CVE-2024-56740 is a vulnerability identified in the Linux kernel's implementation of NFSv3 (Network File System version 3), specifically related to the LOCALIO read path. The flaw arises because the kernel fails to clear the res.replen field in the nfs_local_read_done function. This omission leads to memory corruption due to stale or garbage data persisting in res.replen. The vulnerability chain begins when nfs3_read_done() copies this corrupted replen value into server->read_hdrsize. Subsequently, nfs3_proc_read_setup() transfers this corrupted value into args.replen for new NFSv3 read requests. The corrupted replen value is then passed through nfs3_xdr_enc_read3args() to rpc_prepare_reply_pages(), which uses it as hdrsize in xdr_init_pages. This causes the receive buffer length (rq_rcv_buf) to be set to an incorrect, excessively large value. The corrupted length is copied to rq_private_buf, and eventually xs_read_stream_request() passes a kvec structure to sock_recvmsg(), which then receives incoming data into an incorrect memory location. This sequence can lead to memory corruption, potentially causing data integrity issues or kernel crashes. The vulnerability is reproducible when NFSv3 LOCALIO reads are active and the server pivots back to normal RPC-based NFSv3 operations, such as during a server stop and restart under heavy read IO. This indicates a race or state management issue between LOCALIO and RPC modes in the NFSv3 client implementation in the Linux kernel. No known exploits are reported in the wild yet, and no CVSS score has been assigned. However, the technical details suggest a serious flaw in kernel memory handling related to NFSv3 reads, which could be exploited to cause denial of service or potentially escalate privileges if combined with other vulnerabilities.

For European organizations, this vulnerability poses a significant risk especially for enterprises relying heavily on Linux servers using NFSv3 for networked file storage and sharing. NFS is widely used in data centers, cloud environments, and enterprise storage solutions across Europe. Memory corruption in the kernel can lead to system instability, crashes, or denial of service, impacting availability of critical services. Furthermore, corrupted memory handling in kernel space can be leveraged by skilled attackers to execute arbitrary code or escalate privileges, threatening confidentiality and integrity of sensitive data. Organizations in sectors such as finance, telecommunications, government, and critical infrastructure that depend on Linux-based NFS storage are particularly vulnerable. The vulnerability could disrupt business continuity, cause data loss, or enable lateral movement within networks if exploited. Given the complexity of the issue, detection and remediation may require kernel updates and careful testing to avoid operational disruptions.

To mitigate this vulnerability, European organizations should prioritize applying the official Linux kernel patches that address the clearing of res.replen in nfs_local_read_done as soon as they become available. Until patches are deployed, organizations should consider the following specific measures: 1) Limit or disable the use of NFSv3 LOCALIO mode if possible, especially on critical servers, to reduce exposure to the vulnerable code path. 2) Implement strict controls on NFS server restarts or reconfigurations during heavy read IO to avoid triggering the vulnerable state transition. 3) Monitor kernel logs and system behavior for anomalies related to NFS reads or unexpected crashes that could indicate exploitation attempts. 4) Employ kernel hardening techniques such as Kernel Address Space Layout Randomization (KASLR) and Kernel Page Table Isolation (KPTI) to reduce exploitation risk. 5) Conduct thorough testing of kernel updates in staging environments to ensure stability before production deployment. 6) Use network segmentation and access controls to restrict NFS traffic to trusted hosts only, minimizing attack surface. 7) Maintain up-to-date backups of critical data to enable recovery in case of service disruption.