CVE-2026-63931 Overview
CVE-2026-63931 is a division-by-zero vulnerability in the Linux kernel's Industrial I/O (IIO) subsystem, specifically in the scd30 chemical sensor driver. The flaw resides in the write_raw handler used when setting the sampling frequency through the sampling_frequency sysfs attribute. A local user writing a zero fractional part (val2) to that attribute triggers a division by zero in kernel context. The Linux kernel maintainers have resolved the issue by adding a zero check for val2 before it is used as a divisor.
Critical Impact
A local user with write access to the sampling_frequency sysfs attribute of the scd30 IIO device can trigger a kernel-level division by zero, resulting in a denial-of-service condition.
Affected Products
- Linux kernel builds including the iio: chemical: scd30 driver prior to the fix
- Distributions shipping stable kernels that include the scd30 driver without the referenced patches
- Systems exposing the scd30 sensor sampling_frequency sysfs attribute to non-root users
Discovery Timeline
- 2026-07-19 - CVE-2026-63931 published to the National Vulnerability Database
- 2026-07-19 - Last updated in NVD database
Technical Details for CVE-2026-63931
Vulnerability Analysis
The vulnerability affects drivers/iio/chemical/scd30_core.c, which implements the IIO driver for the Sensirion SCD30 CO2 sensor. When a user writes to the sampling_frequency sysfs attribute, the IIO core parses the value into two integer parts: val (integer) and val2 (fractional micro component). The driver then uses val2 as a divisor when computing the sampling interval.
Writing a value with a zero fractional part causes val2 to be zero. The driver did not validate this input before performing the division, so the operation executed in kernel context and triggered a divide-by-zero exception. On most architectures this results in an oops or panic, terminating the calling process and potentially destabilizing the kernel.
The fix adds an explicit zero check on val2 prior to using it as a divisor and returns an error to userspace when the value is invalid.
Root Cause
The root cause is missing input validation in the write_raw callback of the scd30 driver. User-supplied fractional input from sysfs is used directly in an arithmetic division without confirming it is non-zero, allowing a division by zero in kernel space.
Attack Vector
Exploitation requires local access with permission to write to the scd30 IIO device's sampling_frequency sysfs node. An attacker with such access issues a write containing a zero fractional part, for example a value like 0.0, which the driver parses into val=0, val2=0. The kernel then attempts the division and faults. There is no known path for remote exploitation or privilege escalation; the primary impact is denial of service.
No verified public proof-of-concept code is available. Refer to the upstream kernel commits linked in the references for the exact patch content and affected code paths.
Detection Methods for CVE-2026-63931
Indicators of Compromise
- Kernel Oops or divide error messages in dmesg referencing scd30 or IIO write paths
- Unexpected process termination when writing to /sys/bus/iio/devices/iio:deviceX/sampling_frequency on systems with the scd30 sensor
- Repeated writes of malformed or zero-fractional values to IIO sampling_frequency attributes originating from unprivileged users
Detection Strategies
- Monitor kernel logs (journalctl -k, /var/log/kern.log) for divide_error or Oops entries associated with the scd30 module or iio_write_raw call chains
- Audit writes to IIO sysfs attributes using Linux Auditing System rules on /sys/bus/iio/devices/*/sampling_frequency
- Compare running kernel versions against the fixed commits listed in the NVD reference set to identify unpatched hosts
Monitoring Recommendations
- Enable kernel crash and oops collection (kdump, systemd-coredump) to capture faults for post-incident analysis
- Alert on repeated kernel faults from the same non-root UID within a short window
- Track IIO driver load events (scd30_i2c, scd30_serial) to inventory affected hosts
How to Mitigate CVE-2026-63931
Immediate Actions Required
- Update the Linux kernel to a stable release containing one of the fixing commits referenced in the NVD advisory
- Restrict write permissions on /sys/bus/iio/devices/*/sampling_frequency to privileged users on systems where the scd30 driver is loaded
- If the sensor is not required, unload or blacklist the scd30_core, scd30_i2c, and scd30_serial modules
Patch Information
The fix adds a zero check for val2 in the scd30 write_raw handler before using it as a divisor. Patches are available in the following upstream stable kernel commits: Linux Kernel Commit 2c50c017, Linux Kernel Commit 4748bce4, Linux Kernel Commit 5aba4f94, Linux Kernel Commit 5e4d3409, Linux Kernel Commit 6308b812, Linux Kernel Commit c7a740bf, Linux Kernel Commit d98c2e69, and Linux Kernel Commit e85bc501. Apply the stable kernel release that corresponds to your distribution branch.
Workarounds
- Tighten Unix permissions on the affected sysfs node so that only root can write to sampling_frequency
- Blacklist the scd30 driver modules on systems that do not require the sensor
- Use a udev rule to restrict access to IIO chemical sensor devices to a trusted group
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
