Claude Wrote a Root-Level Linux Exploit. Ubuntu Is Still Exposed

Anthropic says Claude wrote a working exploit that lets an attacker seize total control of a Linux server over the internet — no password required. The flaw under it, CVE-2026-98432, has lurked in the Linux kernel since version 4.4 and rates 9.8 out of 10 on the severity scale. Anthropic detailed the attack on Oct. 27 in a research post spanning five targets: Chrome, Safari, Android, Windows and Linux. The Linux piece came from an unreleased internal Claude model after some initial prompting.

It doesn't take long. According to Anthropic, the exploit needs under an hour to locate a hidden spot in memory, then about five minutes more to fire off a command with root-level access. The mechanism is a race condition that plays out like reading a sticky note somebody already put through the shredder — one part of the system discards a piece of information while another part is still relying on it, per AlmaLinux. A crafted message that opens an internet connection is enough to set it loose.

Misses cost the attacker next to nothing, which makes persistence cheap. Anthropic noted that a lost race only fails the handshake rather than crashing the system, so an attacker can just keep retrying until it lands. The demonstrated version hinges on a target running multipath TCP, a feature that splits one connection across multiple routes. Go programs have had it switched on by default since Go 1.24, per the Go Security Team — though the team stressed the bug itself isn't MPTCP-specific.

Red Hat shipped fixes for RHEL 8, 9 and 10 on Sunday, including advisory RHSA-2026:93412. Debian, SUSE, Oracle Linux and Amazon Linux have also rolled out patches, at least for some versions. For anyone stuck on an unpatched box, Red Hat published a temporary firewall rule — with a caveat. It trims exposure but can't fully block the vulnerability, the company said in its security bulletin, and a complete fix is still in the works.

Ubuntu, one of Linux's most widely used flavors, is the glaring holdout. Its tracker still flags every release from 16.04 through 26.10 as vulnerable. Fixes for 22.04, 24.04, 26.04 and 26.10 show as in progress, while 20.04, 18.04 and 16.04 carry only a bare 'Vulnerable' label — and no release date is listed for any of them.

It's not Anthropic's first run at this. Decrypt reported in April that the company's earlier Claude Mythos model helped Mozilla surface 271 bugs in Firefox. Now the question is whether Ubuntu can close the gap before someone with worse intentions than a research post gets there first.