CVE-2026-63966: Linux Kernel Information Disclosure Bug

CVE-2026-63966 Overview

CVE-2026-63966 is an uninitialized memory disclosure vulnerability in the Linux kernel Industrial I/O (IIO) Inertial Measurement Unit (IMU) driver for the Analog Devices ADIS16550. The adis16550_trigger_handler() function declares its scan data buffer on the stack without zero-initialization. Each trigger event leaks four bytes of kernel stack memory to userspace through the IIO buffer interface. The patch resolves the flaw by zero-initializing the on-stack structure before use.

Critical Impact
Local users with access to the IIO buffer character device can read uninitialized kernel stack bytes on every trigger, enabling incremental leakage of sensitive kernel data such as pointers or stack canaries useful for defeating KASLR and preparing further exploitation.

Affected Products

Linux kernel builds that include the iio-imu-adis16550 driver
Systems using Analog Devices ADIS16550 IMU sensors over SPI
Downstream distributions shipping the affected IIO IMU subsystem until stable backports are applied

Discovery Timeline

2026-07-19 - CVE-2026-63966 published to the National Vulnerability Database
2026-07-19 - Last updated in NVD database

Technical Details for CVE-2026-63966

Vulnerability Analysis

The defect resides in the trigger handler of the ADIS16550 IIO driver. The function allocates a scan data structure on the stack to hold sensor samples that are copied to a per-device buffer before being pushed to userspace via iio_push_to_buffers_with_timestamp().

The memcpy() call populates only the first 28 bytes of that structure, corresponding to one temperature channel plus six channels of gyroscope and accelerometer data. The trailing s64 timestamp is written at the 8-byte-aligned offset 32. Bytes 28 through 31 act as alignment padding and are never written, so they retain whatever kernel stack contents occupied that memory previously. This is a classic uninitialized memory use pattern [CWE-908] leading to information exposure [CWE-200].

Root Cause

The root cause is missing initialization of a compound stack buffer that includes implicit padding for timestamp alignment. C does not zero stack variables by default, and the driver assumed that filling the sensor channel fields would cover the entire structure. Because IIO enforces 8-byte alignment of the appended timestamp, four bytes of padding sit between the channel data and the timestamp, and those bytes are copied verbatim to the ring buffer exposed to userspace.

Attack Vector

A local attacker who can open the IIO character device for the ADIS16550 (typically /dev/iio:deviceN) and enable buffered capture triggers the handler repeatedly. Each trigger event delivers a sample record containing four bytes of stack residue. Repeated sampling aggregates enough leaked data to reconstruct kernel pointers, function addresses, or other sensitive values that assist in bypassing KASLR or crafting follow-on kernel exploits. No privileged operation is required beyond access to the IIO device node, which is often granted to sensor-consuming user services.

No public proof-of-concept code is referenced in the advisory. The fix applied in the upstream commits zero-initializes the on-stack structure, eliminating the padding leak.

Detection Methods for CVE-2026-63966

Indicators of Compromise

Unexpected processes opening /dev/iio:device* nodes associated with the ADIS16550 driver on systems where sensor consumption is not part of normal workflows
High-frequency reads from IIO buffer file descriptors by non-sensor userland processes
Kernel modules matching adis16550 loaded on hosts that do not require IMU functionality

Detection Strategies

Audit /sys/bus/iio/devices/ enumeration and correlate device access with the processes performing read() and ioctl() on IIO buffer nodes
Compare running kernel uname -r output against distribution advisories that reference the stable commits 474f8928d50b, c2c25544439, and ce582b22dd2f
Flag any container or unprivileged process that gains read access to IIO device nodes exposing IMU sensors

Monitoring Recommendations

Enable Linux Audit rules on /dev/iio:device* open, read, and ioctl syscalls
Track kernel package versions across the fleet and alert when hosts run unpatched builds of the affected driver
Monitor for sustained buffered IIO reads that do not correlate with expected telemetry collectors

How to Mitigate CVE-2026-63966

Immediate Actions Required

Apply the stable kernel updates containing commits 474f8928d50b09f7dcf507049f08732640b88b49, c2c255444392872cbbf46d640cb3a938e8000309, and ce582b22dd2ff15ac99101c22ec1559d1febe2ff
Restrict access to /dev/iio:device* nodes to trusted sensor daemons through file permissions or udev rules
Rebuild custom kernels that vendor the iio-imu-adis16550 driver against the fixed source tree

Patch Information

The upstream fix zero-initializes the scan data structure on the stack so that padding bytes between sensor channels and the appended timestamp cannot leak to userspace. Distribution-specific patched packages should be tracked through vendor advisories. Reference the Linux Kernel Commit Log entries: 474f8928d50b, c2c25544439, and ce582b22dd2f.

Workarounds

Unload the adis16550 module with modprobe -r adis16550 on systems that do not require the sensor
Blacklist the driver in /etc/modprobe.d/ where ADIS16550 hardware is not present or not used
Tighten udev permissions on IIO device nodes so that only vetted service accounts can open the buffer interface

bash

# Blacklist the adis16550 driver where the IMU is not required
echo 'blacklist adis16550' | sudo tee /etc/modprobe.d/blacklist-adis16550.conf
sudo depmod -a
sudo modprobe -r adis16550 2>/dev/null || true

# Restrict IIO device access to a dedicated group
sudo groupadd -f iio-users
cat <<'EOF' | sudo tee /etc/udev/rules.d/90-iio-restrict.rules
SUBSYSTEM=="iio", KERNEL=="iio:device*", GROUP="iio-users", MODE="0640"
EOF
sudo udevadm control --reload-rules && sudo udevadm trigger