Description

SMM IHISI command handler, FMTSWriteUseIntelLib, for FMTS command 0x32, read and write data without checking buffer size and could cause buffer overflow.

Executive Summary

Technical Details

Mitigations

References

Additional Metadata

{
  "score": "2.7",
  "pubDate": "2026-08-26T05:18:28.547Z",
  "pubdate": "2026-08-26T05:18:28.547Z",
  "executiveSummary": "A critical buffer overflow vulnerability exists within the System Management Mode (SMM) IHISI (Insyde H2O Insyde Software Interface) command handler, specifically within the FMTSWriteUseIntelLib function responsible for processing FMTS command 0x32.\nThe vulnerability is characterized by a lack of input validation regarding the size of the data being processed during read and write operations. This deficiency allows an attacker to trigger an out-of-bounds write condition within the SMM execution environment.\nThe impact of this flaw is severe, potentially enabling arbitrary code execution with the highest level of system privileges. Because SMM code runs with greater authority than the operating system kernel and hypervisor, successful exploitation grants an attacker full control over the platform, allowing for persistent firmware-level compromise and bypass of security features such as Secure Boot.\nExploitation requires an attacker to possess sufficient privileges to interface with the SMM handler from the OS level, typically via specialized drivers or direct communication with the IHISI interface. No network exposure is inherent to the vulnerability itself, but local exploitation provides a conduit for system-wide compromise.",
  "technicalDetails": "The vulnerability resides in the SMM IHISI interface, which acts as a communication bridge between the OS and the firmware. Specifically, the function FMTSWriteUseIntelLib, invoked by FMTS command 0x32, fails to perform rigorous bounds checking on the input buffer supplied by the caller.\nIn the context of the SMM IHISI command architecture, data is passed from the guest-level environment to the SMM-level via communication buffers. The FMTSWriteUseIntelLib function facilitates data manipulation; however, it neglects to validate that the size of the data provided in the communication buffer conforms to the expectations of the destination buffer size within the SMM memory space.\nThe exploitation flow initiates when a privileged attacker sends a malformed FMTS command (0x32) to the IHISI interface. The attacker defines the payload length and content within the communication buffer. When FMTSWriteUseIntelLib is triggered, it proceeds to copy or manipulate the data without verifying the size constraints. This behavior leads to a linear buffer overflow, overwriting adjacent memory locations within the SMRAM (System Management RAM).\nBecause the SMM environment operates with elevated privileges, memory corruption at this layer allows for the manipulation of function pointers, return addresses on the stack, or other critical structures within the firmware. By carefully crafting the overflow payload, an attacker can redirect the execution flow to malicious code embedded in the communication buffer, effectively achieving arbitrary code execution within the SMM context.\nSince SMM executes in a privileged mode hidden from the operating system, post-exploitation impact includes the ability to disable hardware-level security protections, hook SMI (System Management Interrupt) handlers, exfiltrate sensitive data (such as cryptographic keys), or deploy persistent firmware-based rootkits. The lack of size validation effectively bypasses any existing security mechanisms that might rely on the assumption of a static, controlled buffer size, rendering the interface inherently insecure against specifically crafted malicious input."
}