CVE-2026-18413 in Zephyr
Summary
by MITRE • 09/28/2026
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 NXP MCUX LPADC driver did not honour that contract. mcux_lpadc_start_read() in drivers/adc/adc_mcux_lpadc.c performed no buffer-size check at all before assigning data->buffer = sequence->buffer. Each completed conversion then stores one 16-bit sample per enabled channel per sampling round through an unbounded *data->buffer++: in mcux_lpadc_isr() for interrupt-driven builds, and in mcux_lpadc_dma_callback() for DMA-driven builds on releases that have the DMA path. A sequence selecting two channels with a two-byte buffer, for example, 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 an LPADC device object therefore fully controls channels, buffer, buffer_size and options->extra_samplings, and can request far more samples than its buffer can hold: up to channels * 65536 samples into a two-byte buffer, 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 ADC interrupt handler or the DMA completion callback), 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 calls the new shared helper adc_sequence_validate_buffer() in drivers/adc/adc_common.c from mcux_lpadc_start_read(). The helper computes active_channels sizeof(uint16_t) (1 + extra_samplings) and returns -ENOMEM before any sampling is started.
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Analysis
by VulDB Data Team • 09/28/2026
The NXP MCUX Low Power Analog-to-Digital Converter driver contains a critical buffer overflow vulnerability stemming from the absence of input validation for sample sequence parameters. The Zephyr ADC API contract explicitly mandates that drivers must verify whether the provided destination buffer is sufficiently large to hold all expected samples and return an error if it is not. However, the mcux_lpadc_start_read function failed to implement this check before proceeding with data acquisition operations. This oversight allows a caller to specify a sampling sequence where the calculated number of required samples exceeds the allocated memory size of the destination buffer. When such a mismatch occurs, the driver proceeds to write conversion results into the undersized buffer without bounds checking, leading directly to heap-based or stack-based buffer overflow conditions depending on how the buffer was allocated by the calling application.
The vulnerability is particularly severe in systems configured with user-space isolation enabled via CONFIG_USERSPACE because it allows unprivileged applications to trigger kernel-mode memory corruption. In this configuration, adc_read and adc_read_async operate as system calls that copy sequence structures from user space into kernel space. While the system call handler performs basic validation to ensure the buffer region is writable by the calling thread, it deliberately delegates size arithmetic verification to individual drivers. Consequently, an unprivileged user-mode thread with access to an LPADC device object can fully control parameters such as channel selection, buffer address, buffer size, and extra sampling counts. By requesting a large number of samples relative to a small buffer allocation, typically up to channels multiplied by sixty-five thousand five hundred thirty-six samples into a minimal two-byte buffer, the attacker forces the driver to perform unbounded memory writes during interrupt handling or DMA completion callbacks.
The operational impact involves kernel-memory corruption at an attacker-controlled offset and length. Because these write operations occur within the context of the ADC interrupt handler or DMA callback, they execute in kernel mode where Memory Protection Unit restrictions do not apply to the thread's current domain. The unbounded pointer incrementing mechanism causes writes to walk linearly out of the user partition into adjacent memory regions. This can corrupt other partitions, overwrite critical kernel data structures, or destroy thread stacks on the heap. Such corruption serves as a potent primitive for privilege escalation from an unprivileged context to full system control and also presents a significant denial-of-service risk by destabilizing core operating system functions through memory overwrites.
This vulnerability maps directly to CWE-120 Buffer Copy without Checking Size of Input, which describes classic buffer overflow scenarios where input data exceeds the allocated buffer capacity. Furthermore, from an offensive security perspective aligned with MITRE ATT&CK techniques, this flaw facilitates privilege escalation by allowing a lower-integrity process to manipulate high-integrity kernel memory. The exploitation path leverages improper validation of user-supplied inputs within privileged execution contexts, enabling attackers to bypass isolation boundaries and execute arbitrary code or crash the system through controlled memory corruption events triggered via standard hardware abstraction layer interfaces.
The remediation strategy involves integrating a shared validation helper function named adc_sequence_validate_buffer into the driver initialization flow. This utility computes the total required buffer size by multiplying the number of active channels, the size of each sample in bytes, and one plus any extra sampling requests configured for the sequence. If the computed requirement exceeds the provided buffer_size field, the function returns an error code such as -ENOMEM before any sampling activity begins. By enforcing this check at mcux_lpadc_start_read, the driver ensures that undersized buffers are rejected early in the process flow, preventing subsequent unbounded writes during interrupt or DMA callbacks and effectively neutralizing both privilege escalation and denial-of-service vectors associated with this flaw.