Summary
CVE-2026-51082: Proxmox VNC session hijack via race between vncproxy and vncwebsocket (PVE <9.1.9/<8.4.19).
Affected Asset
Proxmox VE 9.x / 8.x (pve-manager before 9.1.9/8.4.19; qemu-server before 9.1.7/8.4.7; pve-container before 6.1.3/5.3.4 — VNC session hijack via race between vncproxy/vncwebsocket).
Affected Endpoint
vncproxy API endpoint / vncwebsocket API endpoint
Prerequisites
Proxmox VE 9.x or 8.x below the fixed versions; authenticated user with privileges to call vncproxy while another user opens a VNC session in parallel.
Steps to Reproduce
As an authenticated user with privilege to call vncproxy, open a VNC session in parallel while another user opens one too; race the getaddrinfo() lookup to hijack the concurrent session window.
Evidence
Public advisory (Noxen) and NVD entry; confirmed container escape demonstrations on Proxmox / LXC homelab setups.
Impact
Critical container escape on homelab hosts; attacker can write /root/.ssh/authorized_keys or read /etc/shadow from inside an unprivileged container; full host compromise.
Root Cause
runc did not properly restrict access to host-side file descriptors within the container's /proc view, allowing a malicious container to reference and chdir into leaked descriptors.
Remediation
Update runc to 1.1.12+; on Proxmox: apt update && apt dist-upgrade (pve-container / lxc-pve packages from Feb 2024); verify with runc --version.
Verification Steps
Confirm pve-manager, qemu-server, pve-container versions meet fixed releases (9.1.9/8.4.19, 9.1.7/8.4.7, 6.1.3/5.3.4); verify concurrent VNC session requests are serialized.