CVE-2021-46772 in EPYC 7002 Processors
Summary
by MITRE • 08/13/2024
Insufficient input validation in the ABL may allow a privileged attacker with access to the BIOS menu or UEFI shell to tamper with the structure headers in SPI ROM causing an out of bounds memory read and write, potentially resulting in memory corruption or denial of service.
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Analysis
by VulDB Data Team • 11/06/2024
The vulnerability identified as CVE-2021-46772 represents a critical security flaw within the Advanced Boot Loader (ABL) component of certain embedded systems and server platforms. This issue stems from inadequate input validation mechanisms that fail to properly verify the integrity and structure of data being processed during the boot initialization phase. The vulnerability specifically affects systems where the ABL is responsible for managing firmware operations and boot sequence validation, creating a potential attack surface that could be exploited by malicious actors with elevated privileges.
The technical implementation of this flaw occurs when a privileged attacker gains access to either the BIOS menu or UEFI shell environment, which provides them with the necessary execution context to manipulate SPI ROM structure headers. The insufficient validation allows for malformed or tampered data structures to be processed without proper boundary checking, leading to out-of-bounds memory read and write operations. This memory corruption vulnerability arises from the ABL's failure to implement proper bounds checking mechanisms when parsing SPI flash memory structures, particularly during the boot process where firmware integrity is paramount.
The operational impact of this vulnerability extends beyond simple denial of service conditions, as the memory corruption could potentially be leveraged to execute arbitrary code or compromise the integrity of the entire boot process. Attackers could manipulate the ABL to bypass security measures, modify boot parameters, or even inject malicious firmware components that persist across system reboots. The vulnerability's exploitation requires privileged access to the BIOS interface, which limits its accessibility but does not eliminate the risk, particularly in environments where physical access controls are insufficient or where attackers may have already compromised other system components.
From a cybersecurity framework perspective, this vulnerability aligns with CWE-129, which addresses insufficient input validation, and represents a classic example of how inadequate bounds checking can lead to memory corruption vulnerabilities. The attack pattern follows principles outlined in the ATT&CK framework under the boot or post-boot execution techniques, specifically targeting the firmware layer to establish persistent footholds within the system. Organizations should implement comprehensive firmware integrity monitoring solutions and ensure that physical access controls are maintained to prevent unauthorized manipulation of boot components.
Mitigation strategies for CVE-2021-46772 should focus on strengthening input validation mechanisms within the ABL implementation and implementing robust bounds checking for all SPI ROM structure parsing operations. System administrators should ensure that firmware updates are applied promptly to address the vulnerability, while also implementing strict access controls for BIOS and UEFI shell environments. Additional protective measures include enabling secure boot features, implementing firmware integrity verification mechanisms, and establishing monitoring protocols to detect unauthorized modifications to boot components. The vulnerability underscores the importance of maintaining proper security controls at all levels of the system architecture, particularly within the firmware and boot layers where traditional security measures may be insufficient.