CVE-2025-1125 is a vulnerability in the GRUB bootloader's HFS filesystem module that arises due to improper handling of integer overflows during buffer size calculations. Specifically, when GRUB reads data from an HFS filesystem, it uses parameters derived from filesystem metadata to determine the size of internal buffers. However, these parameters are not properly validated for integer overflow conditions. An attacker can craft a malicious HFS filesystem with manipulated metadata that causes the buffer size calculation to overflow, resulting in grub_malloc() allocating a smaller buffer than intended. Subsequently, the hfsplus_open_compressed_real() function writes beyond the allocated buffer boundary, causing an out-of-bounds write. This memory corruption can overwrite critical GRUB internal data structures, potentially leading to arbitrary code execution within the bootloader context. Notably, this exploit can bypass secure boot protections, which normally prevent unauthorized code execution during system startup. The attack requires local access with low privileges and user interaction, as the attacker must provide or mount the malicious HFS filesystem. The CVSS v3.1 base score is 6.7 (medium severity), reflecting the complexity of exploitation and the significant impact on confidentiality, integrity, and availability. No patches or known exploits are currently publicly available, but the vulnerability is published and should be addressed promptly. This flaw is particularly relevant for systems that use GRUB as their bootloader and support HFS filesystems, such as dual-boot or macOS interoperability environments.

For European organizations, this vulnerability poses a risk primarily to systems that utilize the GRUB bootloader with HFS filesystem support enabled. Organizations that manage heterogeneous environments involving macOS or legacy HFS volumes, such as software development firms, media companies, or enterprises with mixed OS deployments, are more exposed. Successful exploitation can lead to arbitrary code execution at boot time, allowing attackers to bypass secure boot protections and potentially implant persistent bootkits or rootkits. This compromises system integrity and confidentiality, and can disrupt availability by corrupting bootloader data. Critical infrastructure sectors relying on secure boot processes, such as finance, healthcare, and government agencies, may face heightened risks. Although exploitation requires local access and user interaction, insider threats or social engineering attacks could leverage this vulnerability. The lack of known exploits in the wild currently reduces immediate risk, but the potential for future weaponization necessitates proactive mitigation.

1. Monitor official GRUB and Linux distribution security advisories for patches addressing CVE-2025-1125 and apply them promptly once available. 2. Audit systems to identify those using GRUB with HFS filesystem support and assess the necessity of mounting or accessing HFS volumes; disable HFS support if not required. 3. Restrict physical and logical access to systems to prevent untrusted users from introducing malicious HFS filesystems, including controlling USB and external media usage. 4. Implement strict user privilege management to limit low-privilege users' ability to mount or interact with filesystems that could trigger this vulnerability. 5. Employ endpoint detection and response (EDR) tools to monitor for anomalous bootloader behavior or unauthorized modifications to boot components. 6. Educate users and administrators about the risks of mounting untrusted filesystems and the importance of secure boot integrity. 7. Consider deploying secure boot policies that include firmware-level protections and validation of bootloader integrity beyond GRUB's internal checks.