Description
A reachable assertion in the illumos bhyve instruction emulator allows a guest to panic the host. When emulating a REP-prefixed MOVS or STOS instruction that accesses guest MMIO, vie_emulate_movs() and vie_emulate_stos() in usr/src/uts/intel/io/vmm/vmm_instruction_emul.c do not clear the VIES_REPEAT status flag on the final iteration. For MMIO regions emulated in the kernel (the local APIC, I/O APIC and HPET), the stale flag causes a VERIFY assertion in vie_advance_pc() to fail, and the host panics. A privileged user within a guest VM can issue a REP MOVS or REP STOS instruction against the local APIC page to cause a denial of service of the host and every other guest running on it. The flaw has existed since 2020 (illumos-gate commit e0c0d44e), and affects any illumos distribution prior to illumos-gate commit 696ecf8d.
Affected products
Version statuses are supplied by the assigning organization. Consult the original record for detailed ranges and platform conditions.
illumos illumos-gate
Default version status: affected
e0c0d44e917080841514d0dd031a696c74e8c435 to < 696ecf8debceed9dc33937d8c8e111e4aeebfdaeaffected
OmniOS OmniOS
Default version status: affected
any to < r151054affectedr151058 to < r151058waffectedr151056 to < r151056awaffectedr151054 to < r151054bwaffected
References
- https://illumos.topicbox.com/groups/developer/T697a32b688807e56/cve-2026-102916-18491-bhyve-rep-prefix-instr-emulation-fumbles-flags ↗
- https://illumos.org/issues/18491 ↗
- https://github.com/illumos/illumos-gate/commit/696ecf8debceed9dc33937d8c8e111e4aeebfdae ↗
- http://www.openwall.com/lists/oss-security/2026/10/09/19 ↗