CVE-2026-58098 FreeBSD CVE debrief

Who should care

FreeBSD system administrators and security teams should assess exposure, verify patching, and monitor system logs for unusual activity. They should also review compensating controls for exposed systems and track exceptions. Security teams should prioritize verifying patching and monitoring system logs.

Why it matters

CVE-2026-58098 is a vulnerability in the FreeBSD semop system call that can lead to out-of-bounds kernel heap access and potential privilege escalation. FreeBSD system administrators and security teams should assess exposure, verify patching, and monitor system logs for unusual activity.

• Potential privilege escalation via out-of-bounds kernel heap access
• Unprivileged local users can trigger the vulnerability
• Verification of FreeBSD system patching and log monitoring is required

Technical summary

The semop system call in FreeBSD releases the per-set lock and sleeps when blocking waiting for a semaphore condition. Upon waking, it checks the sequence number embedded in the semaphore set's IPC identifier to detect whether the set was removed while the caller was asleep. However, this sequence number is only 15 bits wide, which can lead to a wrap-around and cause semop to falsely conclude that the original set still exists. This can result in an out-of-bounds access on kernel heap memory.

Defensive priority

Verify and apply patches for FreeBSD systems; monitor system logs for unusual semop activity.

Recommended defensive actions

• Verify and apply patches for FreeBSD systems
• Monitor system logs for unusual semop activity
• Restrict access to semaphore sets
• Confirm whether affected product deployments exist in managed environments and assign an owner for follow-up.
• 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.

Evidence notes

The CVE record and NVD entry provide details on the vulnerability. Additional information is limited. The FreeBSD security advisory for CVE-2026-58098 provides further context. Evidence limits suggest verifying patching and monitoring system logs for unusual semop activity. Defensive verification tasks include reviewing system patching and log monitoring.

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.