# CVE-2026-58083: Use-after-free in kqueue copy-on-fork

> An unprivileged local user can trigger a use-after-free in the FreeBSD kernel during fork, potentially leading to privilege escalation.

- **Severity:** High 8.4 (`CVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H`)
- **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:** 19 Aug 2026
- **Updated:** 20 Aug 2026
- **Also known as:** GHSA-j94h-9p69-vhvm

## What is CVE-2026-58083?

CVE-2026-58083 is a high-severity use after free vulnerability in Freebsd Freebsd, published on 19 Aug 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

While the kernel was copying knotes during fork, a knote with a timer-based filter could fire and be enqueued on the kqueue's active list before the copy was complete.  The copy routine did not account for this and could enqueue the new knote a second time, corrupting the active list.  In addition, the copy routine did not hold the appropriate locks while reading knote state, allowing further races.

An unprivileged local user can trigger a use-after-free in the kernel, potentially leading to privilege escalation.

Weakness: CWE-416 (Use After Free)

## Which versions are affected by CVE-2026-58083?

It affects 1 product.


Products: Freebsd Freebsd.

## How do I fix CVE-2026-58083?

No fix has been published for CVE-2026-58083 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-58083 being exploited?

There is no known exploitation of CVE-2026-58083 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-2026-58083 and fix it if it is affected.

What it is: CVE-2026-58083 is a high-severity use after free vulnerability in Freebsd Freebsd, published on 19 Aug 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-2026-58083 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-2026-58083/ (Markdown: https://insights.sbomify.com/CVE-2026-58083/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-58083
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-58083
- OSV: https://osv.dev/vulnerability/CVE-2026-58083

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-58083/
Summaries are generated and may contain mistakes; the official description above is the record.