CVE-2021-47152 is a vulnerability identified in the Linux kernel's implementation of Multipath TCP (MPTCP), a protocol extension that allows multiple TCP paths to be used simultaneously for a single connection to improve redundancy and throughput. The vulnerability arises from a flaw in the function 'mptcp_frag_can_collapse_to()' which incorrectly assumes that only MPTCP uses a particular memory structure called 'page_frag'. In reality, other protocols such as plain TCP can also allocate page fragments. This incorrect assumption can lead to the reuse of already allocated memory for MPTCP data fragments, causing data stream corruption. Specifically, when forcing a TCP transparent proxy to use MPTCP for inbound connections, the memory management error can result in overlapping or corrupted data fragments. The fix ensures that the data fragment to be expanded is located at the current end of the page fragment, preventing memory reuse issues. This vulnerability was reported by a security researcher named Maxim, who also provided a clean reproducer to demonstrate the issue. The vulnerability affects certain Linux kernel versions identified by specific commit hashes and was publicly disclosed in March 2024. There are no known exploits in the wild at this time, and no CVSS score has been assigned yet.

For European organizations, this vulnerability could lead to data corruption in network communications that utilize MPTCP, particularly in environments where TCP transparent proxies are configured to use MPTCP for inbound connections. This could degrade the integrity and reliability of network data streams, potentially causing application errors, data loss, or unexpected behavior in critical services relying on Linux servers. While it does not directly enable remote code execution or privilege escalation, the corruption of data streams could disrupt business operations, especially in sectors relying heavily on high-availability and high-throughput network communications such as telecommunications, cloud service providers, and financial institutions. The lack of known exploits reduces immediate risk, but the vulnerability could be leveraged in targeted attacks or combined with other vulnerabilities to cause denial of service or data integrity issues. Given the widespread use of Linux in European data centers, cloud infrastructure, and embedded systems, the impact could be significant if unpatched systems are exposed to relevant network traffic patterns.

European organizations should prioritize updating their Linux kernel to versions that include the fix for CVE-2021-47152. Specifically, they should apply kernel patches that address the memory management in the MPTCP implementation, ensuring the corrected handling of page fragments. Network administrators should audit configurations involving TCP transparent proxies and MPTCP usage to identify potentially vulnerable setups. Where immediate patching is not feasible, organizations can consider disabling MPTCP or the use of TCP transparent proxies with MPTCP until patches are applied. Monitoring network traffic for anomalies that might indicate data corruption or unusual retransmissions can help detect exploitation attempts. Additionally, organizations should maintain robust backup and recovery procedures to mitigate the impact of any data integrity issues. Coordination with Linux distribution vendors for timely patch deployment and testing in staging environments is recommended to avoid service disruptions.