CVE-2021-26316 in AMD
Summary
by MITRE • 01/11/2023
Failure to validate the communication buffer and communication service in the BIOS may allow an attacker to tamper with the buffer resulting in potential SMM (System Management Mode) arbitrary code execution.
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Analysis
by VulDB Data Team • 04/09/2025
The vulnerability identified as CVE-2021-26316 represents a critical flaw in the BIOS implementation that undermines the security boundaries of system management mode. This issue stems from insufficient validation mechanisms within the communication buffer and service components that are essential for maintaining the integrity of the system's firmware layer. The failure to properly validate these communication pathways creates a potential attack surface that could be exploited by malicious actors seeking to compromise the foundational security architecture of computing systems.
The technical flaw manifests in the absence of proper buffer validation checks during communication between the BIOS and system management components. When communication buffers are not adequately validated, attackers can manipulate the data flow to inject malicious payloads that may execute arbitrary code within the System Management Mode context. This represents a severe escalation of privileges since SMM operates with the highest privilege level and is isolated from the operating system, making it an attractive target for attackers seeking persistent system compromise. The vulnerability specifically affects the communication service implementation where buffer boundaries are not properly enforced, allowing for potential buffer overflow conditions or data manipulation attacks.
The operational impact of CVE-2021-26316 extends beyond simple privilege escalation to encompass potential system compromise and persistent backdoor capabilities. Attackers who successfully exploit this vulnerability can gain unrestricted access to system management functions and potentially establish rootkit-like persistence within the firmware layer. This makes the vulnerability particularly dangerous as it operates below the operating system level and can evade traditional security monitoring mechanisms. The attack vector typically involves crafting malicious input that bypasses buffer validation checks, leading to code execution within SMM where the attacker can manipulate system behavior, access memory, or modify firmware components without detection.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-129, which addresses insufficient input validation, and maps to ATT&CK technique T1068, which covers local privilege escalation through system management mode manipulation. The weakness demonstrates the critical importance of firmware security validation and the need for comprehensive security testing of system management components. Organizations should prioritize immediate firmware updates from vendors, implement firmware integrity monitoring solutions, and conduct thorough security assessments of their system management modes. Additionally, the vulnerability highlights the necessity of maintaining up-to-date security patches and establishing robust firmware security practices that include proper buffer validation, input sanitization, and secure communication protocols within the BIOS layer.
This vulnerability type represents a fundamental flaw in the security architecture of modern computing systems where the assumption of trusted firmware components is violated. The lack of proper validation creates a pathway for attackers to establish persistent access to systems while operating outside the normal operating system security boundaries. The implications extend to enterprise environments where such vulnerabilities could enable attackers to maintain long-term access to critical infrastructure systems, making the remediation of this issue a high priority for security teams. The vulnerability also underscores the importance of supply chain security and the need for comprehensive firmware security testing throughout the development lifecycle to prevent similar issues from emerging in future system implementations.