Anthropic reports Claude exploit for Linux kernel flaw

Anthropic says its report details five exploit chains that produced remote code execution or other critical impacts with little to no user interaction.[1] In one chain, Claude produced an exploit that allowed a remote attacker to run arbitrary commands as root on a Linux server with an MPTCP listener, without credentials or user interaction.[1] Anthropic says the attack remotely defeats kernel address space layout randomization (KASLR) in its first stage.[1] Its proof of concept took 48 minutes to leak a kernel pointer, then five more minutes to execute a shell command.[1]

CVE-2026-98432 is a use-after-free flaw in the Linux kernel’s IPv4 TCP networking code.[3] The race can occur when one thread handles a retransmitted SYN as another establishes the connection, leading to access to freed connection-option memory.[4] The issue was introduced in Linux 4.4 and fixed in Linux 6.12.113.[5] Although Anthropic’s demonstrated root-level exploit used an MPTCP listener, the flaw also affects ordinary TCP connections; remote code execution has not been publicly demonstrated on systems without an MPTCP listener.[1][3]

Multipath TCP (MPTCP) allows one connection to use multiple network paths to improve performance and reliability.[3] Go 1.24 enables MPTCP by default for TCP listeners on Linux when the kernel supports the feature.[3] That makes it important to assess MPTCP use, but disabling it alone does not fix the underlying vulnerability, which can still be triggered through ordinary TCP traffic.[3] AlmaLinux says dropping incoming IPv4 TCP packets carrying IPv4 options blocks the trigger without affecting regular connections.[6] BleepingComputer reports no confirmed exploitation of CVE-2026-98432 in the wild.[3]

Anthropic says the vulnerability was patched upstream and backported to all maintained stable kernel branches, and the kernel CVE team recommends updating to the latest stable version.[1][5] Distribution fixes are not uniform: as of October 30, Ubuntu 22.04 LTS, 24.04 LTS, 26.04 LTS and 26.10 remained vulnerable, with fixes in progress, while RHEL 8, 9 and 10 had fixes planned for future updates.[3] Debian listed fixed packages for Debian 12 and 13.[3] AlmaLinux said patched kernels were available in its testing repository and requested community verification before production release.[6]