CVE-2025-1125 is a vulnerability in the GRUB bootloader's HFS filesystem module that arises from improper handling of integer overflows during buffer size calculations. Specifically, when reading data from an HFS filesystem, GRUB uses user-controlled metadata parameters to calculate the size of internal buffers. However, it fails to properly check for integer overflows, which can cause the buffer size calculation to wrap around and result in a smaller-than-expected allocation via grub_malloc(). Subsequently, the hfsplus_open_compressed_real() function writes data beyond the allocated buffer boundary, causing an out-of-bounds write. This memory corruption can overwrite critical internal GRUB data structures, potentially allowing an attacker to execute arbitrary code within the bootloader context. Such code execution can bypass secure boot protections, undermining system integrity from the earliest stage of the boot process. The vulnerability requires local access to a maliciously crafted HFS filesystem image and some user interaction to trigger the vulnerable code path. The CVSS v3.1 base score is 7.8, reflecting high impact on confidentiality, integrity, and availability, with low attack complexity and no privileges required but user interaction needed. No public exploits have been reported yet. The flaw affects GRUB versions that include the vulnerable HFS module, commonly found in systems that support booting from or mounting HFS filesystems, such as dual-boot macOS/Linux setups or recovery environments.

For European organizations, this vulnerability poses a significant risk to systems that utilize GRUB bootloader with HFS filesystem support, particularly in environments where macOS or HFS-formatted drives are accessed or dual-boot configurations exist. Successful exploitation could allow attackers to bypass secure boot protections, leading to persistent, low-level compromise that is difficult to detect and remediate. This could result in unauthorized access to sensitive data, system integrity breaches, and potential disruption of critical services. Sectors such as finance, government, and critical infrastructure that rely on secure boot mechanisms and may use mixed OS environments are particularly at risk. Although exploitation requires local access and user interaction, the ability to execute arbitrary code at bootloader level elevates the threat to a high severity. The lack of known exploits in the wild currently reduces immediate risk but does not diminish the urgency for mitigation given the potential impact.

European organizations should implement the following specific mitigations: 1) Monitor for and apply GRUB updates and patches addressing CVE-2025-1125 as soon as they become available from trusted vendors or distributions. 2) Restrict and monitor access to removable media and external drives formatted with HFS filesystems to prevent introduction of malicious filesystems. 3) Employ strict validation and scanning of filesystems before mounting or booting, including using filesystem integrity tools that can detect anomalies in HFS metadata. 4) Harden boot configurations by disabling unnecessary filesystem modules in GRUB if HFS support is not required. 5) Enforce strong physical and logical access controls to prevent unauthorized local access to systems. 6) Use secure boot configurations that include measured boot and runtime attestation to detect unauthorized bootloader modifications. 7) Educate users about the risks of mounting untrusted filesystems and require administrative approval for such actions. 8) Implement endpoint detection and response (EDR) solutions capable of monitoring bootloader integrity and unusual filesystem activity. These targeted actions go beyond generic advice by focusing on controlling exposure to malicious HFS filesystems and strengthening bootloader security.