CVE-2026-58083

Kernel use-after-free via forked knote race

Published Aug 19, 2026 · Updated Aug 20, 2026

Use-after-free in kqueue copy-on-fork in FreeBSD before 15.1-RELEASE-p2 allows local users to gain privileges via a fork race. In sys/kern/kern_event.c, kqueue_fork_copy_knote() copied knote state without holding the kqueue and knlist locks, then evaluated and enqueued the child timer knote after state had changed, so the same copied knote could be linked onto the active list twice. Reachability requires local code execution on a system that uses KQUEUE_CPONFORK; once triggered, the corrupted active list can free a knote that the kernel still references, which FreeBSD reports as a path to privilege escalation.

CVSS severity8.4
High
EPSS probability0.12%
Next 30 days · Sep 16, 2026
Known exploitationUnconfirmed
Based on sourced intelligence
Hinoki checkNot available
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Summary

What happened

Use-after-free in kqueue copy-on-fork in FreeBSD before 15.1-RELEASE-p2 allows local users to gain privileges via a fork race. In sys/kern/kern_event.c, kqueue_fork_copy_knote() copied knote state without holding the kqueue and knlist locks, then evaluated and enqueued the child timer knote after state had changed, so the same copied knote could be linked onto the active list twice. Reachability requires local code execution on a system that uses KQUEUE_CPONFORK; once triggered, the corrupted active list can free a knote that the kernel still references, which FreeBSD reports as a path to privilege escalation.

The record

CVE
CVE-2026-58083
Published
Aug 19, 2026
Updated
Aug 20, 2026
Vendor
The FreeBSD Project
Product
FreeBSD
Classifications
CWE-416, T1068
Attack vector
local
Privileges
authenticated

Timeline

How it unfolded

  1. Aug 19, 2026CVE publishedPublication date reported by the CVE source.
  2. Aug 20, 2026Record updatedLatest update available in the CVE record.

Exploitability

Present is not the same as exploitable

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Is a vulnerable build present?

Compare these published version ranges with your installed build and any vendor patches.

  1. Affected versionversion=15.1-RELEASE <p2

What conditions does exploitation require?

Attack vectorlocal
Required privilegesauthenticated

What is affected?

The FreeBSD Project · FreeBSDversion=15.1-RELEASE <p2

Published CVSS scores

8.4CISA-ADPCVSS:3.1/AV:L/AC:L/PR:N/UI:N/S:U/C:H/I:H/A:H

CVSS describes severity. EPSS estimates exploitation probability.

Attacks

What attackers are doing with it

Daily unique IPs observed by Shadowserver honeypots for known exploited vulnerabilities (KEVs). Missing observations do not establish an absence of attacks.

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No observations available

Sep 10, 2026Sep 16, 2026
Latest reporting daySep 16, 2026
Latest daily unique IPsUnavailable
Prior 30-day averageUnavailable
SourceShadowserver honeypots (KEV)
Vectorlocal
Privilegesauthenticated
Known exploitationUnconfirmed
Public exploitUnconfirmed

Weakness, pattern, technique

CWE-416Use After Free
T1068Exploitation for Privilege Escalation

Public exploit references

No public exploit references are available in this record.

Labels summarize the accepted research assessment. They do not indicate a test against your environment.

Technologies

Your stack

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Your stack

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