In the Linux kernel, an uninitialized field in the mptcp_write_data_fin function occurs when a DATA_FIN packet is sent without payload. Because the checksum calculation relies on this field, an attacker could influence the checksum value or cause the kernel to transmit stale data, potentially leading to data integrity violations or memory disclosure. The bug is a classic case of improper use of an uninitialized variable and could affect any Linux kernel that processes MPTCP packets.

All Linux kernel releases that include the MPTCP subsystem are potentially affected. The issue is resolved only after the patch that restores zero‑initialization of the checksum field (commit cfcceb7a39fc). No specific version range is listed, so any kernel prior to the inclusion of that commit is at risk.

The CVSS score of 3.7 indicates low to moderate severity. Because the flaw involves an uninitialized variable in kernel packet handling, the impact could be limited to checksum corruption or memory disclosure during DATA_FIN transmission. The EPSS score is <1% (approximately 0.15%), indicating a very low probability of exploitation. The vulnerability is not listed in CISA's KEV catalog. The likely attack vector is via network traffic; an attacker crafting malicious MPTCP DATA_FIN packets could influence the checksum behavior or expose stale memory contents. No publicly known exploits exist, but the kernel‑level nature of the defect warrants vigilance.