CVE-2020-12944 in EPYC
Summary
by MITRE • 11/17/2021
Insufficient validation of BIOS image length by PSP Firmware could lead to arbitrary code execution.
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Analysis
by VulDB Data Team • 11/19/2021
The vulnerability identified as CVE-2020-12944 represents a critical flaw in the Platform Security Processor firmware implementation that affects systems utilizing AMD's Secure Processor. This issue stems from inadequate validation mechanisms within the PSP firmware's handling of BIOS image data, creating a potential pathway for malicious actors to execute arbitrary code on affected systems. The vulnerability specifically targets the firmware update process where the PSP fails to properly validate the length of incoming BIOS images, allowing for buffer overflow conditions that can be exploited to gain unauthorized system control.
The technical nature of this vulnerability resides in the insufficient input validation practices within the PSP firmware component, which operates as a dedicated security processor responsible for system boot integrity and secure operations. When a BIOS update is initiated, the PSP firmware should validate the image size against predetermined parameters to prevent maliciously crafted firmware updates from being processed. However, the flawed implementation allows attackers to craft BIOS images with invalid lengths that bypass these safety checks, potentially leading to memory corruption and execution of malicious code. This weakness aligns with CWE-129, which addresses insufficient validation of length of input buffers, and represents a classic buffer overflow vulnerability that can be leveraged for privilege escalation attacks.
The operational impact of CVE-2020-12944 extends beyond simple code execution capabilities, as it provides attackers with a potential foothold for more sophisticated attacks within the system's boot process. Since the PSP firmware operates at a low system level and controls critical security functions including secure boot validation, successful exploitation could enable attackers to bypass hardware-based security measures and potentially install rootkits or other persistent malware. The vulnerability is particularly concerning because it operates at the firmware level, making it difficult to detect and remediate through traditional software-based security measures. This aligns with ATT&CK technique T1068 which covers local privilege escalation and T1542 which addresses exploitation for privilege escalation through boot or logon initialization scripts.
Mitigation strategies for this vulnerability should focus on firmware updates from AMD and system vendors, as the primary fix requires addressing the validation logic within the PSP firmware itself. Organizations should prioritize updating their systems to the latest firmware versions provided by their hardware vendors, as these updates contain the necessary patches to correct the insufficient validation mechanisms. Additionally, system administrators should implement strict firmware update policies and ensure that only authenticated and verified firmware images are deployed to systems. Monitoring for unusual boot behavior or unexpected firmware modifications can also help detect potential exploitation attempts, though the low-level nature of the vulnerability makes detection particularly challenging. The remediation process should include verification that firmware updates have been properly applied and that system integrity checks are functioning correctly, as the vulnerability could potentially allow attackers to modify system security parameters in ways that are difficult to detect through standard security monitoring tools.