Critical PwnEscape Linux Kernel Vulnerability Lets Guest VMs Read Host Memory

Researchers at pwn.ai uncovered a critical Linux kernel bug, dubbed PwnEscape and tracked as CVE-2026-99999, that lets code running inside a guest virtual machine siphon memory from its host—and in lab conditions crash the host or even execute code on it. The flaw sits in the kernel's shared networking stack rather than in any single cloud vendor's configuration, meaning it could affect virtually any provider isolating tenants via the Linux kernel. The bug was first demonstrated against Vercel's production Vercel Sandbox environments, which rely on Firecracker microVMs on Amazon EC2 hardware, during a bug-bounty challenge, and Vercel has confirmed the finding while stating no customer data was actually exposed. A patch authored by Red Hat's Michael S. Tsirkin has been merged upstream and backported across stable branches (e.g., 5.10.272, 6.1.190, 6.6.159, 6.12.113, 6.18.57, 7.2.11); administrators should update host kernels promptly, as there is currently no known workaround and exploitation requires local code execution inside a guest. No active exploitation has been observed, but a public proof-of-concept exists.