What’s Vulnerable › Vulnerabilities

CVE-2026-102916: Reachable assertion in illumos bhyve REP string instruction emulation allows guest to panic host

• Severity: medium (CVSS 6.8 v4.0)
• Exploited in the wild: not listed in CISA KEV
• EPSS: 0.1% probability of exploitation in the next 30 days
• Public exploit or detection template: none known
• Published: 2026-10-09 · updated 2026-10-09
• Weakness: CWE-617

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

• illumos-gate: all versions
• OmniOS: from any before r151054; from r151058 before r151058w; from r151056 before r151056aw; from r151054 before r151054bw — fixed in r151054, r151054bw, r151056aw, r151058w

How to fix

Upgrade to a fixed version: OmniOS r151054, r151054bw, r151056aw, r151058w. Check the vendor advisory for mitigations.

References

• https://github.com/illumos/illumos-gate/commit/696ecf8debceed9dc33937d8c8e111e4aeebfdae
• https://illumos.org/issues/18491
• https://illumos.topicbox.com/groups/developer/T697a32b688807e56/cve-2026-102916-18491-bhyve-rep-prefix-instr-emulation-fumbles-flags
• http://www.openwall.com/lists/oss-security/2026/10/09/19

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