Executive Summary

This vulnerability exists in the FreeBSD amd64 kernel's handling of memory protection keys (pkru), specifically in the function pmap_pkru_update_range().

The function is supposed to update page table entries to apply protection keys to memory regions. However, it incorrectly assumes that a page directory entry always points to a page table page and does not properly handle 1GB large page mappings created via the shm_create_largepage(3) interface.

Because of this, an unprivileged user can exploit the bug to trick the function into treating user-space memory as a page table page, which can lead to overwriting memory areas that should be protected.

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Impact Analysis

An unprivileged user can exploit this vulnerability to cause the kernel to overwrite memory regions that the application or user should not have access to.

This can lead to unauthorized memory modification, potentially allowing privilege escalation or other malicious actions that compromise system security.

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Detection Guidance

There are no specific detection commands or network indicators provided for this vulnerability. It is a kernel-level issue related to memory protection key handling in FreeBSD amd64 systems.

Detection would primarily involve verifying the FreeBSD system version and whether the system has been updated with the patches addressing CVE-2026-6386.

You can check your FreeBSD version with the command: `freebsd-version`.

To verify if the system is patched, you may compare installed patches or check the update history, but no direct commands to detect exploitation or presence of the vulnerability are provided.

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Mitigation Strategies

The immediate mitigation step is to upgrade your FreeBSD system to a patched version released on or after April 21, 2026.

• If using pkg(8) for base system package installations, run: `pkg upgrade -r FreeBSD-base` and then reboot the system.
• If using freebsd-update(8) for binary distribution set installations, run: `freebsd-update fetch` and `freebsd-update install` followed by a reboot.
• Alternatively, apply the source code patches manually by downloading the appropriate patch for your FreeBSD version, verifying its PGP signature, applying it to the source tree, recompiling the kernel, and rebooting.

No workaround is available other than applying these updates or patches.

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Compliance Impact

This vulnerability allows an unprivileged user to overwrite memory areas that should be protected, potentially leading to unauthorized access or modification of sensitive data.

Such unauthorized memory access and modification could compromise the confidentiality and integrity of data, which are critical requirements under common standards and regulations like GDPR and HIPAA.

Therefore, if exploited, this vulnerability could lead to non-compliance with these regulations due to potential data breaches or unauthorized data manipulation.

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