Overview
CVE-2025-2486 is a security vulnerability affecting Ubuntu’s edk2 UEFI firmware packages. This flaw accidentally allowed the UEFI Shell to be accessed in Secure Boot environments, potentially leading to a bypass of Secure Boot constraints. While the severity isn’t officially rated, the implications of bypassing Secure Boot are significant.
This vulnerability is addressed in versions 2024.05-2ubuntu0.3 and 2024.02-2ubuntu0.3, which disable the UEFI Shell. Some previous versions attempted to mitigate the issue by implementing secure-boot-based decisions to continue running inside the Shell, aiming to enforce Secure Boot restrictions. This fix builds upon the incomplete solution for CVE-2023-48733, indicating a continued effort to harden the UEFI firmware.
Technical Details
The root cause of CVE-2025-2486 lies in the improper configuration of the edk2 UEFI firmware packages within Ubuntu. Specifically, the unintentional exposure of the UEFI Shell within a Secure Boot environment presented an attack vector. The UEFI Shell is a powerful pre-boot environment that, when unrestricted, can be leveraged to modify system boot parameters, load unsigned code, and ultimately bypass Secure Boot’s integrity checks.
The mitigation strategy involves disabling the UEFI Shell in the affected versions. Earlier attempts focused on controlling the shell’s actions based on Secure Boot status. While the details of this mechanism are not fully described, it can be assumed that secure variables or measurements were used to ensure only authorised code could be executed within the shell after Secure Boot was activated. The final solution however prefers disabling the shell entirely.
CVSS Analysis
Currently, CVE-2025-2486 has a CVSS score of N/A, indicating that a formal risk assessment has not yet been performed or published. However, based on the potential impact of a successful Secure Boot bypass, it is reasonable to assume a significant risk, especially in environments where Secure Boot is relied upon as a core security control. A realistic estimation, depending on exploitability, could put this in the medium to high severity range, were it to be scored.
Possible Impact
The exploitation of CVE-2025-2486 could have severe consequences:
- Secure Boot Bypass: Attackers could circumvent Secure Boot protections, allowing them to load and execute malicious code during the boot process.
- Malware Installation: Malicious actors could install persistent malware at the firmware level, making it difficult to detect and remove.
- Data Theft: By gaining control of the system before the operating system loads, attackers could potentially intercept sensitive data or modify system configurations for data exfiltration.
- System Compromise: A successful Secure Boot bypass could lead to complete system compromise, giving attackers full control over the affected device.
Mitigation or Patch Steps
The recommended mitigation for CVE-2025-2486 is to update your Ubuntu systems to the patched edk2 UEFI firmware packages. Specifically, ensure you are running version 2024.05-2ubuntu0.3 or 2024.02-2ubuntu0.3 or later.
- Update your system: Use the standard Ubuntu update mechanism (e.g., `sudo apt update && sudo apt upgrade`) to install the latest available updates.
- Verify the update: After updating, verify that the correct edk2 UEFI firmware package version is installed. Instructions will depend on the specifics of your server.
- Reboot the system: A reboot may be necessary for the updated firmware to take effect.
- Monitor for anomalies: After the update, carefully monitor your system for any unusual behavior.
