Critical Linux kernel flaw allows remote root attacks on MPTCP servers

Anthropic researchers built a working exploit for a severe Linux kernel bug, CVE-2026-98432, that lets an unauthenticated attacker gain remote root access on servers using Multipath TCP (MPTCP) listeners, and can also impact plain TCP connections. The use-after-free flaw sits in the IPv4 TCP stack's handling of connection requests, scored 9.8 by the Linux kernel CVE team, though Red Hat rates it lower (5.9) as a denial-of-service issue since triggering the race condition is non-trivial. An unreleased Claude AI model reportedly chained the bug with a KASLR bypass to achieve root code execution in about 53 minutes on an MPTCP-enabled host. The issue affects kernels from version 4.4 onward across Ubuntu, RHEL 8/9/10, Rocky Linux 8/9/10, and Debian, with some distros still awaiting full patches as of late October, while Debian 12 and 13 have already shipped fixed kernel packages; no in-the-wild exploitation has been confirmed yet.