CVE-2021-45971 in InsydeH2O
Summary
by MITRE • 01/06/2022
An issue was discovered in SdHostDriver in Insyde InsydeH2O with kernel 5.1 before 05.16.25, 5.2 before 05.26.25, 5.3 before 05.35.25, 5.4 before 05.43.25, and 5.5 before 05.51.25. A vulnerability exists in the SMM (System Management Mode) branch that registers a SWSMI handler that does not sufficiently check or validate the allocated buffer pointer (CommBufferData).
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Analysis
by VulDB Data Team • 11/04/2025
The vulnerability identified as CVE-2021-45971 resides within the SdHostDriver component of Insyde InsydeH2O firmware implementations, specifically affecting kernel versions prior to designated patch levels across multiple kernel branches. This issue manifests in the System Management Mode (SMM) execution context where a software SMI (System Management Interrupt) handler is registered without adequate validation of the communication buffer pointer. The flaw represents a critical security gap in firmware-level operations that can potentially compromise system integrity and confidentiality. The vulnerability is particularly concerning because it operates within the SMM, which executes with the highest privilege level and operates outside the normal operating system execution context, making it difficult to detect and mitigate through conventional operating system security measures.
The technical implementation flaw stems from insufficient input validation within the SMM handler registration process for the SdHostDriver component. When a software SMI is triggered, the system invokes the registered SWSMI handler routine that processes communication data through the CommBufferData pointer. However, the handler does not perform adequate checks to validate the buffer pointer's legitimacy, memory allocation status, or access permissions before proceeding with data processing. This lack of validation creates a potential for arbitrary code execution or data corruption scenarios where malicious actors could manipulate the buffer pointer to redirect execution flow or inject malicious payloads. The vulnerability aligns with CWE-787 (Out-of-bounds Write) and CWE-121 (Stack-based Buffer Overflow) classifications, as the insufficient validation can lead to buffer overflows or memory corruption when processing unvalidated data pointers.
The operational impact of this vulnerability extends beyond typical software flaws due to its location within the SMM execution environment. Attackers who can trigger the SMI handler or manipulate the communication buffer data could potentially achieve privilege escalation to the highest system level, effectively bypassing all operating system security controls. This includes bypassing kernel protection mechanisms, memory protection, and user-mode access controls that normally prevent unauthorized system modifications. The vulnerability could enable persistent backdoor access, system state manipulation, or complete system compromise. According to ATT&CK framework, this vulnerability maps to techniques such as T1068 (Local Privilege Escalation) and T1543 (Create or Modify System Process) as it allows attackers to gain elevated privileges and potentially modify system-level processes. The SMM environment's isolation from normal OS operations makes detection particularly challenging, as traditional security monitoring tools may not observe or log the activities occurring within this privileged execution context.
Mitigation strategies for CVE-2021-45971 must focus on firmware-level updates and system hardening measures. The primary recommendation involves applying the vendor-supplied firmware patches that address the insufficient buffer validation in the SMM handler registration process. System administrators should prioritize updating all affected InsydeH2O firmware implementations across all kernel versions mentioned in the vulnerability description. Additionally, implementing firmware integrity monitoring solutions can help detect unauthorized modifications to the SMM handlers or communication buffers. Organizations should consider enabling firmware security features such as Secure Boot and Platform Configuration Registers (PCRs) to ensure firmware integrity. Network-level monitoring should include detection of unusual SMI activity patterns, and system administrators should implement regular firmware vulnerability assessments. The vulnerability also highlights the importance of supply chain security, as firmware updates from trusted sources are critical for maintaining system security. Organizations should maintain updated inventories of all firmware components and implement patch management processes specifically designed for firmware-level vulnerabilities.