CVE-2024-56769

What it actually does

Uninitialized local u8 buffer passed to i2c_transfer in dib3000_read_reg can retain undefined values on failure, which are then used without sanitization in dib3000mb_attach leading to KMSAN-reported uninit-value use.

Why it matters to the business

Systems relying on specific DVB-USB tuner hardware may experience crashes or unpredictable behavior during device initialization, increasing support costs and downtime for media-related workloads; low exploitability keeps overall risk limited despite wide kernel deployment.

How an attack unfolds

An attacker with local access crafts conditions to trigger dibusb_probe and subsequent frontend attach where i2c_transfer fails, allowing the uninitialized buffer contents to propagate and potentially cause denial-of-service or limited information exposure in the kernel driver path.

How to fix it

Update to a kernel containing the fix that zeros the rb buffer before i2c_transfer; for the listed chromium-browser packages on Ubuntu 14.04 LTS apply version 53.0.2785.143-0ubuntu0.14.04.1.1142 or later. Reboot after upgrade and verify driver initialization succeeds without KMSAN warnings.

How to confirm the fix worked

Confirm the patch is present by checking the dib3000mb.c source for the zeroing of rb prior to i2c_transfer; run syzkaller or KMSAN on the dibusb probe path and ensure no uninit-value reports occur; test device attachment under simulated i2c failure conditions.

Typical attack path

1. Load or hot-plug a vulnerable dvb-usb device handled by dibusb-mb
2. Force i2c_transfer failure during dib3000_read_reg inside dib3000mb_attach
3. Observe or abuse the resulting uninitialized buffer values in kernel context

How to detect it

Search kernel logs for 'BUG: KMSAN: uninit-value' combined with dib3000mb_attach or dib3000_read_reg stack traces; inspect dmesg and journalctl for 'dvb-usb: bulk message failed' messages around device probe events; review i2c transfer error paths for signs of repeated failures.

What your security team should do

• Prioritize kernel updates on any hosts exposing DVB-USB hardware even though KEV status is false
• Monitor EPSS trend stability and reassess if new threat actor activity appears
• Restrict unprivileged local access to media device nodes as a temporary control
• Include the dib3000_read_reg path in future kernel fuzzing campaigns