EUVD-2026-66253Severity by source
AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H
Local ioctl exploitation requires PR:L (unprivileged local user); race is reliably triggerable justifying AC:L; full C/I/A reflects complete privilege escalation to root.
Primary rating from Vendor (freebsd).
CVSS VectorVendor: freebsd
Lifecycle Timeline
4DescriptionCVE.org
The FIOSSHMLPGCNF ioctl(2) operation configures the page size for a largepage shared memory object. This is intended to be used immediately after creating the object, before any memory is allocated for the object. The handler checked whether a page size had already been configured without holding the rangelock. Two concurrent callers could both observe an unconfigured object and set conflicting page sizes, leaving the object in an inconsistent state.
An unprivileged local user can exploit this race to escalate privileges.
AnalysisAI
Privilege escalation in FreeBSD's POSIX shared memory subsystem allows an unprivileged local user to gain root-level access by exploiting a race condition in the FIOSSHMLPGCNF ioctl handler. The kernel's largepage shared memory page-size configuration check is performed without holding the rangelock, enabling two concurrent callers to each observe an unconfigured object and write conflicting page sizes, corrupting kernel object state in an exploitable way. …
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Attack ChainAIDerived
Hypothetical attack flow derived from CVE metadata
Vulnerability AssessmentAI
| Exploitation | Exploitation requires a local unprivileged user account on a vulnerable FreeBSD system, confirmed by CVSS PR:L and the vendor description explicitly stating 'an unprivileged local user can exploit this race.' The attacker must be able to create POSIX shared memory objects (shm_open(2)) - a capability available to all unprivileged users by default on FreeBSD - and must invoke the FIOSSHMLPGCNF ioctl concurrently from two threads or processes against the same object before any backing memory has been allocated. … Additional conditions and limiting factors are described in the full assessment. |
| Risk Assessment | The CVSS 7.8 vector (AV:L/AC:L/PR:L/UI:N/S:U/C:H/I:H/A:H) accurately captures the threat model: any unprivileged local user with shell access can attempt exploitation with no required user interaction and no elevated starting privileges. … Full risk analysis with EPSS, KEV, and SSVC signal comparison available after sign-in. |
| Exploit Scenario | Full exploit scenario with step-by-step reproduction available after sign-in. |
| Remediation | The primary fix is to update to a patched release: FreeBSD 14.4-RELEASE-p9, FreeBSD 15.0-RELEASE-p13, or FreeBSD 15.1-RELEASE-p3, as documented in FreeBSD Security Advisory FreeBSD-SA-26:63.posixshm.asc at https://security.freebsd.org/advisories/FreeBSD-SA-26:63.posixshm.asc. … Detailed patch versions, workarounds, and compensating controls in full report. |
Recommended ActionAI
Within 24 hours: Inventory all FreeBSD deployments (versions, deployment types-bare metal, containers, virtual machines) and document which systems have unprivileged local users or multi-tenant access. …
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External POC / Exploit Code
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