CVE-2026-98678: Linux Kernel IIO ADC Input Validation Flaw

CVE-2026-98678 Overview

CVE-2026-98678 affects the Linux kernel's Industrial I/O (IIO) subsystem, specifically the ad4030 analog-to-digital converter (ADC) driver. The flaw resides in the ad4030_set_avg_frame_len() function, where the driver computes a logarithm using ilog2() before validating the input value. Passing zero or a negative value produces an undefined result from ilog2(), leading to unpredictable driver behavior.

The maintainers resolved the issue by validating that the input is strictly positive before computing its logarithm.

Critical Impact
Local users with access to the IIO sysfs interface for the AD4030 ADC can trigger undefined behavior in the kernel driver by supplying zero or negative oversampling ratio values.

Affected Products

Linux kernel versions containing the ad4030 IIO ADC driver prior to the fix
Systems using Analog Devices AD4030 ADC hardware with the mainline IIO driver
Stable kernel branches referenced by commits 6b0cc4e3, 6ca6dcba, and d6152105

Discovery Timeline

2026-10-18 - CVE-2026-98678 published to NVD
2026-10-19 - Last updated in NVD database

Technical Details for CVE-2026-98678

Vulnerability Analysis

The ad4030 driver supports configurable oversampling, where the average frame length is derived from the oversampling ratio. The function ad4030_set_avg_frame_len() calls ilog2() on the provided ratio to determine the frame length encoding written to the ADC configuration register.

The original implementation performed this logarithm calculation before verifying that the input was a valid positive integer. The ilog2() macro is defined only for positive values; invoking it with zero or a negative integer yields undefined results and may propagate incorrect values into driver state.

The fix reorders the logic so that input validation occurs first. Non-positive values are rejected before any logarithmic computation takes place, preventing undefined kernel behavior stemming from malformed userspace input.

Root Cause

The root cause is improper input validation (an input validation error) in the ordering of operations within ad4030_set_avg_frame_len(). The driver trusted the oversampling ratio supplied through the IIO interface and computed ilog2() prior to any range check, violating the preconditions of the underlying bit-scan operation.

Attack Vector

Exploitation requires local access to the affected system and write permissions on the IIO sysfs attributes exposed by the ad4030 driver. An attacker or a misbehaving userspace component can write a non-positive oversampling ratio to the relevant attribute, causing the driver to execute ilog2() with an invalid argument. The consequence is undefined driver state rather than a confirmed memory corruption primitive, so impact is limited to driver reliability and device integrity on systems that expose AD4030 hardware.

No public proof-of-concept exploit is associated with this CVE, and the issue is not listed in the CISA Known Exploited Vulnerabilities catalog.

Detection Methods for CVE-2026-98678

Indicators of Compromise

Unexpected kernel log messages originating from the ad4030 driver or IIO subsystem after writes to oversampling-related sysfs attributes.
Anomalous ADC readings or device state transitions on hardware using the AD4030 part.
Processes writing non-positive values to /sys/bus/iio/devices/iio:deviceN/ attributes tied to oversampling.

Detection Strategies

Audit kernel versions on Linux hosts and embedded systems to identify builds that include the vulnerable ad4030 driver without the referenced stable commits.
Monitor sysfs write events on IIO device nodes using auditd rules targeting the IIO device paths.
Review package inventories to confirm whether vendor kernels have backported the fixes identified by commits 6b0cc4e3, 6ca6dcba, and d6152105.

Monitoring Recommendations

Centralize kernel logs (dmesg, journald) and alert on IIO subsystem warnings referencing ad4030.
Track changes to kernel modules on production hosts and correlate with patch deployment windows.
Baseline userspace processes that interact with IIO sysfs to detect unauthorized writes.

How to Mitigate CVE-2026-98678

Immediate Actions Required

Apply the upstream Linux kernel fixes referenced by commits 6b0cc4e3, 6ca6dcba, and d6152105.
Rebuild or update affected kernel packages on systems that integrate Analog Devices AD4030 ADC hardware.
Restrict write access to IIO sysfs attributes to privileged users only.

Patch Information

The fix validates that the oversampling ratio argument is strictly positive before invoking ilog2() inside ad4030_set_avg_frame_len(). Distribution maintainers should pick up the referenced stable commits and ship updated kernel packages. Users of custom or embedded kernels building against mainline sources should rebase on a kernel that includes the fix.

Workarounds

Unload or blacklist the ad4030 driver on systems that do not require AD4030 ADC functionality until a patched kernel is deployed.
Enforce strict file permissions on /sys/bus/iio/devices/ entries so only trusted service accounts can modify ADC configuration.
Validate oversampling ratio values in any userspace service that writes to the affected sysfs attributes.

bash

# Example: restrict IIO sysfs write access and blacklist the vulnerable driver
# Blacklist the module if AD4030 hardware is not in use
echo 'blacklist ad4030' | sudo tee /etc/modprobe.d/ad4030-blacklist.conf
sudo modprobe -r ad4030 2>/dev/null || true

# Tighten permissions on IIO sysfs attributes
sudo find /sys/bus/iio/devices -name 'oversampling*' -exec chmod 600 {} \;