CVE-2026-58083: While the kernel was copying knotes during fork, a knote with a timer-based filter could fire and be enqueued

Routine

HIGH 8.4MITIGATE

CVE-2026-58083 is a high-severity flaw (CVSS 8.4) affecting freebsd. Below: why it ranks where it does, which versions are affected, what to do, and the exact commands.

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-a

Why this priority

High severity

No fix is published yet: follow the downgrade or mitigation steps.

Risk facts

CVSS score	8.4 (High)
Attack vector	Local
Attack complexity	Low
Privileges needed	None
User interaction	None
EPSS exploit chance	0.2% (top 94%)
CISA exploited list	No
Weakness	CWE-416
Published	2026-08-19
Last modified	2026-08-31

Publisher (CNA): FreeBSD · Vendor: freebsd

Last updated 2026-08-31 · Sources: CVE Program, NVD, CISA KEV, EPSS and vendor advisories · How we score

Am I affected?

Timeline

2026-08-19 08:17 UTCPublished CVE record published
2026-08-31 19:02 UTCUpdated Record last modified

freebsd freebsd MITIGATE

Affected: 15.1 · 15.1 p1 · 15.1 rc2 · 15.1 rc3-p1

Fixed in: no fixed release known

Safe to downgrade to: a release before 15.1

Check your OS release

cat /etc/os-release; uname -r

Debian / Ubuntu

sudo apt update && sudo apt full-upgrade

RHEL / Amazon Linux / Fedora

sudo dnf upgrade --refresh

Windows

Install the latest cumulative update from Windows Update

If no patch exists yet

OS downgrades are not safe. Apply the vendor mitigation from the advisory and restrict exposure.

Verify at the official source NVD · CVE Program · Report a problem with this page
Scores and fixes here are computed automatically from those and other public sources. Confirm with the vendor advisory before changing production systems.

Quick answers

How do I fix CVE-2026-58083?

freebsd: mitigate or apply the listed mitigation. Exact commands for each OS are on this page.

Is CVE-2026-58083 being exploited?

CVE-2026-58083 is not on the CISA Known Exploited Vulnerabilities list at the time of the last update. Check again, as this can change.

What does CVE-2026-58083 affect?

CVE-2026-58083 affects freebsd. Severity is high (CVSS 8.4). 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 kno

How urgent is CVE-2026-58083?

Priority 31/100. High severity

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References

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