CVE-2026-18414

Overview

CVE-2026-18414 is a buffer overrun in Zephyr's ADI MAX32 ADC driver that lets unprivileged user-mode threads write beyond the supplied buffer, potentially corrupting kernel memory. The flaw stems from an incorrect buffer size check that ignores sample width, and the kernel system call does not enforce bounds. This can lead to privilege escalation or denial of service.

Description

The ADC API requires each driver to reject a sampling sequence whose destination buffer is too small: the buffer_size field of struct adc_sequence in include/zephyr/drivers/adc.h documents that "the driver must ensure that samples are not written beyond the limit and it must return an error if the buffer turns out to be not large enough". The ADI MAX32 driver did not honour that contract. start_read() in drivers/adc/adc_max32.c compared buffer_size, a byte count, against a sample count ((1 + extra_samplings) channels), ignoring sizeof(uint16_t), so it accepted a buffer half the required size. The samples are then stored through the uint16_t data->buffer by Wrap_MXC_ADC_GetData(), which writes two bytes per sample and advances the pointer by one uint16_t: in adc_max32_start_channel() for synchronous reads, and in adc_max32_isr() for asynchronous ones. A sequence selecting two channels with a two-byte buffer, for example, passes the check and has its second sample written past the end of the buffer. On a build with CONFIG_USERSPACE, adc_read() and adc_read_async() are system calls. The handler in drivers/adc/adc_handlers.c copies the sequence in from user memory, verifies only that [buffer, buffer + buffer_size) is writable by the calling thread, and rejects a user-supplied options->callback; it deliberately leaves the size arithmetic to the driver. A user-mode thread that has been granted access to a MAX32 ADC device object therefore fully controls channels, buffer, buffer_size and options->extra_samplings, and can make the driver write twice as many bytes as its buffer holds. Because the check scales with extra_samplings, the overrun equals the length of the buffer itself, up to channels * 65536 bytes past its end, since the sample pointer is only rewound on a repeat sampling, never on the extra samplings of a sequence. The resulting stores are performed by the driver in kernel mode (in the system call itself, the ADC context timer, or the ADC interrupt handler for asynchronous reads), where the MPU does not restrict the thread's memory domain, so the write walks linearly out of the user partition and into adjacent memory such as other partitions, kernel data or thread stacks. The impact is kernel-memory corruption of attacker-chosen length at an attacker-chosen offset, a plausible privilege-escalation and denial-of-service primitive from an unprivileged user-mode thread. Builds without CONFIG_USERSPACE are affected only as a caller-side robustness defect, since the application itself supplies the buffer. The fix replaces that check in start_read() with a call to the new shared helper adc_sequence_validate_buffer() in drivers/adc/adc_common.c, passing sizeof(uint16_t) as the sample size. The helper computes active_channels sizeof(uint16_t) (1 + extra_samplings) and returns -ENOMEM before any sampling is started.

Impact

Confidentiality: kernel memory contents may be exposed. Integrity: kernel memory corruption can enable arbitrary code execution. Availability: the system may crash, causing denial of service. The vulnerability is exploitable from any unprivileged user-mode thread that has access to the ADC device object, making it a local privilege escalation vector.

Remediation

Apply the official Zephyr patch that replaces the buffer size check with adc_sequence_validate_buffer() and passes sizeof(uint16_t). If patching is delayed, disable CONFIG_ADC_MAX32 or restrict ADC device access to privileged threads, or turn off CONFIG_USERSPACE. Additionally, enable stricter MPU bounds or stack canaries to detect overruns.

Risk context

High severity (CVSS 7.8) with no EPSS data; defenders should treat it as a high-priority vulnerability that can lead to kernel compromise.

Affected products

• Zephyr RTOS
• ADI MAX32 ADC driver
• Zephyr ADC subsystem
• Zephyr CONFIG_USERSPACE
• Zephyr ADC_MAX32 driver