CVE-2025-61661 is a vulnerability in the GNU GRUB2 bootloader stemming from an incorrect calculation of buffer size during string conversion when reading information from USB devices. Specifically, GRUB2 mishandles length values, leading to inconsistent buffer size allocation. This flaw can be exploited by a local attacker who has physical access to the machine and can connect a maliciously crafted USB device during the boot sequence. The attacker does not require privileges or user interaction, but the attack complexity is high due to the need to precisely craft the USB device and time the connection during boot. Successful exploitation causes GRUB2 to crash, resulting in a denial of service that prevents the system from booting properly. There is also a potential for data corruption, although this is less likely given the complexity of the exploit and the bootloader context. The vulnerability affects all versions of GRUB2 as no specific version range is provided, indicating a broad impact on Linux systems using this bootloader. No known exploits are currently in the wild, and no patches have been linked yet. The CVSS v3.1 score is 4.8 (medium), reflecting the limited attack vector (physical access) and high attack complexity but significant impact on availability. This vulnerability is particularly relevant for environments where physical security is less stringent or where USB boot devices are enabled by default.

For European organizations, the primary impact is operational disruption due to denial of service at boot time, potentially causing downtime for critical Linux-based servers or workstations. This can affect industries relying on Linux infrastructure such as finance, manufacturing, telecommunications, and government services. Data corruption risk, while low, could lead to integrity issues in boot configuration or system files, complicating recovery. Organizations with less controlled physical access environments, such as shared office spaces or data centers with multiple tenants, face higher risk. The inability to boot systems can delay incident response and recovery, impacting business continuity. Additionally, the need to physically access devices to exploit limits remote attack vectors but raises concerns for on-site security policies. The threat is less severe for cloud providers or environments where physical access is tightly controlled. However, embedded systems or IoT devices using GRUB2 and exposed to physical access could also be affected.

1. Restrict physical access to critical systems to prevent unauthorized USB device connections during boot. 2. Disable USB boot in BIOS/UEFI settings where not required to eliminate the attack vector. 3. Monitor and control boot device policies using secure boot mechanisms and firmware passwords. 4. Apply GRUB2 patches promptly once available from GNU or Linux distribution vendors. 5. Implement endpoint security controls that detect and block unauthorized USB devices. 6. Maintain regular backups and recovery plans to mitigate potential data corruption or system downtime. 7. Educate IT staff and users about the risks of connecting unknown USB devices, especially during system startup. 8. For high-security environments, consider hardware-based protections such as USB port locks or tamper-evident seals. 9. Audit and review bootloader configurations and logs to detect anomalies related to USB device interactions during boot.