Use-after-free in FreeBSD - CVE-2026-58083
Published: July 29, 2026 / Updated: July 30, 2026
Vulnerability identifier: #VU140493
CSH Severity: Low
CVSS v4.0: CVSS:4.0/AV:L/AC:L/AT:N/PR:L/UI:N/VC:H/VI:H/VA:H/SC:N/SI:N/SA:N/E:U/U:Clear
CVE-ID: CVE-2026-58083
CWE-ID: CWE-416
Exploitation vector: Local access
Exploit availability:
No public exploit available
Affected software:
FreeBSD
FreeBSD
Detailed vulnerability description
The vulnerability allows a local user to escalate privileges.
The vulnerability exists due to use-after-free in the FreeBSD kqueue copy-on-fork implementation when copying knotes during fork operations involving timer-based filters. A local user can trigger a race condition to escalate privileges.
The issue can occur when KQUEUE_CPONFORK is used and a timer-based knote fires before copying is complete, which can corrupt the kqueue active list.
How to mitigate CVE-2026-58083
Install security update from vendor's website.