CVE-2026-23323 Overview
A vulnerability has been resolved in the Linux kernel affecting the macsmc-hwmon driver for Apple Silicon System Management Controller (SMC) hardware monitoring. The driver contained critical bugs in its sensor population logic and float conversion routines that could lead to out-of-bounds memory access, data corruption, and incorrect values being written to the SMC.
Critical Impact
Local attackers with access to the hwmon interface could trigger out-of-bounds memory access or data corruption, potentially affecting system stability and hardware control on Apple Silicon devices.
Affected Products
- Linux Kernel with macsmc-hwmon driver enabled
- Apple Silicon Mac systems running affected kernel versions
- Systems utilizing hwmon temperature and voltage sensor interfaces
Discovery Timeline
- 2026-03-25 - CVE CVE-2026-23323 published to NVD
- 2026-03-25 - Last updated in NVD database
Technical Details for CVE-2026-23323
Vulnerability Analysis
The macsmc-hwmon driver, responsible for hardware monitoring on Apple Silicon Macs, contained multiple implementation flaws that created potential memory safety issues. The primary vulnerability exists in the voltage sensor population loop, which used an incorrect prefix string ("volt-" instead of "voltage-") when identifying sensors. More critically, the code incorrectly assigned voltage sensors to the temperature sensor array (hwmon->temp.sensors) rather than the proper voltage sensor array (hwmon->volt.sensors).
This array confusion creates a condition where out-of-bounds memory access or data corruption can occur when both temperature and voltage sensors are present on the system. The incorrect array indexing could cause sensors to be written beyond allocated buffer boundaries or overwrite adjacent memory structures.
Additionally, the macsmc_hwmon_write_f32() function contained flawed exponent logic for handling floating-point values greater than or equal to 2^24. The function also lacked proper masking for the mantissa portion of the floating-point representation, which could result in incorrect values being written to the SMC hardware.
Root Cause
The root cause is a coding error in the sensor enumeration logic where voltage sensors were mistakenly assigned to the temperature sensor array. Combined with insufficient input validation in the float conversion routine, this created conditions for memory corruption and incorrect hardware control values.
Attack Vector
An attacker with local access to the hwmon interface could potentially exploit these flaws by:
- Triggering sensor enumeration that causes voltage sensors to corrupt the temperature sensor array
- Manipulating values written through the flawed float conversion routine to write incorrect data to the SMC
- Leveraging the out-of-bounds access to corrupt adjacent kernel memory structures
The vulnerability requires local access and the macsmc-hwmon driver to be loaded, limiting the attack surface to Apple Silicon systems with affected kernel versions.
Detection Methods for CVE-2026-23323
Indicators of Compromise
- Unexpected kernel warnings or errors related to hwmon sensor registration on Apple Silicon systems
- Anomalous behavior in fan control or temperature reporting on affected Macs
- Kernel log entries indicating FIELD_PREP overflow errors in the macsmc module
Detection Strategies
- Monitor kernel logs for warnings or errors mentioning macsmc-hwmon, macsmc_hwmon_write_f32, or sensor registration failures
- Implement kernel module integrity monitoring to detect unauthorized modifications to hwmon drivers
- Review system stability reports for crashes or unexpected behavior related to hardware monitoring subsystems
Monitoring Recommendations
- Enable detailed kernel logging for the hwmon subsystem on Apple Silicon deployments
- Deploy endpoint detection solutions capable of monitoring kernel module behavior and memory access patterns
- Establish baseline behavior for SMC interactions to identify anomalous write operations
How to Mitigate CVE-2026-23323
Immediate Actions Required
- Update to a patched Linux kernel version containing the fix for CVE-2026-23323
- Review deployed Apple Silicon systems running Linux to identify vulnerable kernel versions
- Consider temporarily disabling manual fan control features until patching is complete
- Monitor affected systems for stability issues that may indicate exploitation attempts
Patch Information
The vulnerability has been resolved in the Linux kernel through commits that fix the sensor array assignment logic and correct the float conversion routines. The fix ensures voltage sensors are properly assigned to hwmon->volt.sensors and corrects the exponent and mantissa handling in macsmc_hwmon_write_f32(). Additionally, the function is declared as __always_inline to resolve the FIELD_PREP overflow issue.
Patches are available through the following kernel git commits:
Workarounds
- Disable the macsmc-hwmon module on affected systems if the functionality is not required: modprobe -r macsmc-hwmon
- Restrict access to the hwmon sysfs interface by adjusting file permissions to limit exposure to local users
- Avoid using manual fan control features until the kernel is updated to a patched version
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
