Fix and Troubleshooting for the Linux IPv4 TCP Handshake Use-After-Free Vulnerability CVE-2026-98432

The Linux stable kernel fixed a use-after-free vulnerability, CVE-2026-98432, in the IPv4 TCP handshake path on October 11 and 15. The kernel CNA rated it CVSS 3.1 9.8 Critical, affecting versions 4.4 and later. As of October 29, kernels for all Ubuntu versions are still marked as affected, and the default kernels of RHEL 8, 9, and 10 and Amazon Linux 2 have no fix yet. Anthropic said its Claude model wrote, in a lab setting, remote root exploit code targeting servers with a multipath TCP listener, but did not disclose it.