CVE-2021-45969 in InsydeH2O
Summary
by MITRE • 01/06/2022
An issue was discovered in AhciBusDxe 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 (the CommBuffer+8 location).
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Analysis
by VulDB Data Team • 11/04/2025
The vulnerability identified as CVE-2021-45969 resides within the AhciBusDxe driver component of Insyde InsydeH2O firmware implementations, specifically affecting kernel versions prior to designated patch levels across multiple release branches. This flaw manifests in the System Management Mode (SMM) execution context where a Software SMI (SWSMI) handler is registered without adequate validation of the communication buffer pointer, creating a critical security gap that can be exploited by malicious actors with appropriate privileges.
The technical implementation of this vulnerability stems from insufficient input validation within the SMM handler registration process. When the SWSMI handler is established, the system fails to properly verify the CommBuffer+8 location pointer, which serves as the communication channel between the SMI handler and the calling entity. This pointer validation failure creates a potential buffer overflow or arbitrary code execution scenario, as an attacker can manipulate the buffer pointer to redirect execution flow or corrupt memory structures. The vulnerability directly corresponds to CWE-787: Out-of-bounds Write and CWE-122: Heap-based Buffer Overflow, both of which are classified as high-severity issues in the Common Weakness Enumeration catalog.
The operational impact of this vulnerability extends beyond traditional software exploitation vectors due to its SMM context. SMM operates with the highest privilege level on x86 systems, making any compromise of SMM handlers potentially catastrophic for system security. Attackers who can trigger the SWSMI handler through legitimate means or by exploiting other vulnerabilities could gain complete system control, including the ability to execute code with SMM privileges, modify system memory, and potentially persist across system reboots. This aligns with ATT&CK technique T1068: Exploitation for Privilege Escalation and T1543.003: Create or Modify System Process: Windows Service, as the vulnerability enables unauthorized privilege escalation and persistent access to the system's most critical execution environment.
Mitigation strategies for CVE-2021-45969 require immediate firmware updates from Insyde to patch the identified vulnerability in all affected kernel versions. Organizations should prioritize applying the vendor-supplied patches that address the insufficient buffer pointer validation in the SMM handler registration process. Additionally, system administrators should implement monitoring for unusual SMI activity and consider disabling unnecessary SMI handlers when possible. The remediation efforts must be comprehensive across all affected InsydeH2O implementations, ensuring that all kernel branches receive the appropriate security updates to prevent exploitation. Network segmentation and access controls should be maintained as defensive measures, while continuous firmware integrity monitoring should be implemented to detect any unauthorized modifications to system management components that could potentially re-introduce this vulnerability or similar flaws.