FreeBSD vulnerability has been fixed (CVE-2026-4747), which allows code execution at the kernel level to be achieved by sending network packets to an NFS server. The problem occurs when using the kgssapi.ko module, which implements the RPCSEC_GSS API on the kernel side. In addition to the kernel, the vulnerability affects user space applications that use the librpcgss_sec library and perform RPC server functions. Such applications, which are not part of the base FreeBSD system, can also be attacked by sending network packets.
The problem is present in the implementation of the GSS (Generic Security Services) API, which allows you to establish secure, authenticated communication channels with the server. RPCSEC_GSS is used in NFS servers to protect access to Sun RPC using Kerberos-based authentication and encryption of traffic between the server and client. The problem is caused by the fact that when verifying the signature, the data from the packet is copied to a fixed buffer without properly checking the size. The error occurs at the pre-authentication stage, but requires the ability to send network packets to the NFS server. An exploit is available that allows you to remotely run /bin/sh with root rights.
The vulnerability was identified by an Anthropic employee using the AI assistant Claude. It is noteworthy that third-party researchers from the Calif team used Claude to write a working exploit, passing only the general vulnerability report published by the FreeBSD project as information. In addition to directly exploiting the vulnerability, the AI model deployed a virtual machine with a vulnerable configuration, configured remote debugging and reading kernel crash dumps, and also organized the launch of /bin/sh in the exploit after achieving code execution at the kernel level. 4 hours of the Claude model’s time were spent on creating the exploit.
The researchers who created the exploit did not stop there and continued experiments, using Claude to identify vulnerabilities in Vim and Emacs, allowing their code to be executed when opened in specially designed editors files. It is