CVE-2024-56690 is a vulnerability identified in the Linux kernel's cryptographic subsystem, specifically within the pcrypt module responsible for encryption and decryption operations. The issue arises from the handling of parallelized cryptographic operations when CPUs go online or offline. Since commit 8f4f68e7, the pcrypt operations return the error code -EAGAIN under these CPU state changes, signaling a temporary inability to process the request. However, in the alg_test() function, this error triggers a WARN log, which, if the kernel is configured with panic_on_warn=1, causes an unnecessary kernel panic. This panic is due to the system treating the warning as a critical failure, leading to a denial of service (DoS) condition. The root cause is the use of parallelized processing (padata_do_parallel()) which returns -EBUSY, and the fix involves bypassing the parallelization by calling the crypto layer directly in these cases to avoid the panic. This vulnerability affects multiple Linux kernel versions identified by their commit hashes, indicating it is present in recent kernel builds prior to the fix. The vulnerability does not require user interaction or authentication to trigger but depends on CPU hotplug events (CPU going online/offline), which can be common in virtualized or dynamically managed environments. No known exploits are reported in the wild as of the publication date, and no CVSS score has been assigned yet.

For European organizations, this vulnerability poses a risk primarily in environments where Linux kernels are deployed with panic_on_warn enabled, which is common in high-availability or security-sensitive systems that enforce strict kernel error handling policies. The vulnerability can lead to unexpected kernel panics and system crashes during CPU hotplug events, causing service interruptions and potential denial of service. This is particularly impactful for data centers, cloud providers, and enterprises relying on Linux-based infrastructure for critical services. The cryptographic operations affected are fundamental to secure communications and data protection, so instability in this subsystem could undermine trust in system reliability. Although no direct data breach or privilege escalation is indicated, the availability impact can disrupt business operations and lead to downtime, which may have regulatory and compliance implications under European data protection laws such as GDPR. Systems using dynamic CPU scaling or virtualization technologies (common in European cloud and telecom sectors) are more susceptible to triggering this vulnerability.

Organizations should promptly update their Linux kernels to versions that include the fix for CVE-2024-56690, which involves the patch that bypasses parallelized crypto calls when CPUs go online/offline. Specifically, kernel maintainers and system administrators should track and apply the commit 8f4f68e7 or later stable releases that address this issue. Additionally, review kernel configurations to assess the necessity of panic_on_warn=1; if feasible, temporarily disabling this setting can reduce the risk of kernel panics while patches are applied. Monitoring CPU hotplug events and minimizing unnecessary CPU online/offline cycles can also reduce exposure. For virtualized environments, ensure hypervisor and guest OS configurations do not frequently trigger CPU hotplug events unnecessarily. Implement robust system monitoring and alerting to detect kernel panics early and automate recovery procedures to minimize downtime. Finally, conduct thorough testing in staging environments before deploying patched kernels in production to avoid regressions.