FreeBSD kqueue knote race leads to privilege escalation
CVE-2026-58099 Published on October 15, 2026
Memory safety bugs in kqueue copy-on-fork implementation
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.
Vulnerability Analysis
CVE-2026-58099 can be exploited with local system access, and requires small amount of user privileges. This vulnerability is consided to have a high level of attack complexity. The potential impact of an exploit of this vulnerability is considered to be very high.
Weakness Types
What is a Race Condition Vulnerability?
The program contains a code sequence that can run concurrently with other code, and the code sequence requires temporary, exclusive access to a shared resource, but a timing window exists in which the shared resource can be modified by another code sequence that is operating concurrently.
CVE-2026-58099 has been classified to as a Race Condition vulnerability or weakness.
What is a Dangling pointer Vulnerability?
Referencing memory after it has been freed can cause a program to crash, use unexpected values, or execute code.
CVE-2026-58099 has been classified to as a Dangling pointer vulnerability or weakness.
Products Associated with CVE-2026-58099
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Affected Versions
FreeBSD:- Version 15.1-RELEASE and below p4 is affected.
Exploit Probability
EPSS (Exploit Prediction Scoring System) scores estimate the probability that a vulnerability will be exploited in the wild within the next 30 days. The percentile shows you how this score compares to all other vulnerabilities.