NULL Pointer Dereference in Zephyr RTOS MCUmgr Serial Transport

Publication date: 2026-06-29

Last updated on: 2026-06-29

Assigner: Zephyr Project

Description

mcumgr_serial_process_frag() in subsys/mgmt/mcumgr/transport/src/serial_util.c calls net_buf_reset() on the result of smp_packet_alloc() before checking it for NULL. smp_packet_alloc() uses net_buf_alloc(K_NO_WAIT) against the shared MCUmgr packet pool (CONFIG_MCUMGR_TRANSPORT_NETBUF_COUNT, default 4), which returns NULL when the pool is exhausted. In default builds the __ASSERT_NO_MSG in net_buf_reset is a no-op, so net_buf_simple_reset writes through the NULL pointer (buf->len = 0; buf->data = buf->__buf), causing a fault/crash. The fragment data reaches this code from attacker-controlled bytes on the MCUmgr serial/UART/shell-console transports (smp_uart.c, smp_raw_uart.c, smp_shell.c), and a fresh buffer is allocated at the start of essentially every new packet. An attacker on the serial/console link can flood the transport to drive the 4-entry buffer pool to exhaustion and induce the NULL dereference, crashing the device (denial of service). The defect was introduced after the original MCUmgr rework and shipped in Zephyr v4.4.0. The fix moves the NULL check ahead of net_buf_reset.

CVSS Scores

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Meta Information

Published

2026-06-29

Last Modified

2026-06-29

Generated

2026-06-30

AI Q&A

2026-06-30

EPSS Evaluated

N/A

NVD

CVE-2026-10648

Affected Vendors & Products

Vendor	Product	Version / Range
zephyr_project	zephyr	4.4.0

Helpful Resources

Exploitability

CWE

KEV

CWE ID	Description
CWE-476	The product dereferences a pointer that it expects to be valid but is NULL.

Attack-Flow Graph

Executive Summary

This vulnerability occurs in the mcumgr_serial_process_frag() function of the Zephyr project. The function calls net_buf_reset() on a buffer allocated by smp_packet_alloc() without first checking if the allocation returned NULL. When the shared MCUmgr packet pool is exhausted, smp_packet_alloc() returns NULL, causing net_buf_reset() to write through a NULL pointer, which leads to a fault or crash.

An attacker can exploit this by flooding the MCUmgr serial/UART/shell-console transport with packets, exhausting the limited buffer pool and triggering the NULL pointer dereference, resulting in a denial of service (device crash).

Impact Analysis

This vulnerability can cause a denial of service by crashing the affected device. An attacker with access to the serial or console interface can flood the device with packets, exhausting the buffer pool and triggering a NULL pointer dereference that crashes the device.

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