CVE-2025-0678 is a vulnerability identified in the GRUB2 bootloader, specifically within its squash4 filesystem module. The flaw stems from improper handling of integer overflows during buffer size calculations when reading data from a squash4 filesystem. The module uses parameters derived from the filesystem geometry, which can be controlled by an attacker, to determine buffer sizes. Due to inadequate overflow checks, these calculations can wrap around, causing grub_malloc() to allocate a smaller buffer than intended. Consequently, the direct_read() function may perform a heap-based out-of-bounds write when reading data, leading to corruption of GRUB's internal critical data structures. This memory corruption can be exploited to achieve arbitrary code execution within the bootloader context, effectively bypassing secure boot protections. The vulnerability requires local access with low privileges (PR:L), no user interaction (UI:N), and has low attack complexity (AC:L). The scope is unchanged (S:U), but the impact on confidentiality, integrity, and availability is high (C:H/I:H/A:H). Although no known exploits are currently in the wild, the potential for severe impact on system boot integrity and security is significant. The vulnerability affects GRUB2 versions using the squash4 filesystem module, which is commonly found in Linux distributions that support squashfs compressed filesystems.

For European organizations, this vulnerability poses a critical risk to systems that use GRUB2 as their bootloader, particularly those employing squash4 filesystems. Successful exploitation can lead to arbitrary code execution at the bootloader level, allowing attackers to bypass secure boot mechanisms and gain persistent, stealthy control over affected systems. This undermines the integrity and trustworthiness of the boot process, potentially enabling further compromise of sensitive data and critical infrastructure. Organizations in sectors such as finance, healthcare, government, and critical infrastructure, which rely heavily on secure boot and Linux-based systems, could face significant operational disruptions and data breaches. The requirement for local access reduces the risk of remote exploitation but elevates the threat from insider attacks or attackers who have already gained limited access. The high confidentiality, integrity, and availability impacts mean that exploitation could lead to data theft, system downtime, and loss of trust in security controls.

1. Apply official patches and updates for GRUB2 as soon as they become available from Linux distribution vendors or GRUB maintainers. 2. Until patches are deployed, restrict local access to systems, especially limiting untrusted users from interacting with the bootloader or filesystem images. 3. Implement strict access controls and monitoring on systems that use squash4 filesystems to detect suspicious activities indicative of exploitation attempts. 4. Validate and sanitize all filesystem images before deployment, particularly those sourced from untrusted or external origins, to prevent maliciously crafted squash4 filesystems from being loaded. 5. Employ hardware-based secure boot mechanisms and ensure their configurations are hardened to detect unauthorized bootloader modifications. 6. Conduct regular security audits and penetration testing focused on bootloader and filesystem security to identify potential exploitation paths. 7. Educate system administrators about the risks of local privilege escalation and enforce the principle of least privilege to minimize attack surfaces.