PwnEscape: Linux networking guest-to-host escape (CVE-2026-99999)
› Linux kernel networking (host side of KVM/Firecracker and similar)
- started
- Oct 8, 2026
- closed
- ongoing
- CVEs
- 1
- sources
- 5
## summary
Paulos Yibelo / pwn.ai found a Critical Linux networking flaw (CVE-2026-99999, CVSS 9.3) during Vercel’s $1M Sandbox challenge. Guest-controlled checksum metadata can rewrite an IPv4 header after validation, enabling host-memory disclosure and, in lab conditions, guest-to-host code execution on KVM/Firecracker. Upstream fix merged Oct 2026; host kernels need patch + reboot. Affects multi-tenant VPS / sandbox providers more than end-user desktops.
severity: CVSS 9.3 (Critical)
## cve ids[1]
## affected
- Kernels before stable backports such as 5.10.272, 5.15.223, 6.1.190, 6.6.159, 6.12.113, 6.18.57, 7.2.11 (verify vendor packages)
## fixed in
- Upstream commit 6785011f8b16 and matching stable backports; vendor kernels as listed by distros
## updates by day[4]
▸Oct 14, 2026
permalink ↗Mainline merge / public write-ups.
▸Oct 7, 2026
permalink ↗Upstream IPv4 checksum guard accepted into net.git.
▸Aug 20, 2026
permalink ↗Initial host-memory disclosure reported.
▸Aug 18, 2026
permalink ↗Vercel Sandbox challenge opens.
## news & write-ups[2]
## posts[3]
PwnEscape-Ai Research: Guest-to-Host KVM Escape (CVE-2026-99999). TLDR;- How a $1 million sandbox challenge led us to a vulnerability in Linux networking, repeatable host-memory disclosure, and ultimately a full guest-to-host escape. Blog:- t.co/CJERkG4rsE t.co/gdXbOvkklw
How can one obtain such a great identifier as CVE-2026-99999? #PwnEscape
Just uncovered: the “PwnEscape” Linux kernel flaw (CVE-2026-99999) lets guest VMs read host memory. A 9.3/10 critical issue, exposed via crafted packets in Vercel’s sandbox and patched in recent kernel versions. If you run shared Linux hosts, updating is mandatory. t.co/mqBjjVqe1d
## notes & caveats
No public claim of in-the-wild exploitation. Fixed-version list is indicative — always confirm with your distro’s advisory. CVE id CVE-2026-99999 is the identifier used across pwn.ai / Vercel / community posts.
