Risky Bulletin: PwnEscape vulnerability lets you escape KVM

Linux kernel maintainers have fixed a serious flaw, dubbed PwnEscape and tracked as CVE-2026-99999, that allowed a virtual machine guest to break out of the KVM hypervisor module and execute code on the host system. The issue stems from the Linux networking stack letting a guest alter IP packets after the kernel had already marked them as validated, giving an attacker a path to read and potentially overwrite host memory. Because the flaw affects KVM on x86 hardware—the backbone of most cloud platforms, CI/CD systems, sandboxes, and AI infrastructure—its potential blast radius is considered larger than earlier KVM escape bugs like ITscape, Januscape, and Zapscape, since it abuses the networking layer rather than narrow configuration edge cases. Researcher Paulos Yibelo of Pwn.ai found PwnEscape using AI-assisted vulnerability research while competing in Vercel's $1 million sandbox-escape bug bounty, earning the contest's top $50,000 payout and its only Critical-rated submission.