CVE-2021-47538 is a vulnerability identified in the Linux kernel's rxrpc (Remote Execution RPC) subsystem. The issue involves a resource leak caused by improper handling of references to the rxrpc_local structure during peer lookup operations. Specifically, the function rxrpc_lookup_peer() fails to call rxrpc_put_local() for a peer candidate before freeing the associated memory with kfree(). This omission results in a reference count leak, which can lead to resource exhaustion or memory corruption over time. The vulnerability was addressed by refactoring the code to properly abstract and manage the peer freeing process, ensuring that reference counts are decremented appropriately before memory is released. While the vulnerability does not have an assigned CVSS score and there are no known exploits in the wild, the flaw represents a subtle but important memory management error in a core Linux kernel networking component. The rxrpc protocol is used primarily for remote procedure calls in certain distributed systems and applications, so the impact depends on the deployment of this protocol in affected environments. The affected versions correspond to specific Linux kernel commits prior to the patch date of May 24, 2024.

For European organizations, the impact of CVE-2021-47538 depends largely on the extent to which they utilize Linux systems running the vulnerable kernel versions and specifically employ the rxrpc protocol. If exploited, the resource leak could degrade system stability, potentially leading to denial of service conditions due to memory exhaustion or kernel crashes. This could affect critical infrastructure, servers, or network devices relying on Linux, especially in sectors such as telecommunications, finance, and government services where Linux is prevalent. Although no active exploits are known, the vulnerability could be leveraged in targeted attacks aiming to disrupt services or cause system instability. The indirect impact includes increased operational costs due to system downtime and the need for emergency patching. Given the kernel-level nature of the flaw, successful exploitation could also undermine system integrity and availability, which are critical for compliance with European data protection and operational resilience regulations.

European organizations should prioritize applying the official Linux kernel patches that address CVE-2021-47538 as soon as they become available. Since the vulnerability involves kernel-level code, updating to the latest stable kernel version that includes the fix is the most effective mitigation. Organizations should audit their systems to identify Linux hosts running vulnerable kernel versions and assess whether the rxrpc protocol is in use. If rxrpc is not required, disabling or removing the related kernel modules can reduce the attack surface. Additionally, monitoring system logs for unusual kernel errors or memory leaks related to rxrpc can help detect potential exploitation attempts. Implementing strict access controls and network segmentation to limit exposure of vulnerable systems can further mitigate risk. Finally, maintaining robust backup and recovery procedures will help minimize operational impact in case of exploitation.