# CVE-2026-6386: Missing large page handling in pmap_pkru_update_range()

> An unprivileged user can exploit missing large page handling in the FreeBSD kernel to overwrite protected memory, potentially leading to privilege escalation.

- **Severity:** Medium 6.2 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:N/A:N`)
- **Exploited in the wild:** Not known
- **Login needed:** Not needed
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 22 Apr 2026
- **Updated:** 22 Apr 2026
- **Also known as:** GHSA-99g5-mwj2-6xjq

## What is CVE-2026-6386?

CVE-2026-6386 is a medium-severity vulnerability in Freebsd Freebsd, published on 22 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

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.

Weakness: CWE-732 (Incorrect Permission Assignment for Critical Resource), CWE-269 (Improper Privilege Management)

## Which versions are affected by CVE-2026-6386?

It affects 1 product.


Products: Freebsd Freebsd.

## How do I fix CVE-2026-6386?

No fix has been published for CVE-2026-6386 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-6386 being exploited?

There is no known exploitation of CVE-2026-6386 in the wild and no public exploit code.

## Other vulnerabilities in Freebsd Freebsd

- [CVE-2018-17160](https://insights.sbomify.com/CVE-2018-17160/): Memory corruption in FreeBSD (critical 10.0)
- [CVE-2014-3954](https://insights.sbomify.com/CVE-2014-3954/): Memory corruption in n/a (critical 10.0)
- [CVE-2006-4304](https://insights.sbomify.com/CVE-2006-4304/): Memory corruption in n/a (critical 10.0)
- [CVE-2006-0226](https://insights.sbomify.com/CVE-2006-0226/): Integer overflow in n/a (critical 10.0)
- [CVE-2004-0002](https://insights.sbomify.com/CVE-2004-0002/): Denial of service in n/a (critical 10.0)

## Fix prompt for AI coding agents

```text
Check this codebase for CVE-2026-6386 and fix it if it is affected.

What it is: CVE-2026-6386 is a medium-severity vulnerability in Freebsd Freebsd, published on 22 Apr 2026. It can only be exploited from the same machine or local network, with no action from the victim.
Exploitation: There is no known exploitation of CVE-2026-6386 in the wild and no public exploit code.

Affected product: Freebsd Freebsd. No package-level version data is available, so check the vendor advisory linked from the reference page.

Task:
1. Search the dependency manifests and lockfiles (for example package.json, package-lock.json, requirements.txt, poetry.lock, uv.lock, pom.xml, build.gradle, go.mod, Cargo.lock, Gemfile.lock) and any Dockerfiles for the affected packages, including transitive dependencies.
2. If an affected version is in use, upgrade it to the fixed version for its release line with the project's package manager, so the lockfile is regenerated. Prefer the smallest upgrade that fixes it.
3. If there is no fix, or the upgrade would break the build, do not guess: explain the risk and the safest workaround instead.
4. Run the tests and summarise what changed and why.
5. If nothing in the project is affected, say so and change nothing.

Reference: https://insights.sbomify.com/CVE-2026-6386/ (Markdown: https://insights.sbomify.com/CVE-2026-6386/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-6386
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-6386
- OSV: https://osv.dev/vulnerability/CVE-2026-6386

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-6386/
Summaries are generated and may contain mistakes; the official description above is the record.