CVE-2026-42806 Overview
CVE-2026-42806 is an out-of-bounds read vulnerability [CWE-125] in the Bosch BME690 SensorAPI (C-driver) versions v1.0.3 and prior. The flaw resides in the read_all_field_data function within bme69x.c. The driver extracts a gas_index value using a 4-bit mask that permits values 0 through 15, but the valid hardware range is only 0 through 9. An attacker with physical access to the I2C or SPI bus, or a compromised peripheral impersonating the sensor, can return a crafted payload that triggers reads up to 6 bytes past a 30-byte stack buffer. The leaked bytes propagate into the public gas_wait field.
Critical Impact
Adjacent stack memory can leak through telemetry or logs, and sensor measurements can be corrupted when a malicious or compromised peripheral supplies an out-of-range gas index on the I2C/SPI bus.
Affected Products
- Bosch BME690 SensorAPI (C-driver) version v1.0.3
- Bosch BME690 SensorAPI (C-driver) versions prior to v1.0.3
- Embedded systems and IoT devices integrating the vulnerable bme69x.c field-data parsing logic
Discovery Timeline
- 2026-09-10 - CVE-2026-42806 published to NVD
- 2026-09-10 - Last updated in NVD database
Technical Details for CVE-2026-42806
Vulnerability Analysis
The BME690 driver prefetches heater configuration registers into a contiguous 30-byte stack buffer named set_val. This buffer maps three tables: IDAC, RES_HEAT, and GAS_WAIT, each holding 10 entries. When parsing sensor field data, the driver reads a gas_index value from the sensor payload using a 4-bit mask. That mask allows values from 0 to 15, but the hardware only defines valid indices 0 through 9.
The driver then performs the indexed access set_val[20 + gas_index] without any bounds check. Supplying a gas_index of 10 or higher shifts the read past the end of the stack buffer, returning up to 6 bytes of adjacent stack memory. The out-of-bounds byte is stored into the public gas_wait structure field and surfaces wherever the host application logs or telemeters sensor state.
Root Cause
The root cause is missing input validation on attacker-influenced data before it drives an array index. The 4-bit extraction produces a wider range than the underlying set_val layout supports, and the code omits a comparison against the maximum valid gas index of 9 before dereferencing the buffer.
Attack Vector
Exploitation requires physical access to the I2C or SPI bus that connects the host microcontroller to the BME690, or a compromised peripheral capable of impersonating the sensor. The attacker returns a crafted field-data payload with a gas_index of 10 to 15. The driver then reads memory past set_val, and any downstream telemetry stream that publishes gas_wait can leak that memory to an observer. See the Bosch Security Advisory BOSCH-SA-223618 for vendor details.
Detection Methods for CVE-2026-42806
Indicators of Compromise
- Sensor telemetry containing gas_wait values outside documented ranges or that fluctuate without a corresponding configuration change.
- Unexpected I2C/SPI bus activity, address collisions, or peripherals presenting the BME690 device signature from unauthorized locations.
- Measurement corruption or gas_index values greater than 9 observed in device logs or upstream analytics pipelines.
Detection Strategies
- Instrument the host firmware to validate gas_index after extraction and log any value greater than 9 as a security event.
- Perform static analysis of firmware images that link bme69x.c to confirm the driver version and detect unpatched read_all_field_data implementations.
- Correlate anomalies in gas-sensor telemetry with bus-level events collected from logic analyzers or bus-monitoring hardware in high-assurance deployments.
Monitoring Recommendations
- Baseline expected ranges for gas_wait and other BME690 fields, then alert on deviations at the ingestion layer of the IoT data pipeline.
- Monitor firmware inventory for devices still shipping BME690 SensorAPI v1.0.3 or earlier and flag them for update.
- Track physical-tamper indicators such as enclosure switches, secure boot attestations, and unexpected device resets on affected hardware.
How to Mitigate CVE-2026-42806
Immediate Actions Required
- Inventory all firmware and products that embed the Bosch BME690 SensorAPI C-driver and identify versions at or below v1.0.3.
- Apply the vendor-supplied update once available and rebuild affected firmware images.
- Restrict physical access to devices that expose the I2C/SPI bus to untrusted environments.
Patch Information
Refer to the Bosch Security Advisory BOSCH-SA-223618 for the fixed driver version and integration guidance. Vendors that vendor-in bme69x.c should update their forks and re-release downstream firmware.
Workarounds
- Patch the driver locally by adding a bounds check that rejects any gas_index greater than 9 before the set_val[20 + gas_index] access.
- Sanitize telemetry pipelines so that gas_wait values are clamped or discarded when the associated gas_index is outside the valid range.
- Enforce hardware measures such as tamper-evident enclosures, sealed connectors, and secure boot to reduce the physical attack surface.
Disclaimer: This content was generated using AI. While we strive for accuracy, please verify critical information with official sources.
