Mitigations for CVE-2026-98432 [IPv4 TCP handshake use-after-free] (blog.rodmena.com)

On October 15, the Linux kernel CVE team disclosed CVE-2026-98432, a critical use-after-free vulnerability in the IPv4 TCP handshake process that poses a significant risk to Linux servers due to its potential for remote exploitation. This bug, which has existed since Linux version 4.4, can be triggered without user authentication, allowing attackers to execute remote root exploits on systems with open IPv4 TCP ports. Red Hat has rated the vulnerability with a critical score of 9.8, highlighting the urgency for mitigation. The technical details reveal that the flaw arises when a TCP SYN with options is processed; the kernel mistakenly frees memory while it is still in use, leading to a race condition. To address this, an upstream fix has been released that employs a grace period for memory freeing, alongside additional mitigation measures like blocking TCP packets with IP options using nftables. Anthropic's internal model identified the bug and developed an exploit, underscoring the necessity for immediate action. As organizations await stable kernel updates, the recommended mitigation steps, including disabling Multipath TCP and controlling memory access via network namespaces, are essential to minimizing the risk of exploitation.