CVE-2024-40956 is a vulnerability identified in the Linux kernel's dmaengine subsystem, specifically within the idxd driver component. The issue arises from improper handling of a linked list during interrupt processing in the irq_process_work_list function. The vulnerability is a Use-After-Free (UAF) condition caused by the reuse of a descriptor that has already been freed via the idxd_desc_complete() function. The root cause is that the list iterator does not safely handle deletion of entries during iteration, leading to a race condition where another thread may reuse the freed descriptor before it is removed from the list. This can result in memory corruption, potentially causing kernel crashes, data corruption, or privilege escalation if exploited. The fix involves using the list_for_each_entry_safe() macro to safely iterate and delete entries from the list during processing, preventing the UAF scenario. Although no known exploits are currently reported in the wild, the vulnerability affects Linux kernel versions identified by the commit hash 16e19e11228ba660d9e322035635e7dcf160d5c2 and similar. Given the kernel's critical role in system operation, this vulnerability poses a significant risk if exploited, especially in environments where the idxd driver is active and handling DMA operations.

For European organizations, the impact of CVE-2024-40956 could be substantial, particularly for enterprises and service providers relying on Linux-based infrastructure that utilizes the dmaengine idxd driver for high-performance data movement tasks. Successful exploitation could lead to kernel crashes, resulting in denial of service, or potentially allow attackers to execute arbitrary code with kernel privileges, compromising system confidentiality and integrity. This is especially critical for sectors such as finance, telecommunications, healthcare, and critical infrastructure, where Linux servers are prevalent. Additionally, data centers and cloud providers in Europe running Linux kernels with the vulnerable idxd driver may face operational disruptions and increased risk of targeted attacks. The absence of known exploits currently reduces immediate risk, but the vulnerability's nature means it could be weaponized in the future, necessitating proactive mitigation.

European organizations should prioritize updating their Linux kernels to versions that include the patch addressing CVE-2024-40956. Specifically, they should ensure that their kernel versions incorporate the fix that replaces unsafe list iteration with list_for_each_entry_safe() in the irq_process_work_list function. System administrators should audit their environments to identify systems running the affected kernel versions and the idxd driver. Where immediate patching is not feasible, organizations can consider temporarily disabling the idxd driver if it is not critical to operations, to reduce attack surface. Additionally, implementing kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR), Control Flow Integrity (CFI), and enabling kernel lockdown modes can help mitigate exploitation risks. Continuous monitoring for unusual kernel behavior or crashes related to dmaengine operations should be established. Finally, organizations should maintain up-to-date intrusion detection systems capable of identifying exploitation attempts targeting kernel vulnerabilities.