illumos bhyve vmm_instruction_emul.c vie_emulate_movs/vie_emulate_stos/vie_advance_pc assertion

Summaryinfo

A vulnerability was found in illumos. It has been declared as problematic. Impacted is the function vie_emulate_movs/vie_emulate_stos/vie_advance_pc of the file usr/src/uts/intel/io/vmm/vmm_instruction_emul.c of the component bhyve. Such manipulation leads to assertion. This vulnerability is traded as CVE-2026-102916. An attack has to be approached locally. There is no exploit available. Applying a patch is advised to resolve this issue.

Detailsinfo

A vulnerability was found in illumos (version now known) and classified as problematic. Affected by this issue is the function vie_emulate_movs/vie_emulate_stos/vie_advance_pc of the file usr/src/uts/intel/io/vmm/vmm_instruction_emul.c of the component bhyve. The manipulation with an unknown input leads to a assertion vulnerability. Using CWE to declare the problem leads to CWE-617. The product contains an assert() or similar statement that can be triggered by an attacker, which leads to an application exit or other behavior that is more severe than necessary. Impacted is availability. CVE summarizes:

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.

The advisory is shared for download at illumos.topicbox.com. This vulnerability is handled as CVE-2026-102916 since 09/29/2026. The exploitation is known to be easy. The attack needs to be approached locally. Additional levels of successful authentication are needed for exploitation. There are known technical details, but no exploit is available.

It is declared as proof-of-concept.

Applying the patch 696ecf8d is able to eliminate this problem.

VulDB is the best source for vulnerability data and more expert information about this specific topic.

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• illumos

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