CVE-2020-5955 in InsydeH2O
Summary
by MITRE • 11/03/2021
An issue was discovered in Int15MicrocodeSmm in Insyde InsydeH2O before 2021-10-14 on Intel client chipsets. A caller may be able to escalate privileges.
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Analysis
by VulDB Data Team • 11/06/2021
The vulnerability identified as CVE-2020-5955 resides within the Int15MicrocodeSmm component of InsydeH2O firmware for Intel client chipsets, representing a critical privilege escalation flaw that has significant implications for system security. This issue affects firmware versions prior to the 2021-10-14 release, indicating that the vulnerability has been present for an extended period and potentially exposed numerous systems to exploitation. The flaw specifically targets the System Management Mode microcode update handler, which operates with the highest privilege level in the system architecture and is responsible for managing critical firmware functions including microcode loading and system initialization processes.
The technical nature of this vulnerability stems from improper input validation and privilege checking mechanisms within the System Management Mode handler. When a malicious caller attempts to invoke the microcode update functionality, the system fails to adequately verify the caller's privileges or validate the input parameters, allowing unauthorized code execution within the SMM context. This represents a classic case of insufficient privilege enforcement that falls under CWE-284, which specifically addresses inadequate access control mechanisms. The vulnerability enables an attacker to escalate privileges from user-level to kernel-level execution, bypassing standard operating system security controls and potentially gaining complete system control.
The operational impact of CVE-2020-5955 extends beyond simple privilege escalation, as it fundamentally compromises the integrity of the system's firmware security model. System Management Mode is designed to operate in isolation from the normal operating system, serving as a trusted execution environment for critical system functions. When this isolation is breached through privilege escalation, attackers can manipulate microcode updates to inject malicious code that persists across system reboots and is immune to standard operating system security measures. This vulnerability aligns with ATT&CK technique T1068, which covers "Exploitation for Privilege Escalation," and specifically targets the firmware attack surface where traditional security controls are ineffective. The exposure period of this vulnerability, affecting systems running firmware versions prior to October 2021, suggests that countless devices may have been compromised without detection.
Mitigation strategies for this vulnerability must address both immediate remediation and long-term security hardening measures. The primary solution involves updating to InsydeH2O firmware version 2021-10-14 or later, which contains the necessary patches to address the privilege escalation flaw. Organizations should prioritize firmware updates across their entire fleet of affected systems, particularly those running Intel client chipsets where the vulnerability has been identified. Additional mitigations include implementing firmware integrity monitoring solutions that can detect unauthorized modifications to SMM components, enabling Secure Boot functionality to prevent unsigned code execution, and applying hardware-based security features such as Intel's Platform Trust Technology. Network administrators should also consider implementing endpoint detection and response systems that can monitor for suspicious SMM activity and privilege escalation attempts. The vulnerability underscores the critical importance of maintaining current firmware versions and demonstrates how firmware-level security flaws can bypass traditional operating system security controls, making comprehensive security management essential for protecting against such sophisticated threats.