CVE-2025-0677 is a medium-severity vulnerability affecting the GRUB2 bootloader's UFS (Unix File System) module. The flaw arises during the handling of symbolic link (symlink) lookups. Specifically, when GRUB2 attempts to read the symlink data, it checks the inode's data size to allocate a buffer for reading the file content. However, it fails to verify whether the symlink data size has overflowed, leading to an incorrect, smaller buffer allocation via grub_malloc(). Subsequently, when the grub_ufs_lookup_symlink() function reads the symlink data from disk, it writes beyond the allocated buffer boundary, causing an out-of-bounds write in the heap memory. This heap corruption can be exploited by an attacker who crafts a malicious filesystem image containing a specially designed symlink. Successful exploitation could enable arbitrary code execution within the bootloader context, potentially allowing attackers to bypass secure boot mechanisms and compromise the system's boot integrity. The vulnerability requires local access with high privileges (as indicated by CVSS vector AV:L/PR:H) and does not require user interaction. The attack complexity is high, reflecting the difficulty in crafting the malicious filesystem and triggering the flaw. No known exploits are currently reported in the wild, and no patches or vendor advisories are linked yet. The vulnerability impacts confidentiality, integrity, and availability due to the possibility of arbitrary code execution during system boot, which could lead to persistent system compromise.

For European organizations, this vulnerability poses a significant risk to systems relying on GRUB2 with UFS support, particularly in environments where secure boot is critical, such as government, financial institutions, and critical infrastructure sectors. Exploitation could allow attackers to bypass secure boot protections, leading to persistent malware infections or rootkits that are difficult to detect and remove. This undermines system integrity and trustworthiness from the earliest stage of system startup. Although exploitation requires local high-privilege access, the ability to craft malicious filesystems could be leveraged in multi-tenant environments, virtualized infrastructures, or scenarios involving removable media. The impact extends to data confidentiality and availability, as attackers could manipulate boot processes to exfiltrate data or cause denial of service. Given the medium CVSS score and the complexity of exploitation, the threat is moderate but should not be underestimated, especially in high-security environments.

Organizations should proactively monitor for updates and patches from GRUB2 maintainers and Linux distribution vendors, applying them promptly once available. In the interim, restrict high-privilege local access to trusted personnel only, and enforce strict controls on the use and mounting of external or untrusted filesystems, especially those using UFS. Employ integrity verification mechanisms for bootloader components and filesystem images, such as cryptographic signatures and secure boot policies, to detect unauthorized modifications. Consider disabling UFS support in GRUB2 if not required, reducing the attack surface. Regularly audit and monitor boot processes and logs for anomalies indicative of tampering. In virtualized or containerized environments, isolate bootloader components and limit filesystem exposure to untrusted sources. Finally, incorporate this vulnerability into incident response plans to ensure rapid containment and remediation if exploitation is suspected.