CVE-2022-4744

What it actually does

Double-free in the TUN/TAP driver triggered when register_netdevice fails during NETDEV_REGISTER notifier processing, resulting in memory corruption that can be abused for local denial of service or privilege escalation.

Why it matters to the business

Local attackers on affected Linux systems can crash hosts or obtain root-level access, enabling theft of data, persistence, or lateral movement in servers, containers, and virtualized environments that rely on TUN/TAP interfaces.

How an attack unfolds

An attacker with local access opens or configures a TUN/TAP device in a way that forces register_netdevice to fail; the resulting double-free is then leveraged through heap manipulation to corrupt kernel structures and execute arbitrary code or crash the system.

How to fix it

Upgrade the Linux kernel to a patched release that corrects the double-free in the TUN/TAP driver; apply vendor-supplied updates as soon as they become available and rebuild any custom kernels with the fix incorporated.

How to confirm the fix worked

Confirm the running kernel contains the upstream fix for the TUN/TAP NETDEV_REGISTER double-free; test device registration paths under failure conditions and monitor for crashes or memory errors in the driver.

Typical attack path

1. Gain local shell access on the target Linux host
2. Trigger TUN/TAP device creation or registration that causes register_netdevice to fail
3. Exploit the resulting double-free via heap feng-shui to corrupt kernel memory
4. Escalate privileges to root or cause kernel panic for denial of service

How to detect it

Review kernel logs (dmesg, /var/log/kern.log) for double-free warnings or oops messages involving register_netdevice and tun/tap; correlate with process activity creating or configuring virtual network devices.

What your security team should do

• Prioritize kernel updates on all systems exposing TUN/TAP interfaces
• Limit unprivileged access to /dev/net/tun where operationally feasible
• Enable kernel hardening features such as SLAB_FREELIST_RANDOM and page-table isolation
• Monitor kernel logs for TUN/TAP related oops or warnings