CVE-2024-40992 is a vulnerability identified in the Linux kernel's RDMA (Remote Direct Memory Access) subsystem, specifically affecting the rxe (RDMA over Ethernet) driver. The issue arises from improper handling of Unreliable Datagram (UD) request packets' length checking. According to the InfiniBand Architecture (IBA) specification, if a UD request packet has an invalid length, the responder should silently drop the packet and wait for a new request. However, a recent patch (commit 689c5421bfe0) intended to fix responder length checking introduced a regression. The function copy_data defers length checks for UD Queue Pairs (QPs), but when a packet size exceeds the receive buffer capacity, copy_data returns an error (-EINVAL). This causes send_data_in to return RESPST_ERR_MALFORMED_WQE, which transitions the UD QP into an ERROR state, effectively disrupting communication. This vulnerability does not appear to allow direct code execution or privilege escalation but can cause denial of service (DoS) by rendering RDMA UD QPs unusable. The vulnerability affects Linux kernel versions containing the specified commit and has been publicly disclosed without known exploits in the wild. No CVSS score has been assigned yet.

For European organizations, especially those relying on high-performance computing, data centers, or storage solutions utilizing RDMA over Ethernet, this vulnerability can lead to service disruptions. RDMA is commonly used in environments requiring low-latency, high-throughput networking such as financial institutions, research centers, and cloud service providers. The denial of service caused by UD QP error states could interrupt critical data transfers, degrade application performance, or cause cascading failures in clustered systems. While the vulnerability does not appear to compromise confidentiality or integrity directly, availability impacts could be significant in sectors where uptime and real-time data processing are critical. Organizations using Linux kernels with the affected commit in production environments should be aware of potential operational disruptions.

To mitigate this vulnerability, European organizations should: 1) Identify Linux systems running affected kernel versions containing commit 689c5421bfe0 and related patches. 2) Apply the latest kernel updates or patches from trusted Linux distributions that address this regression and restore proper length checking behavior. 3) Monitor RDMA subsystem logs for errors related to UD QP states transitioning to ERROR, which may indicate exploitation or triggering of the issue. 4) Implement network segmentation to isolate RDMA traffic where feasible, reducing exposure to malformed packets. 5) Engage with hardware and software vendors for firmware or driver updates that may complement kernel fixes. 6) Test patches in staging environments to ensure stability and avoid regressions before production deployment. 7) Consider fallback or alternative communication protocols temporarily if RDMA reliability is critical and patches are delayed.