CVE-2021-47101

What it actually does

asix_read_cmd may return fewer bytes than sizeof(smsr), leaving smsr uninitialized and causing use of uninit-value inside asix_check_host_enable called by asix_mdio_read, resulting in kernel memory corruption.

Why it matters to the business

Systems with ASIX USB Ethernet adapters may suffer kernel instability, crashes, or information disclosure that disrupts network connectivity and requires reboots or forensic investigation.

How an attack unfolds

A local attacker loads or triggers the asix driver on a system with a vulnerable USB adapter, issues MDIO read operations that take the short-read path, and causes the kernel to consume uninitialized stack or heap data.

How to fix it

Upgrade the Linux kernel to a version containing the fix for the uninit-value in asix_mdio_read; for affected Ubuntu releases apply the corresponding openssl package updates listed for 14.04 LTS and 16.04 LTS.

How to confirm the fix worked

Confirm the running kernel contains the commit that resolves the short-read path in asix_read_cmd; recompile or boot with KMSAN enabled and verify absence of the uninit-value report in asix_common.c.

Typical attack path

1. Obtain local user access on a Linux host
2. Attach or activate an ASIX-based USB Ethernet device
3. Perform network configuration or traffic that invokes asix_mdio_read
4. Trigger the short-read condition in asix_read_cmd to reach the uninit-value use

How to detect it

Inspect kernel logs for KMSAN reports citing asix_check_host_enable or asix_mdio_read; correlate with USB device insertion events for ASIX VID/PID strings.

• BUG: KMSAN: uninit-value in asix_check_host_enable
• asix_mdio_read+0x3c1/0xb00 drivers/net/usb/asix_common.c

What your security team should do

• Apply kernel updates immediately on systems exposing USB Ethernet ports
• Disable or blacklist the asix driver where the hardware is not required
• Monitor for KMSAN or UBSAN reports mentioning asix_mdio_read