CVE-2026-58100 FreeBSD CVE debrief

Who should care

FreeBSD system administrators and security teams should assess exposure and prioritize verification of systems with unprivileged local users. This vulnerability could allow an unprivileged local user to potentially escalate privileges, making it critical for those responsible for FreeBSD systems to evaluate their exposure and take necessary precautions.

Why it matters

CVE-2026-58100 is an out-of-bounds read vulnerability in the kqueue_fork_copy_knote() function that could allow an unprivileged local user to potentially escalate privileges on FreeBSD systems. System administrators and security teams should assess exposure and prioritize verification of systems with unprivileged local users.

• Potential privilege escalation by unprivileged local users
• Need to verify affected versions and vendor remediation
• Monitor system logs for potential exploitation attempts
• Assess exposure of FreeBSD systems

Technical summary

The kqueue_fork_copy_knote() function does not perform bounds checking when indexing into the child's file descriptor table, potentially allowing an unprivileged local user to escalate privileges. This vulnerability arises from a race condition where a concurrent thread in the parent could grow the parent's table and register knotes with file descriptor numbers beyond the end of the child's table. The function fails to validate the file descriptor number against the bounds of the child's file descriptor table, leading to an out-of-bounds read.

Defensive priority

Assess exposure and prioritize verification of FreeBSD systems, especially those with unprivileged local users.

Recommended defensive actions

• Assess exposure of FreeBSD systems to this vulnerability
• Verify if unprivileged local users can exploit this vulnerability
• Monitor system logs for potential exploitation attempts
• Review compensating controls for exposed systems while remediation is scheduled and verified
• Check relevant monitoring, detection, and logs for exposed assets that need extra review
• Track exceptions, retest remediated assets, and close the item only after evidence is documented
• Plan vendor-supported updates or mitigations through normal change control where exposure is confirmed

Evidence notes

The CVE record and NVD entry provide details on the vulnerability, but vendor remediation and affected versions require further verification. The vulnerability was publicly disclosed on October 15, 2026, and there have been no reported exploits. FreeBSD system administrators and security teams should assess exposure and prioritize verification of systems with unprivileged local users. The CVE Program and NVD provide official records and assessments, but additional details may be needed for comprehensive risk management.

Sources and references

Methodology and review provenance

AI-assisted synthesis based on stored public vulnerability evidence. System validation, approval state, and publication status do not by themselves establish human review of this revision. PatchSiren helps prioritize defensive review and does not prove exposure or remediation on any system.