# CVE-2026-58099: Memory safety bugs in kqueue copy-on-fork implementation

> A race condition in FreeBSD's kqueue copy-on-fork implementation allows local attackers to trigger a use-after-free and escalate privileges.

- **Severity:** High 7.0 (`CVSS:3.1/AV:L/AC:H/PR:L/UI:N/S:U/C:H/I:H/A:H`)
- **Exploited in the wild:** Not known
- **Login needed:** Any signed-in user
- **Attackable:** Local or same network only
- **Victim action needed:** Not needed
- **Fix available:** No
- **Published:** 15 Oct 2026
- **Updated:** 19 Oct 2026
- **Also known as:** GHSA-f53j-rp59-76p7

## What is CVE-2026-58099?

CVE-2026-58099 is a high-severity use after free vulnerability in Freebsd Freebsd, published on 15 Oct 2026. It can only be exploited from the same machine or local network, with no action from the victim.

### Official description

When copying knotes from a parent kqueue to a child, the copy code did not correctly exclude marker knotes (used internally to track list traversal position) before marking them as in-flux and releasing the kqueue lock.  If another thread freed a marker while the lock was dropped, the subsequent in-flux decrement operated on freed memory.

An unprivileged local user may be able to exploit these races to escalate privileges.

Weakness: CWE-416 (Use After Free), CWE-362 (Concurrent Execution using Shared Resource with Improper Synchronization)

## Which versions are affected by CVE-2026-58099?

It affects 1 product.


Products: Freebsd Freebsd.

## How do I fix CVE-2026-58099?

No fix has been published for CVE-2026-58099 yet. Limit exposure of the affected software until one is available.

## Is CVE-2026-58099 being exploited?

There is no known exploitation of CVE-2026-58099 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-2026-58099 and fix it if it is affected.

What it is: CVE-2026-58099 is a high-severity use after free vulnerability in Freebsd Freebsd, published on 15 Oct 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-2026-58099 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-2026-58099/ (Markdown: https://insights.sbomify.com/CVE-2026-58099/index.md)
```

## Sources

- CVE record: https://www.cve.org/CVERecord?id=CVE-2026-58099
- NVD: https://nvd.nist.gov/vuln/detail/CVE-2026-58099
- OSV: https://osv.dev/vulnerability/CVE-2026-58099

---
From sbomify Insights: https://insights.sbomify.com/CVE-2026-58099/
Summaries are generated and may contain mistakes; the official description above is the record.