CVE-2023-48733 in Ubuntu EDK II
Summary
by MITRE • 02/15/2024
An insecure default to allow UEFI Shell in EDK2 was left enabled in Ubuntu's EDK2. This allows an OS-resident attacker to bypass Secure Boot.
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Analysis
by VulDB Data Team • 05/08/2025
The vulnerability identified as CVE-2023-48733 represents a critical security flaw within the Unified Extensible Firmware Interface implementation of the EDK2 firmware development kit used by Ubuntu systems. This issue stems from an insecure default configuration that leaves the UEFI Shell enabled within the firmware environment, creating a persistent attack vector that undermines the fundamental security posture of modern computing platforms. The UEFI Shell serves as a command-line interface within the firmware that provides low-level system access and can be leveraged to execute arbitrary code with elevated privileges, making it a highly coveted target for sophisticated attackers seeking to establish persistent footholds within secure computing environments.
The technical flaw manifests in the default firmware configuration where the UEFI Shell remains enabled even when it should be disabled for security purposes. This misconfiguration allows an attacker who has already gained OS-level access to potentially exploit the firmware interface and bypass the Secure Boot mechanism that is designed to prevent unauthorized code execution during the system boot process. The vulnerability specifically affects Ubuntu systems that utilize EDK2 firmware components, where the default settings fail to properly restrict access to the UEFI Shell functionality. This creates a scenario where an attacker with minimal privileges on the operating system can escalate their privileges and gain access to firmware-level operations that should remain restricted.
The operational impact of this vulnerability extends far beyond simple privilege escalation, as it fundamentally undermines the security model of modern secure boot implementations. An attacker who successfully exploits this vulnerability can bypass hardware-level security controls that are designed to ensure only authenticated and trusted code executes during the boot process. This capability allows for the execution of malicious firmware components, potentially enabling rootkit installations that persist across operating system reboots and can evade traditional endpoint protection mechanisms. The attack surface is particularly concerning because it operates at a level below the operating system, making detection and remediation significantly more challenging. This vulnerability aligns with CWE-693, which addresses protection mechanism failures, and represents a critical weakness in the firmware security architecture that can be exploited using techniques described in the ATT&CK framework under the T1012 and T1068 tactics for privilege escalation and persistence.
Mitigation strategies for CVE-2023-48733 require immediate configuration updates to disable the UEFI Shell functionality within the firmware environment. System administrators should ensure that firmware updates are applied from Ubuntu's security repositories to address the specific default configuration issue. The recommended approach involves disabling the UEFI Shell through firmware configuration settings or by implementing firmware lockdown mechanisms that prevent unauthorized access to the UEFI interface. Additionally, organizations should conduct comprehensive firmware security audits to identify any other insecure default configurations that may exist within their EDK2 implementations. Regular monitoring of firmware versions and security patches, combined with proper access controls for firmware interfaces, will help prevent exploitation of similar vulnerabilities. The mitigation process should also include implementing firmware integrity checks and establishing secure boot policies that align with industry standards such as those defined by the UEFI Forum and the Trusted Computing Group to ensure comprehensive protection against firmware-level attacks.