CVE-2020-5956 in InsydeH2O
Summary
by MITRE • 01/06/2022
An issue was discovered in SdLegacySmm in Insyde InsydeH2O with kernel 5.1 before 05.15.11, 5.2 before 05.25.11, 5.3 before 05.34.11, and 5.4 before 05.42.11. The software SMI handler allows untrusted external input because it does not verify CommBuffer.
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Analysis
by VulDB Data Team • 01/09/2022
The vulnerability identified as CVE-2020-5956 resides within the SdLegacySmm component of Insyde InsydeH2O firmware implementations across multiple kernel versions. This represents a critical security flaw that affects the System Management Mode SMI (System Management Interrupt) handler mechanism, which operates at a privileged level below operating system control and is responsible for handling system management interrupts that occur during normal operation. The vulnerability stems from insufficient input validation within the SMI handler implementation where CommBuffer parameters are not properly verified before processing, creating an avenue for exploitation that can bypass normal security boundaries.
This weakness manifests as a lack of proper authentication and validation mechanisms for external inputs entering through the SMI handler interface, allowing malicious actors to inject untrusted data into the system management mode execution context. The vulnerability is classified under CWE-20, "Improper Input Validation," which directly relates to the failure to validate external inputs before processing them within a system that operates at a higher privilege level. The SMI handler's failure to verify CommBuffer contents creates a potential attack surface where untrusted input can be manipulated to execute arbitrary code within the system management mode, which operates with elevated privileges and can bypass standard operating system security controls.
The operational impact of this vulnerability extends beyond typical software security concerns due to the privileged nature of SMI handlers and their role in system management operations. When exploited, this vulnerability allows attackers to potentially gain persistent access to system management mode, which can enable malicious actors to modify system firmware, intercept system calls, manipulate hardware components, or establish backdoors that persist across system reboots. The vulnerability affects multiple kernel versions, indicating it is a widespread issue within the InsydeH2O firmware implementation, and the specific version ranges suggest that vendors have released patches to address the issue. The security implications are particularly severe because SMI handlers operate outside the normal operating system execution context and can interact directly with hardware components, making them attractive targets for advanced persistent threats and rootkit development.
Mitigation strategies for this vulnerability require immediate firmware updates from affected vendors, as the patch versions mentioned in the CVE description (05.15.11, 05.25.11, 05.34.11, and 05.42.11) represent the first available fixes for this specific flaw. Organizations should also implement firmware integrity monitoring solutions to detect unauthorized modifications to system management mode components and establish robust supply chain security measures to prevent malicious firmware updates. From an ATT&CK framework perspective, this vulnerability maps to techniques involving system firmware modification and privilege escalation, specifically T1542.001 for System Firmware and T1068 for Exploitation for Privilege Escalation. The vulnerability also aligns with the broader category of hardware-based attack vectors that leverage firmware security weaknesses to establish persistent access to target systems, making it a significant concern for enterprise security teams and organizations implementing zero-trust security models that require verification of all system components.