CVE-2021-46991

What it actually does

Use-after-free in the i40e network driver where i40e_client_del_instance frees pf->cinst but code continues to dereference pf->cinst->lan_info, allowing memory corruption or kernel crash.

Why it matters to the business

Potential system instability, denial of service, or local privilege escalation on systems using Intel i40e Ethernet adapters, increasing operational risk and requiring urgent patching to maintain uptime and security posture.

How an attack unfolds

An attacker with local access triggers the i40e_client_subtask path under specific client instance conditions, causing the free-then-use sequence that can be leveraged to corrupt kernel memory structures for code execution or crash.

How to fix it

Update the Linux kernel to a version containing the commit that adds the missing return after i40e_client_del_instance in i40e_client_subtask; rebuild and deploy the updated kernel image across affected systems.

How to confirm the fix worked

Confirm the fix is present by inspecting the i40e driver source for the added return statement after the client instance deletion call, then verify the running kernel version matches or exceeds the patched release.

Typical attack path

1. Obtain local access on a Linux system with i40e hardware and driver loaded
2. Trigger or wait for i40e_client_subtask execution under conditions that invoke i40e_client_del_instance
3. Exploit the subsequent access to the freed pf->cinst pointer to corrupt memory or escalate privileges
4. Achieve kernel-level impact such as DoS or arbitrary code execution

How to detect it

Examine kernel logs for oops or panic messages referencing i40e_client_subtask or use-after-free in the i40e module; correlate with process activity that interacts with network client instances.

What your security team should do

• Prioritize kernel updates on all systems using i40e adapters within standard change windows
• Monitor for new kernel releases and test the patched driver in staging environments
• Review local access controls and driver usage to reduce exposure surface until patched