Linux kernel flaw allows KVM virtual machine guest host escape

Security researchers have discovered a critical vulnerability in the Linux kernel networking stack that allows attackers to escape Kernel-based Virtual Machine systems. CSO Online, The Register, and Mezha.net all report that the flaw allows a guest virtual machine to escape to the host system. CSO Online reported that the flaw can allow attackers to execute code on the host. [1][2][3]

The vulnerability is tracked as CVE-2026-99999 and named PwnEscape, according to CSO Online. The weakness originates in the IPv4 networking subsystem of the Linux host and involves checksum offloading. CSO Online reported that the bug could also allow attackers to compromise systems running other Linux-based virtualization and sandbox platforms. [1]

Linux is an open-source, Unix-like operating system kernel first released by Linus Torvalds on September 17, 1991. The monolithic kernel handles low-level hardware interactions and is licensed under the GNU General Public License version 2. Systems running Linux may also use systemd, a software suite designed to manage user space processes and services across distributions. [4][5]

CSO Online reported that researchers warned that similar bugs could exist elsewhere in the Linux networking stack. The security researchers have not yet detailed official patches or remediation steps for the flaw. [1]