CVE-2021-21571 in UEFI BIOS
Summary
by MITRE • 06/24/2021
Dell UEFI BIOS https stack leveraged by the Dell BIOSConnect feature and Dell HTTPS Boot feature contains an improper certificate validation vulnerability. A remote unauthenticated attacker may exploit this vulnerability using a person-in-the-middle attack which may lead to a denial of service and payload tampering.
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Analysis
by VulDB Data Team • 07/02/2021
The vulnerability identified as CVE-2021-21571 resides within the Dell UEFI BIOS implementation and specifically affects the HTTPS stack utilized by two critical Dell features: BIOSConnect and HTTPS Boot. This weakness represents a significant security flaw in the firmware layer that governs the initial system boot process and network communications. The improper certificate validation mechanism creates a pathway for malicious actors to manipulate the secure boot process without requiring authentication or physical access to the target system. The vulnerability impacts Dell systems that utilize UEFI firmware with these specific features enabled, potentially affecting thousands of enterprise and consumer devices across multiple product lines including laptops, desktops, and servers.
The technical flaw manifests in the certificate validation process where the UEFI firmware fails to properly verify the authenticity and integrity of SSL/TLS certificates presented during HTTPS communications. This weakness allows attackers to perform man-in-the-middle attacks by presenting forged certificates that the system accepts as legitimate. The vulnerability stems from inadequate certificate chain validation and trust verification mechanisms within the UEFI HTTPS stack implementation. According to CWE classification, this maps to CWE-295 which specifically addresses "Improper Certificate Validation" in security protocols, making it a direct violation of secure communication standards. The flaw exists at the firmware level where cryptographic validation should occur before establishing secure connections for firmware updates or network boot operations.
The operational impact of this vulnerability extends beyond simple denial of service conditions to encompass potential payload tampering and complete system compromise. An attacker exploiting this vulnerability could intercept and modify firmware update packages, potentially installing malicious code that persists through system reboots and operating system installations. The remote nature of the attack means that adversaries can target systems from anywhere on the network without requiring physical access or authentication credentials. This vulnerability particularly affects the BIOSConnect feature which enables remote firmware management and the HTTPS Boot feature that allows systems to boot from network locations, both of which are commonly used in enterprise environments for system management and deployment. The attack vector aligns with ATT&CK technique T1542.001 for "Pre-OS Boot" and T1059.001 for "Command and Scripting Interpreter" when considering the potential for malicious payload execution.
Mitigation strategies for CVE-2021-21571 require immediate attention from system administrators and security teams responsible for Dell infrastructure. The primary recommendation involves updating the UEFI firmware to versions that address the certificate validation weakness, which Dell has released through their official support channels. Organizations should also implement network monitoring to detect unusual HTTPS traffic patterns that might indicate man-in-the-middle activity targeting these vulnerable systems. Security teams should consider disabling the affected BIOSConnect and HTTPS Boot features when not actively required for system management operations. Network segmentation and firewall rules can help limit exposure by restricting access to systems with these features enabled. The vulnerability demonstrates the critical importance of firmware security and highlights the need for robust certificate validation mechanisms in embedded systems. According to industry best practices and NIST guidelines, organizations should maintain updated firmware inventories and implement continuous monitoring for similar vulnerabilities in the UEFI layer. Regular security assessments of firmware components should be conducted to identify and remediate similar weaknesses that could compromise system integrity and security postures.