Shared Buffers Data Read (SBDR)

A locally authenticated low-privileged attacker may disclose sensitive stale data originating from shared processor transaction buffers. Exposure can cross relevant software trust boundaries when untrusted code has MMIO access, creating particular concern for virtualized systems that expose device MMIO to untrusted guests. The vulnerability primarily affects confidentiality; no direct availability impact is described. Depending on platform configuration and co-scheduling, SMT may increase the opportunity for cross-thread races and confused-deputy data leakage.

Restrict direct MMIO access by untrusted software, especially device assignment or equivalent MMIO exposure to untrusted virtual-machine guests. On processors reporting FB_CLEAR support, use the memory-operand form of VERW to clear fill buffers at appropriate trust-boundary transitions. For systems also affected by MDS or TAA, clear fill buffers before transitions to untrusted software. Where an untrusted guest can access MMIO and MDS/TAA are not applicable, clear fill buffers before VMENTER. Avoid co-scheduling different security domains on SMT sibling threads through core scheduling or equivalent isolation; disabling SMT may be appropriate where robust domain isolation cannot otherwise be assured.

Apply the current Intel microcode or platform firmware update for the affected processor, together with the corresponding operating-system and VMM updates that implement the required buffer-clearing mitigations. For Red Hat Enterprise Linux deployments, install the applicable vendor kernel or kernel-rt security update for the supported product stream and reboot so that the updated kernel and microcode mitigations take effect. Confirm mitigation status using processor capability reporting and OS vulnerability-status interfaces; package version comparison alone may be unreliable where fixes are backported.