Linux kernel TCP flaw affects Ubuntu, Red Hat and other distributions

From the article:

A flaw in the Linux kernel's TCP code, tracked as CVE-2026-98432, affects Ubuntu, Red Hat Enterprise Linux (RHEL), and other Linux distributions. The kernel's own CVE team rates it 9.8 out of 10 on the CVSS scale.

Anthropic said on October 27 that its AI model wrote an exploit that uses the flaw to let a remote attacker with no credentials run commands as root on Linux servers with a multipath TCP listener.

[...]

The flaw is a race condition in the code that sets up new IPv4 TCP connections. It can make the kernel read memory it has already freed, a bug type known as a use-after-free.

The kernel fix credits Anthropic researcher Xinyang Ge with reporting the bug. Neither the CVE record nor the fix mentions multipath TCP (MPTCP). The link between that feature and this bug comes from Anthropic's post.

[...]

Anthropic's post says the flaw "was patched upstream and backported to all maintained stable kernel branches." For distribution users, that fix arrives only in the vendor's kernel package. Debian, Oracle Linux, SUSE, and Amazon Linux have shipped fixed packages, at least for some of their kernels, but Ubuntu and RHEL have not.

[...]

The kernel's CVE team added the 9.8 score to the CVE record on October 24, nine days after publishing the CVE.

Its score assumes an attacker who sends a TCP connection request carrying IPv4 Record Route or Timestamp options, then resends the request to try to win the race. The team rated attack complexity low, saying both sides of the race are "attacker-induced."

[...]

Red Hat's CVE page rates the flaw Moderate, scoring it 5.9 because the race is hard to win. It says the most likely result is a kernel crash, with memory corruption possible in theory, and that "no confidentiality or integrity impact has been demonstrated."

Red Hat's machine-readable advisory file, updated on October 29, lists the impact as Important and scores the flaw 8.1, with high confidentiality and integrity impact. Red Hat's bug tracker changed the issue's severity from medium to high the same day. On that day, the CVE page showed Moderate and 5.9.

From a Hacker News comment:

Exploitability over the internet is unlikely, most ISP routers drop packets with IP options fields.

Successful exploit requires multiple CPU cores to process packets, so systems with just a single core or packet processing pinned to a single core are not affected.