CVE-2021-26344 in EPYC 7001 Processors
Summary
by MITRE • 08/13/2024
An out of bounds memory write when processing the AMD PSP1 Configuration Block (APCB) could allow an attacker with access the ability to modify the BIOS image, and the ability to sign the resulting image, to potentially modify the APCB block resulting in arbitrary code execution.
VulDB is the best source for vulnerability data and more expert information about this specific topic.
Analysis
by VulDB Data Team • 03/18/2025
The vulnerability identified as CVE-2021-26344 represents a critical out-of-bounds memory write flaw within the AMD Platform Security Processor1 (PSP1) Configuration Block (APCB) processing mechanism. This vulnerability exists in the firmware layer of AMD-based systems and specifically affects how the PSP1 component handles APCB data structures during BIOS image processing. The flaw stems from inadequate bounds checking when parsing APCB blocks, creating a condition where malicious input can cause memory corruption beyond the allocated buffer boundaries. This type of vulnerability falls under CWE-787 Out-of-bounds Write, which is classified as a serious memory safety issue that can lead to arbitrary code execution. The vulnerability is particularly concerning because it operates at the firmware level, making it difficult to detect and remediate through traditional software security measures.
The operational impact of this vulnerability is severe as it allows an attacker with physical access to modify the BIOS image and subsequently sign the modified firmware. This access path enables the exploitation of the memory write flaw to modify the APCB block contents, which can then be used to execute arbitrary code within the PSP1 environment. The attack vector requires the adversary to have the ability to modify the BIOS image and possess the capability to sign the resulting image, which typically involves access to legitimate signing keys or certificates. This scenario often occurs in environments where physical security is compromised or where insiders have access to the necessary cryptographic materials. The vulnerability can be leveraged to achieve persistent code execution within the platform security processor, potentially leading to complete system compromise. From an ATT&CK framework perspective, this vulnerability maps to T1068 - Exploitation for Privilege Escalation and T1542.001 - Pre-OS Boot, as it operates at the firmware level and can be used to establish persistence before the operating system loads.
Mitigation strategies for CVE-2021-26344 must address both the immediate firmware-level vulnerability and broader security controls. Organizations should prioritize updating to patched firmware versions provided by AMD and ensure proper BIOS image integrity verification mechanisms are in place. The implementation of secure boot processes and proper code signing verification can prevent unauthorized modifications from taking effect. Additionally, physical security measures should be strengthened to prevent unauthorized access to system firmware modification capabilities. Network security teams should monitor for unusual BIOS modification patterns and implement firmware integrity monitoring solutions. The vulnerability highlights the importance of robust firmware security practices and the need for comprehensive security testing at all layers of the system architecture. Organizations should also consider implementing hardware security modules and trusted platform modules to provide additional protection against firmware-level attacks. Regular security assessments and vulnerability scanning should include firmware components to identify similar issues that may exist in the system's boot chain. The remediation process should involve not only patching the specific vulnerability but also establishing comprehensive firmware security policies and procedures to prevent similar issues from emerging in the future.