Insyde InsydeH2O (IdeBusDxe SMI input buffer, DMA TOCTOU): SMRAM corruption via a DMA race on the legacy IDE/ATA bus

Impact

SMRAM corruption via a DMA race on the legacy IDE/ATA bus driver. Worth noting for fleet operators that this driver is usually only live when CSM / legacy storage compatibility is enabled - so unlike most of this batch, there is a real chance the attack surface is simply not present on a modern UEFI-only server profile.

Who can reach it

An attacker able to drive DMA at host memory while the SMI handler is mid-flight - a malicious PCIe device, a peripheral running attacker-flashed firmware (NIC, GPU, NVMe), or a tenant with a passed-through device that is not behind a correctly configured IOMMU. Notably does NOT require host root, which is what separates this family from the ordinary SMM callout bugs.

What to do

Firmware flash from the server OEM, not from Insyde - the fixed Insyde kernel has to be rebased by Dell/HPE/Lenovo/Supermicro and re-qualified before it reaches you, which for this batch ran months behind Insyde's own release. One reboot per node, so schedule it against a GPU drain. Fixed in kernel 5.2 / 05.27.25, 5.3 / 05.36.25, 5.4 / 05.44.25. Genuine config lever on this one: disable CSM / legacy storage support in BIOS on UEFI-only nodes, which removes the driver rather than just patching it. The compensating control that actually works here is the IOMMU, and Insyde says so in the advisory: enable VT-d/AMD-Vi with pre-boot DMA protection so the ACPI runtime buffer the handler reads is not reachable by an untrusted device. That is a BIOS setting, deployable fleet-wide without a flash, and it should be on already on any node that passes devices through to tenants. Patch the batch, not the CVE - Insyde filed one advisory per driver for the same defect, so fixing this one leaves every sibling handler reachable.

References