Linux servers running Multipath TCP (MPTCP) could be vulnerable to remote code execution through a flaw in the kernel’s networking stack.
Anthropic has disclosed a zero-click exploit developed with an unreleased Claude research model that allows an unauthenticated attacker to execute arbitrary commands as root, without requiring any user interaction.
Tracked as CVE-2026-98432, the vulnerability is a race-condition-induced use-after-free (UAF) bug in the Linux kernel. Anthropic demonstrated how an attacker could exploit the flaw remotely to leak kernel memory, defeat Kernel Address Space Layout Randomization (KASLR), hijack kernel control flow, and ultimately execute an attacker-controlled shell command.
The research is part of Anthropic’s broader effort to evaluate AI models’ ability to discover and exploit vulnerabilities in widely deployed software. The company disclosed five exploit chains involving Chrome, Safari, Android, Windows, and Linux to demonstrate how its internal model could combine multiple weaknesses into functional attacks.
Anthropic’s proof of concept for the Linux exploit took approximately 53 minutes to progress from the initial memory leak to successful root-level command execution, the company said in a blog post.
A TCP connection race leaves kernel memory exposed
According to a Linux kernel CVE advisory, the underlying flaw involves how Linux manages IP options during IPv4 TCP connection establishment. When a new connection is created, the kernel can transfer ownership of IP options from a pending connection request to the newly created socket without making a separate copy.
The problem arises when another CPU is simultaneously processing a retransmitted connection request and using those same options to construct a synchronize-acknowledge (SYNACK) response. If the child socket is freed before the second CPU finishes accessing the options, the kernel can end up reading memory that has already been released.
This creates a use-after-free condition. The upstream fix addresses the memory-management problem by deferring the release of the affected objects until after a read-copy-update (RCU) grace period, giving concurrent readers time to finish accessing them.
The flaw received a critical severity score of 9.8 and affects eight Linux kernel branches, dating back to version 4.4. Fixed releases include 5.10.272, 5.15.223, 6.6.159, 6.1.190, 6.12.113, 6.18.56, 7.2.10 and 7.3-rc7.
For users who obtain Linux through distributions such as Debian, Oracle Linux, SUSE, and Amazon Linux, fixed kernel packages are available for at least some releases. Ubuntu and Red Hat Enterprise Linux, however, had yet to release patched kernels as of October 30.
MCTCP listeners create the remote attack surface
Anthropic’s exploit specifically targets Linux servers running an MPTCP listener. MPTCP extends conventional TCP by allowing a device to use multiple network interfaces simultaneously within a single connection. This enables bandwidth aggregation, improved network selection, and failover when one network path becomes unavailable.
Linux implements MPTCP through its networking stack, but the protocol is opt-in: applications must explicitly request it when creating sockets, although mechanisms such as eBPF and other configuration techniques can also force applications to use it.
Administrators are advised to review their kernel versions, apply the relevant security updates, and assess whether their systems expose MPTCP listeners.
No Responses