# CVE-2026-58098: FreeBSD kernel heap out-of-bounds access in semop(2)

Source: https://junglewise.ai/threats/cve-2026-58098-when-semop-2-blocks-waiting-for-a-semaphore-condition-it-releases  
Publisher: Junglewise Threat Intelligence, https://junglewise.ai/threats  
Published: 2026-10-15. Updated: 2026-10-16  
License: CC BY 4.0 with a link back

CVE-2026-58098 · Severity: high · CVSS 8.4 · Published 2026-10-15

FreeBSD's semop system call, which manages inter-process synchronization using semaphore sets, contains a flaw in its sequence number validation logic. An unprivileged local attacker can exploit a counter wraparound to trick the kernel into accessing invalid memory on the heap, potentially achieving privilege escalation.

Technologies: [Freebsd](https://junglewise.ai/threats/technologies/freebsd). Vendors: [Freebsd](https://junglewise.ai/threats/vendors/freebsd).

## Quick answers

**Is CVE-2026-58098 exploited in the wild?** No. Junglewise Threat Intelligence has no report of CVE-2026-58098 being exploited in the wild.

**How severe is CVE-2026-58098?** High severity, with a CVSS score of 8.4, published 15 October 2026.

**Which products and versions are affected?** Freebsd All supported versions prior to the correction dates.

**Is there a fix for CVE-2026-58098?** Yes: fixed in FreeBSD 15.1-RELEASE-p4, 15.0-RELEASE-p14, 14.5-RELEASE-p1, 14.4-RELEASE-p10, stable/15, stable/14. Junglewise finds every place you run it, drafts the upgrade and applies it once you approve.

**How is CVE-2026-58098 attacked?** It is attacked with local access, in an operating system.

**Am I affected by CVE-2026-58098?** Check whether you run Freebsd at an affected version. Junglewise does that check for you around the clock: connect your code, cloud and domains, and it matches new vulnerabilities like this one against what you actually run and tells you when one reaches you.

## How to fix

- Fixed in FreeBSD 15.1-RELEASE-p4, 15.0-RELEASE-p14, 14.5-RELEASE-p1, 14.4-RELEASE-p10, stable/15, stable/14

## Technical details

When semop(2) wakes from blocking, it uses a 15-bit sequence number embedded in the IPC identifier to verify the semaphore set still exists. If enough sets are created and destroyed in the same slot while a caller is blocked, the counter wraps and semop may access freed or unrelated heap memory out of bounds. The vulnerability requires local access and involves a timing race condition, with successful exploitation potentially allowing privilege escalation.

## Affected products

- FreeBSD FreeBSD All supported versions prior to the correction dates

## Timeline

- 2026-09-29: disclosed: FreeBSD Security Advisory SA-26:64 published
- 2026-09-29: patched: Patches released for all supported branches

## References

- [https://security.freebsd.org/advisories/FreeBSD-SA-26:64.sysvsem.asc](https://security.freebsd.org/advisories/FreeBSD-SA-26:64.sysvsem.asc)

## Related threats

- [FreeBSD kqueue out-of-bounds read in fork copy](https://junglewise.ai/threats/cve-2026-58100-kqueue-fork-copy-knote-indexed-into-the-child-s-file-descriptor)
- [FreeBSD kernel kqueue memory safety bugs in copy-on-fork](https://junglewise.ai/threats/cve-2026-58099-when-copying-knotes-from-a-parent-kqueue-to-a-child-the-copy-code)
- [FreeBSD sound(4) use-after-free in buffer resize TOCTOU race](https://junglewise.ai/threats/cve-2026-101308-when-an-audio-channel-s-buffer-needs-to-be-resized-the-sound-4)
- [FreeBSD RACK stack buffer overflow in tcp_rack](https://junglewise.ai/threats/cve-2026-101307-when-the-pcm-sample-array-needs-to-grow-the-rack-stack-doubles-a)
- [FreeBSD jail filesystem root escape via SCM_RIGHTS](https://junglewise.ai/threats/cve-2026-101306-scm-rights-file-descriptor-passing-did-not-preserve-fd-resolve)