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8.4
CVE-2026-58083: FreeBSD kqueue copy-on-fork vulnerability allows local privilege escalation
CVE-2026-58083 · published 2 months ago
Summary
A bug in the FreeBSD kqueue feature allows an attacker with local access to potentially take control of the system. This vulnerability affects systems running FreeBSD and can be exploited by an attacker with local access. To protect your system, apply any available security patches and ensure your software is up-to-date.
What to do
- Update freebsd freebsd to version p2 or later.
Affected software
| Vendor | Product | Affected versions |
|---|---|---|
| freebsd | freebsd |
< p2 15.1 |
Original advisory text
Use-after-free in kqueue copy-on-fork
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.
An unprivileged local user can trigger a use-after-free in the kernel, potentially leading to privilege escalation.
References
Internet-facing
14 days
Internal
At next upgrade
- Not known to be exploited
- Needs hands-on effort to exploit
- Gives an attacker full control
Severity
8.4
High
Type
CWE-416Use After Free
Timeline
Published19 Aug 2026
Updated4 Nov 2026
First seen19 Aug 2026
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