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.
- Exploited in the wild
- Not known
- Login needed
- Any signed-in user
- Attackable
- Local or same network only
- Victim action needed
- Not needed
- Fix
- None listed
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.
Which versions are affected by CVE-2026-58099?
It affects 1 product.
Products include 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.
Upgrade to the fixed version. These bugs are found with fuzzing and sanitisers and avoided by memory-safe languages. More about Use after free.
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
Sources
Also known as GHSA-f53j-rp59-76p7.