CVE-2023-48733 is a vulnerability identified in the Ubuntu EDK II implementation maintained by Canonical Ltd. The issue stems from an insecure default configuration that leaves the UEFI Shell enabled within the EDK II firmware environment. EDK II is a widely used open-source implementation of the UEFI (Unified Extensible Firmware Interface) specification, which is critical for system boot processes. The UEFI Shell is a command-line environment that can be used to execute commands and scripts at the firmware level. By default, this shell should be disabled or properly secured to prevent unauthorized access. In this case, the insecure default allows an attacker who already has operating system-level access to bypass Secure Boot protections. Secure Boot is a security standard designed to ensure that only trusted software is loaded during the boot process, protecting against bootkits and rootkits. The vulnerability allows an OS-resident attacker to leverage the enabled UEFI Shell to circumvent Secure Boot, potentially enabling the execution of unauthorized code during system startup. The CVSS v3.1 base score is 6.7, categorized as medium severity, reflecting the fact that exploitation requires local privileges (AV:L) and high privileges (PR:H), but no user interaction is needed (UI:N). The impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H), indicating that successful exploitation could lead to full system compromise. There are no known exploits in the wild at the time of publication, and no patches have been linked yet. The vulnerability is tracked under CWE-1188, which relates to insecure default configurations. This issue highlights the importance of secure default settings in firmware components, especially those involved in the boot process and security mechanisms like Secure Boot.

For European organizations, this vulnerability poses a significant risk primarily in environments where Ubuntu is deployed on systems relying on Secure Boot for firmware-level security. Organizations using Ubuntu EDK II on servers, workstations, or embedded devices could face potential local privilege escalation scenarios. An attacker with existing OS-level access could exploit this vulnerability to bypass Secure Boot, allowing them to load unauthorized or malicious firmware components or bootloaders. This could lead to persistent malware infections, rootkits, or firmware-level backdoors that are difficult to detect and remove. Critical infrastructure sectors such as finance, healthcare, government, and industrial control systems that rely on Ubuntu-based systems with Secure Boot enabled may be particularly at risk. The ability to bypass Secure Boot undermines the trustworthiness of the boot process, potentially leading to data breaches, system integrity violations, and prolonged unauthorized access. Although exploitation requires high privileges and local access, insider threats or attackers who have already compromised a system could leverage this vulnerability to deepen their control and evade detection. The lack of known exploits in the wild provides some immediate relief, but the medium severity score indicates that timely mitigation is necessary to prevent future attacks.

1. Disable the UEFI Shell in the EDK II firmware configuration if it is not explicitly required. This can be done by reviewing and modifying the firmware build settings or configuration files to ensure the shell is not enabled by default. 2. Apply any available firmware or Ubuntu EDK II updates from Canonical as soon as they are released to address this vulnerability. Monitor Canonical’s security advisories for patches or mitigations. 3. Restrict local administrative access to systems running Ubuntu with EDK II to trusted personnel only, minimizing the risk of an attacker gaining the required OS-level privileges. 4. Implement robust endpoint detection and response (EDR) solutions capable of detecting unusual firmware or bootloader modifications that could indicate exploitation attempts. 5. Enforce strict Secure Boot policies and verify Secure Boot status regularly to detect any unauthorized changes or bypass attempts. 6. Conduct regular security audits and penetration testing focusing on firmware and boot process security to identify potential weaknesses. 7. For environments where disabling the UEFI Shell is not feasible, consider additional hardening measures such as secure boot key management and hardware-based root of trust mechanisms to limit the impact of this vulnerability.