitigation exists. There is no fixed release. A documented workaround reduces exposure in the meantime.
See remediation →
67/100
Remediation priority · Elevated
No privileges Zero-click

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 order to apply a particular protection key to an address range, the kernel must update the corresponding page table entries. The subroutine which handled this failed to take into account the presence of 1GB largepage mappings created using the shm_create_largepage(3) interface. In particular, it would always treat a page directory page entry as pointing to another page table page. The bug can be abused by an unprivileged user to cause pmap_pkru_update_range() to treat userspace memory as a page table page, and thus overwrite memory to which the application would otherwise not have access.

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 · moderate confidence

The pmap_pkru_update_range() kernel subroutine for applying protection keys to memory ranges fails to account for 1GB largepage mappings created via shm_create_largepage(3). It incorrectly treats all page directory entries as pointing to page table pages, allowing an unprivileged user to trick the function into treating userspace memory as a page table page and overwrite memory they should not access.

MitigationApply vendor-provided kernel patches that add proper validation for largepage mappings in pmap_pkru_update_range(); until patched, consider restricting access to shm_create_largepage(3) for unprivileged users.

Verify against the referenced sources before acting — the references below are authoritative for this CVE, this summary is not.

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
FreeBSDOperating system
Affected:= 13.5= 14.3= 14.4= 15.0

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
None
User interaction
None
Scope
Unchanged
Confidentiality
High
Integrity
None
Availability
None

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

Am I affected? How to checkSteps we derive from the advisory and the affected-version data, so you can decide whether this CVE reaches your setup. They are a guide, not a scan — your own configuration is the authority.

dbcve checks

Work through these to decide whether this CVE applies to you.

  1. Check FreeBSD version
    Run 'freebsd-version -k' or 'uname -r' to determine the running kernel version
    Affected if The version is 13.5, 14.3, 14.4, or 15.0 - these are the affected versions listed in the CVE
  2. Verify if largepage support is loaded or available
    Check for presence of the largepage subsystem: 'kldstat | grep largepage' or check kernel module availability with 'kldload -n largepage' (dry run)
    Affected if Largepage support is available in the kernel - this is required for the vulnerable code path to be exercised
  3. Determine if shm_create_largepage(3) is accessible to unprivileged users
    Check the security.shm.max user limits or examine if unprivileged processes can call shm_create_largepage - review sysctl 'kern.ipc.shm' settings or test with a non-root user attempting the call
    Affected if Unprivileged users can call shm_create_largepage(3) - the vulnerability requires an unprivileged user to be able to invoke this function to trigger the flawed pmap_pkru_update_range() code path
  4. Check if PKRU (Protection Keys) support is enabled
    Verify x86 PKRU feature presence: 'cpuctl identify 0' or check for 'pkru' in 'dmesg' output, or verify the CPU supports PKRU via 'sysctl hw.model' combined with CPU feature checks
    Affected if PKRU is enabled and in use on the system - the vulnerable function pmap_pkru_update_range() only executes when protection keys are being applied to memory ranges

A system is affected if it runs FreeBSD 13.5, 14.3, 14.4, or 15.0 AND has largepage support enabled AND allows unprivileged users to call shm_create_largepage(3) while PKRU protection keys are in use.

Generated from the published advisory. Verify against your own configuration.

Check your environment

Paste your version and any relevant configuration and it will be compared against the affected criteria above. Do not include secrets or credentials.

AI-assisted, checked against the advisory. Informational, not a guarantee.

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.

From vendor data
Mitigation available No clean upgrade yet — mitigate in the meantime
Mitigation

Apply vendor-provided kernel patches that add proper validation for largepage mappings in pmap_pkru_update_range(); until patched, consider restricting access to shm_create_largepage(3) for unprivileged users.

Fix this in FreeBSD Scoped from the published advisory
  • Consultation4.0 h
  • Implementation12.0 h
  • Testing8.0 h
  • Review / QA4.0 h
28.0 hours of engineering $4,880
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Scan for this in your stack

Free · runs locally
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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-2026-6386 in production — separate from our analysis above.

No notes yet

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What this is

A place for practitioners to share what actually worked: a mitigation you’ve tested, a configuration change, a version- or environment-specific caveat, or a link to a verified patch. The most useful notes rise to the top as peers upvote them, so the signal stays high.

What belongs here
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  • Version or environment caveats, and links to real fixes
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