CVE-2024-35875 addresses a vulnerability in the Linux kernel specifically related to the x86 architecture on Confidential Computing (CoCo) systems. CoCo systems operate under a threat model where the virtual machine (VM) host is considered untrusted and may actively attempt to extract secrets or manipulate computations within guest VMs. In such environments, cryptographic operations and secure random number generation (RNG) are critical for maintaining confidentiality and integrity. The vulnerability arises because CoCo guests rely almost exclusively on the CPU's RDRAND instruction as the sole entropy source for seeding their RNG at boot time. If RDRAND is faulty or compromised due to hardware defects or malicious interference, the RNG cannot be properly seeded, leading to catastrophic failures in cryptographic operations. The Linux kernel patch enforces a strict requirement that at boot time, the RNG must be seeded with 256 bits of entropy from RDRAND. If this seeding fails, the system triggers a kernel panic, effectively halting the boot process to prevent insecure operation. This approach isolates the fix to the CoCo x86 driver rather than the core RNG subsystem, acknowledging that other platforms may have different entropy sources. The patch also leverages the add_device_randomness() interface to contribute entropy safely without degrading RNG quality. This vulnerability primarily impacts the initial boot phase, as subsequent entropy gathering is less dependent on RDRAND alone. No known exploits are reported in the wild, and the vulnerability was published on May 19, 2024.

For European organizations utilizing Linux-based CoCo systems, this vulnerability poses a significant risk to the confidentiality and integrity of sensitive computations and cryptographic keys. If RDRAND fails or is compromised, the RNG seeding process will fail, causing the system to panic and halt booting. While this prevents insecure operation, it also results in availability issues, potentially causing downtime for critical services relying on CoCo VMs. Organizations in sectors such as finance, healthcare, and government that deploy confidential computing for data protection and regulatory compliance may experience operational disruptions. Moreover, the reliance on hardware RNG means that hardware faults or supply chain attacks targeting CPU microcode or firmware could exacerbate the risk. The inability to boot securely could delay incident response or system recovery. However, since the vulnerability is contained to CoCo x86 platforms and triggers a fail-safe panic, it reduces the risk of silent compromise but increases the risk of availability impact during boot failures.

European organizations should ensure that their Linux kernel versions are updated to include the patch that enforces RDRAND seeding on CoCo systems. Specifically, they should: 1) Verify that all CoCo x86 systems run kernel versions incorporating the fix for CVE-2024-35875. 2) Conduct hardware validation to confirm that CPU RDRAND instructions operate correctly and are not affected by firmware or microcode issues. 3) Implement monitoring to detect kernel panics related to RNG seeding failures during boot, enabling rapid incident response. 4) Engage with hardware vendors to ensure supply chain integrity and timely microcode updates that maintain RDRAND reliability. 5) For critical environments, consider fallback entropy sources or architectural changes to reduce sole reliance on RDRAND, if feasible, while maintaining the CoCo threat model. 6) Document and test recovery procedures for systems that fail to boot due to this panic condition to minimize downtime. These steps go beyond generic patching by emphasizing hardware validation, monitoring, and operational preparedness specific to the CoCo threat model.